SharpMuPDF/mupdf/source/html/html-layout.c

// Copyright (C) 2004-2025 Artifex Software, Inc.
//
// This file is part of MuPDF.
//
// MuPDF is free software: you can redistribute it and/or modify it under the
// terms of the GNU Affero General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
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// FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
// details.
//
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// along with MuPDF. If not, see <https://www.gnu.org/licenses/agpl-3.0.en.html>
//
// Alternative licensing terms are available from the licensor.
// For commercial licensing, see <https://www.artifex.com/> or contact
// Artifex Software, Inc., 39 Mesa Street, Suite 108A, San Francisco,
// CA 94129, USA, for further information.

#include "mupdf/fitz.h"
#include "mupdf/ucdn.h"
#include "html-imp.h"

#include "hb.h"
#include "hb-ft.h"
#include <ft2build.h>

#include <math.h>
#include <assert.h>

#undef DEBUG_HARFBUZZ

/*
	Some notes on the layout code below and the concepts used.

	THE MODEL:

	The standard CSS box model is used here. Each box has a margin, a border, padding, and content, any of which can be zero in size.

	+-------------------------------------------------------------------+
	| margin                                                            |
	|        +-------------------------------------------------+        |
	|        | border                                          |        |
	|        |        +-------------------------------+        |        |
	|        |        | padding                       |        |        |
	|        |        |           +---------+         |        |        |
	|        |        |           | content |         |        |        |
	|        |        |           +---------+         |        |        |
	|        |        |                               |        |        |
	|        |        +-------------------------------+        |        |
	|        |                                                 |        |
	|        +-------------------------------------------------+        |
	|                                                                   |
	+-------------------------------------------------------------------+

	In our structures, the box->x,y,w,b refer to the bounding box of the content section alone. The margins/borders/paddings are applied
	to the outside of this automatically.

	HOW WE LAYOUT:

	Our implementation is a 'simple' recursive descent of the structure. We know the width of the area we are laying out into at each point,
	and we know the top/left coords of the enclosing block. So we start with a well defined left/top point, offset that for margins/borders/padding
	etc, calculate the width from the enclosing width (via the CSS). We set the height of the content to be zero to start with, and after laying
	out each of (any) child elements, we ensure that the base of our box is always large enough to enclose the child's boxes with the appropriate
	padding.

	VERTICAL MARGIN COLLAPSE:

	The big complexity in this code is the need to do 'vertical margin collapse'. Basically, if we have 2 blocks, laid out vertically from one
	another, the margin between them is collapsed to be the larger of margins of the two blocks, rather than the sum of the margins of the
	two blocks.

	So block A with a margin of 30, and block B with a margin of 20 will be separated by 30, not 50.

	To make matters more complicated, margin collapse can happen 'through' nestings of blocks, and even through empty blocks. It cannot
	happen through blocks with borders, or padding.

	Accordingly, as we recursively pass through our structure laying out, we keep a 'vertical' parameter, representing the amount of vertical
	space to be considered for collapse. This is set to zero if we hit borders or padding or non-zero height content boxes, and our margins are
	adjusted by it.

	While the margins of a block may be adjusted by a parent 'inheriting' those margins, the bbox of the content of a block will never be
	changed.

	NON-RESTARTING OPERATION:

	The standard layout operation as used for HTML documents and ebooks has us layout onto an infinitely long page, with the vertical
	offsets of boxes adjusted so that a given line of text (or image) never spans a page end (defined to be a multiple of page_h). This
	layout can proceed from start to finish with no need to stop. This is achieved by calling the code with restart == NULL.

	RESTARTING:

	In order to cope with laying out a text story into multiple (potentially differently sized) areas, we need to be able to stop the layout
	when the available area is full, and restart again later. We do this by having a restart record. The tree structure means we can't
	simply return a pointer to the node to continue processing at - we need to recursively redescend the tree until we reach the same
	position, whereupon we will continue. Also, because of the fact that the area being laid out into is potentially a completely different
	size, we need to recalculate widths etc, so at least part of the tree needs to be reprocessed when we restart.

	Accordingly, two ways to do this immediately suggest themselves. The first is to store the path down the tree so that we can quickly
	and efficiently skip whole areas of the tree that do not need reprocessing and redescend just the sections we need to. The second is to
	accept that we will reprocess the entire prefix of the tree each time, and just not actually do any work until we reach the exact
	box where we need to restart.

	We opt for the second one here, on the grounds that 1) it's easier to code, 2) it requires a constant amount of storage, and 3) that
	the trees we will be reprocessing will be relatively small. Should we ever need to revisit this decision, we can do so.
*/

enum { T, R, B, L };

/* === LAYOUT INLINE TEXT === */

typedef struct string_walker
{
	fz_context *ctx;
	hb_buffer_t *hb_buf;
	int rtl;
	const char *start;
	const char *end;
	const char *s;
	fz_font *base_font;
	int script;
	int language;
	int small_caps;
	fz_font *font;
	fz_font *next_font;
	hb_glyph_position_t *glyph_pos;
	hb_glyph_info_t *glyph_info;
	unsigned int glyph_count;
	int scale;
} string_walker;

static int quick_ligature_mov(fz_context *ctx, string_walker *walker, unsigned int i, unsigned int n, int unicode)
{
	unsigned int k;
	for (k = i + n + 1; k < walker->glyph_count; ++k)
	{
		walker->glyph_info[k-n] = walker->glyph_info[k];
		walker->glyph_pos[k-n] = walker->glyph_pos[k];
	}
	walker->glyph_count -= n;
	return unicode;
}

static int quick_ligature(fz_context *ctx, string_walker *walker, unsigned int i)
{
	if (walker->glyph_info[i].codepoint == 'f' && i + 1 < walker->glyph_count && !fz_font_flags(walker->font)->is_mono)
	{
		if (walker->glyph_info[i+1].codepoint == 'f')
		{
			if (i + 2 < walker->glyph_count && walker->glyph_info[i+2].codepoint == 'i')
			{
				if (fz_encode_character(ctx, walker->font, 0xFB03))
					return quick_ligature_mov(ctx, walker, i, 2, 0xFB03);
			}
			if (i + 2 < walker->glyph_count && walker->glyph_info[i+2].codepoint == 'l')
			{
				if (fz_encode_character(ctx, walker->font, 0xFB04))
					return quick_ligature_mov(ctx, walker, i, 2, 0xFB04);
			}
			if (fz_encode_character(ctx, walker->font, 0xFB00))
				return quick_ligature_mov(ctx, walker, i, 1, 0xFB00);
		}
		if (walker->glyph_info[i+1].codepoint == 'i')
		{
			if (fz_encode_character(ctx, walker->font, 0xFB01))
				return quick_ligature_mov(ctx, walker, i, 1, 0xFB01);
		}
		if (walker->glyph_info[i+1].codepoint == 'l')
		{
			if (fz_encode_character(ctx, walker->font, 0xFB02))
				return quick_ligature_mov(ctx, walker, i, 1, 0xFB02);
		}
	}
	return walker->glyph_info[i].codepoint;
}

static void init_string_walker(fz_context *ctx, string_walker *walker, hb_buffer_t *hb_buf, int rtl, fz_font *font, int script, int language, int small_caps, const char *text)
{
	walker->ctx = ctx;
	walker->hb_buf = hb_buf;
	walker->rtl = rtl;
	walker->start = text;
	walker->end = text;
	walker->s = text;
	walker->base_font = font;
	walker->script = script;
	walker->language = language;
	walker->font = NULL;
	walker->next_font = NULL;
	walker->small_caps = small_caps;
}

static void
destroy_hb_shaper_data(fz_context *ctx, void *handle)
{
	fz_hb_lock(ctx);
	hb_font_destroy(handle);
	fz_hb_unlock(ctx);
}

static const hb_feature_t small_caps_feature[1] = {
	{ HB_TAG('s','m','c','p'), 1, 0, (unsigned int)-1 }
};

static int walk_string(string_walker *walker)
{
	fz_context *ctx = walker->ctx;
	FT_Face face;
	int fterr;
	int quickshape;
	char lang[8];

	walker->start = walker->end;
	walker->end = walker->s;
	walker->font = walker->next_font;

	if (*walker->start == 0)
		return 0;

	/* Run through the string, encoding chars until we find one
	 * that requires a different fallback font. */
	while (*walker->s)
	{
		int c;

		walker->s += fz_chartorune(&c, walker->s);
		(void)fz_encode_character_with_fallback(ctx, walker->base_font, c, walker->script, walker->language, &walker->next_font);
		if (walker->next_font != walker->font)
		{
			if (walker->font != NULL)
				break;
			walker->font = walker->next_font;
		}
		walker->end = walker->s;
	}

	/* Disable harfbuzz shaping if script is common or LGC and there are no opentype tables. */
	quickshape = 0;
	if (walker->script <= 3 && !walker->rtl && !fz_font_flags(walker->font)->has_opentype)
		quickshape = 1;

	fz_hb_lock(ctx);
	fz_try(ctx)
	{
		face = fz_font_ft_face(ctx, walker->font);
		walker->scale = face->units_per_EM;
		fterr = FT_Set_Char_Size(face, walker->scale, walker->scale, 72, 72);
		if (fterr)
			fz_throw(ctx, FZ_ERROR_LIBRARY, "freetype setting character size: %s", ft_error_string(fterr));

		hb_buffer_clear_contents(walker->hb_buf);
		hb_buffer_set_direction(walker->hb_buf, walker->rtl ? HB_DIRECTION_RTL : HB_DIRECTION_LTR);
		/* hb_buffer_set_script(walker->hb_buf, hb_ucdn_script_translate(walker->script)); */
		if (walker->language)
		{
			fz_string_from_text_language(lang, walker->language);
			Memento_startLeaking(); /* HarfBuzz leaks harmlessly */
			hb_buffer_set_language(walker->hb_buf, hb_language_from_string(lang, (int)strlen(lang)));
			Memento_stopLeaking(); /* HarfBuzz leaks harmlessly */
		}
		hb_buffer_set_cluster_level(walker->hb_buf, HB_BUFFER_CLUSTER_LEVEL_CHARACTERS);

		hb_buffer_add_utf8(walker->hb_buf, walker->start, walker->end - walker->start, 0, -1);

		if (!quickshape)
		{
			fz_shaper_data_t *hb = fz_font_shaper_data(ctx, walker->font);
			Memento_startLeaking(); /* HarfBuzz leaks harmlessly */
			if (hb->shaper_handle == NULL)
			{
				hb->destroy = destroy_hb_shaper_data;
				hb->shaper_handle = hb_ft_font_create(face, NULL);
			}

			hb_buffer_guess_segment_properties(walker->hb_buf);

			if (walker->small_caps)
				hb_shape(hb->shaper_handle, walker->hb_buf, small_caps_feature, nelem(small_caps_feature));
			else
				hb_shape(hb->shaper_handle, walker->hb_buf, NULL, 0);
			Memento_stopLeaking();
		}

		walker->glyph_pos = hb_buffer_get_glyph_positions(walker->hb_buf, &walker->glyph_count);
		walker->glyph_info = hb_buffer_get_glyph_infos(walker->hb_buf, NULL);
	}
	fz_always(ctx)
	{
		fz_hb_unlock(ctx);
	}
	fz_catch(ctx)
	{
		fz_rethrow(ctx);
	}

	if (quickshape)
	{
		unsigned int i;
		for (i = 0; i < walker->glyph_count; ++i)
		{
			int glyph, unicode;
			unicode = quick_ligature(ctx, walker, i);
			if (walker->small_caps)
				glyph = fz_encode_character_sc(ctx, walker->font, unicode);
			else
				glyph = fz_encode_character(ctx, walker->font, unicode);
			walker->glyph_info[i].codepoint = glyph;
			walker->glyph_pos[i].x_offset = 0;
			walker->glyph_pos[i].y_offset = 0;
			walker->glyph_pos[i].x_advance = fz_advance_glyph(ctx, walker->font, glyph, 0) * face->units_per_EM;
			walker->glyph_pos[i].y_advance = 0;
		}
	}

	return 1;
}

static const char *get_node_text(fz_context *ctx, fz_html_flow *node)
{
	if (node->type == FLOW_WORD)
		return node->content.text;
	else if (node->type == FLOW_SPACE)
		return " ";
	else if (node->type == FLOW_SHYPHEN)
		return "-";
	else
		return "";
}

static void measure_string_w(fz_context *ctx, fz_html_flow *node, hb_buffer_t *hb_buf)
{
	float em = node->box->s.layout.em;
	string_walker walker;
	unsigned int i;
	const char *s;
	node->w = 0;
	s = get_node_text(ctx, node);
	init_string_walker(ctx, &walker, hb_buf, node->bidi_level & 1, node->box->style->font, node->script, node->markup_lang, node->box->style->small_caps, s);
	while (walk_string(&walker))
	{
		int x = 0;
		for (i = 0; i < walker.glyph_count; i++)
			x += walker.glyph_pos[i].x_advance;
		node->w += x * em / walker.scale;
	}
}

static void measure_string_h(fz_context *ctx, fz_html_flow *node)
{
	float em = node->box->s.layout.em;
	if (fz_css_number_defined(node->box->style->leading))
		node->h = fz_from_css_number(node->box->style->leading, em, em, 0);
	else
		node->h = fz_from_css_number_scale(node->box->style->line_height, em);
}


static float measure_line(fz_html_flow *node, fz_html_flow *end, float *baseline)
{
	float max_a = 0, max_d = 0, h = node->h;
	while (node != end)
	{
		if (node->type == FLOW_IMAGE)
		{
			if (node->h > max_a)
				max_a = node->h;
		}
		else if (node->type != FLOW_SBREAK && node->type != FLOW_BREAK)
		{
			// Clamp ascender/descender to line-height size.
			// TODO: This is not entirely to spec, but close enough.
			float s = fz_min(node->box->s.layout.em, node->h);
			float a = s * 0.8f;
			float d = s * 0.2f;
			if (a > max_a) max_a = a;
			if (d > max_d) max_d = d;
		}
		if (node->h > h)
			h = node->h;
		node = node->next;
	}
	*baseline = max_a + (h - max_a - max_d) / 2;
	return h;
}

static void layout_line(fz_context *ctx, float indent, float page_w, float line_w, int align, fz_html_flow *start, fz_html_flow *end, fz_html_box *box, float baseline, float line_h)
{
	float x = box->s.layout.x + indent;
	float y = box->s.layout.b;
	float slop = page_w - line_w;
	float justify = 0;
	float va;
	int n, i;
	fz_html_flow *node;
	fz_html_flow **reorder;
	unsigned int min_level, max_level;

	/* Count the number of nodes on the line */
	for(i = 0, n = 0, node = start; node != end; node = node->next)
	{
		n++;
		if (node->type == FLOW_SPACE && node->expand && !node->breaks_line)
			i++;
	}

	if (align == TA_JUSTIFY)
	{
		justify = slop / (i ? i : 1);
	}
	else if (align == TA_RIGHT)
		x += slop;
	else if (align == TA_CENTER)
		x += slop / 2;

	/* We need a block to hold the node pointers while we reorder */
	reorder = fz_malloc_array(ctx, n, fz_html_flow*);
	min_level = start->bidi_level;
	max_level = start->bidi_level;
	for(i = 0, node = start; node != end; i++, node = node->next)
	{
		reorder[i] = node;
		if (node->bidi_level < min_level)
			min_level = node->bidi_level;
		if (node->bidi_level > max_level)
			max_level = node->bidi_level;
	}

	/* Do we need to do any reordering? */
	if (min_level != max_level || (min_level & 1))
	{
		/* The lowest level we swap is always a rtl one */
		min_level |= 1;
		/* Each time around the loop we swap runs of fragments that have
		 * levels >= max_level (and decrement max_level). */
		do
		{
			int start_idx = 0;
			int end_idx;
			do
			{
				/* Skip until we find a level that's >= max_level */
				while (start_idx < n && reorder[start_idx]->bidi_level < max_level)
					start_idx++;
				/* If start >= n-1 then no more runs. */
				if (start_idx >= n-1)
					break;
				/* Find the end of the match */
				i = start_idx+1;
				while (i < n && reorder[i]->bidi_level >= max_level)
					i++;
				/* Reverse from start to i-1 */
				end_idx = i-1;
				while (start_idx < end_idx)
				{
					fz_html_flow *t = reorder[start_idx];
					reorder[start_idx++] = reorder[end_idx];
					reorder[end_idx--] = t;
				}
				start_idx = i+1;
			}
			while (start_idx < n);
			max_level--;
		}
		while (max_level >= min_level);
	}

	for (i = 0; i < n; i++)
	{
		float w;

		node = reorder[i];
		w = node->w;

		if (node->type == FLOW_SPACE && node->breaks_line)
			w = 0;
		else if (node->type == FLOW_SPACE && !node->breaks_line)
			w += node->expand ? justify : 0;
		else if (node->type == FLOW_SHYPHEN && !node->breaks_line)
			w = 0;
		else if (node->type == FLOW_SHYPHEN && node->breaks_line)
			w = node->w;

		node->x = x;
		x += w;

		switch (node->box->style->vertical_align)
		{
		default:
		case VA_BASELINE:
		case VA_SUB:
		case VA_SUPER:
			va = node->box->s.layout.baseline;
			break;

		case VA_TOP:
		case VA_TEXT_TOP:
			va = -baseline + node->box->s.layout.em * 0.8f;
			break;
		case VA_BOTTOM:
		case VA_TEXT_BOTTOM:
			va = -baseline + line_h - node->box->s.layout.em * 0.2f;
			break;
		}

		if (node->type == FLOW_IMAGE)
			node->y = y + baseline - node->h;
		else
		{
			node->y = y + baseline + va;
			node->h = node->box->s.layout.em;
		}
	}

	fz_free(ctx, reorder);
}

typedef struct
{
	fz_pool *pool;
	float page_top;
	float page_h;
	hb_buffer_t *hb_buf;
	fz_html_restarter *restart;
} layout_data;

static int flush_line(fz_context *ctx, fz_html_box *box, layout_data *ld, float page_w, float line_w, int align, float indent, fz_html_flow *a, fz_html_flow *b, fz_html_restarter *restart)
{
	float avail, line_h, baseline;
	float page_h = ld->page_h;
	float page_top = ld->page_top;
	line_h = measure_line(a, b, &baseline);
	if (page_h > 0)
	{
		avail = page_h - fmodf(box->s.layout.b - page_top, page_h);
		/* If the line is larger than the available space skip to the start
		 * of the next page. */
		if (line_h > avail)
		{
			if (restart)
			{
				assert(restart->start == NULL);

				if (restart->potential)
					restart->end = restart->potential;
				else
				{
					restart->end = box;
					restart->end_flow = a;
				}
				restart->reason = FZ_HTML_RESTART_REASON_LINE_HEIGHT;
				return 1;
			}
			box->s.layout.b += avail;
		}
	}
	layout_line(ctx, indent, page_w, line_w, align, a, b, box, baseline, line_h);
	box->s.layout.b += line_h;
	if (restart)
		restart->potential = NULL;

	return 0;
}

static void break_word_for_overflow_wrap(fz_context *ctx, fz_html_flow *node, layout_data *ld)
{
	hb_buffer_t *hb_buf = ld->hb_buf;
	const char *text = node->content.text;
	string_walker walker;

	assert(node->type == FLOW_WORD);
	assert(node->atomic == 0);

	/* Split a word node after the first cluster (usually a character), and
	 * flag the second half as a valid node to break before if in desperate
	 * need. This may break earlier than necessary, but in that case we'll
	 * break the second half again when we come to it, until we find a
	 * suitable breaking point.
	 *
	 * We split after each clusters here so we can flag each fragment as
	 * "atomic" so we don't try breaking it again, and also to flag the
	 * following word fragment as a possible break point. Breaking at the
	 * exact desired point would make this more complicated than necessary.
	 *
	 * Desperately breaking in the middle of a word like this should should
	 * rarely (if ever) come up.
	 *
	 * TODO: Split at all the clusters in the word at once.
	 */

	/* Walk string and split at the first cluster. */
	init_string_walker(ctx, &walker, hb_buf, node->bidi_level & 1, node->box->style->font, node->script, node->markup_lang, node->box->style->small_caps, text);
	while (walk_string(&walker))
	{
		unsigned int i, a, b;
		a = walker.glyph_info[0].cluster;
		for (i = 0; i < walker.glyph_count; ++i)
		{
			b = walker.glyph_info[i].cluster;
			if (b != a)
			{
				fz_html_split_flow(ctx, ld->pool, node, fz_runeidx(text, text + b));
				node->atomic = 1;
				node->next->overflow_wrap = 1;
				measure_string_w(ctx, node, ld->hb_buf);
				measure_string_w(ctx, node->next, ld->hb_buf);
				return;
			}
		}
	}

	/* Word is already only one cluster. Don't try breaking here again! */
	node->atomic = 1;
}

/*
	Layout a BOX_FLOW.

	Flow box is in a BOX_BLOCK or BOX_TABLE_CELL context, and has no margin/padding/border.

	box: The BOX_FLOW to layout.
	top: The enclosing box.
*/
static void layout_flow(fz_context *ctx, layout_data *ld, fz_html_box *box, fz_html_box *top)
{
	fz_html_flow *node, *line, *candidate, *desperate;
	fz_html_flow *start_flow = NULL;
	float line_w, candidate_w, desperate_w, indent;
	int align;
	fz_html_restarter *restart = ld->restart;

	float em = box->s.layout.em;
	indent = box->is_first_flow ? fz_from_css_number(top->style->text_indent, em, top->s.layout.w, 0) : 0;
	align = top->style->text_align;

	if (box->markup_dir == FZ_BIDI_RTL)
	{
		if (align == TA_LEFT)
			align = TA_RIGHT;
		else if (align == TA_RIGHT)
			align = TA_LEFT;
	}

	/* Position the box, initially zero height. */
	box->s.layout.x = top->s.layout.x;
	box->s.layout.y = top->s.layout.b;
	box->s.layout.w = top->s.layout.w;
	box->s.layout.b = box->s.layout.y;

	if (restart && restart->start)
	{
		/* If we are still skipping, and don't match, nothing to do. */
		if (restart->start != box)
			return;
		/* We match! Remember where we should start. */
		restart->start = NULL;

#ifdef DEBUG_LAYOUT_RESTARTING
		/* Output us some crufty debug */
		if (restart->start_flow == NULL)
			printf("<restart>");
		for (node = box->u.flow.head; node; node = node->next)
		{
			if (restart->start_flow == node)
				printf("<restart>");
			switch (node->type)
			{
			case FLOW_WORD:
				printf("[%s]", node->content.text);
				break;
			case FLOW_BREAK:
			case FLOW_SBREAK:
				printf("\n");
				break;
			case FLOW_SPACE:
				printf(" ");
				break;
			case FLOW_SHYPHEN:
				printf("-");
				break;
			default:
				printf("?");
				break;
			}
		}
		printf("\n");
#endif
	}

	/* If we have nothing to flow, nothing to do. */
	if (!box->u.flow.head)
		return;

	/* Measure the size of all the words and images in the flow. */
	node = box->u.flow.head;

	/* First, if we are restarting, skip over ones we've done already. */
	if (restart && restart->start_flow)
	{
		while(node && node != restart->start_flow)
		{
			indent = 0;
			node = node->next;
		}
		start_flow = node;
		restart->start_flow = NULL;
	}

	/* Now measure the size of the remaining nodes. */
	for (; node; node = node->next)
	{
		node->breaks_line = 0; /* reset line breaks from previous layout */

		if (node->type == FLOW_IMAGE)
		{
			float max_w, max_h;
			float xs = 1, ys = 1, s;
			float aspect = 1;

			max_w = top->s.layout.w;
			max_h = ld->page_h;

			/* NOTE: We ignore the image DPI here, since most images in EPUB files have bogus values. */
			node->w = node->content.image->w * 72.0f / 96.0f;
			node->h = node->content.image->h * 72.0f / 96.0f;
			aspect = node->h ? node->w / node->h : 0;

			if (node->box->style->width.unit != N_AUTO)
				node->w = fz_from_css_number(node->box->style->width, top->s.layout.em, top->s.layout.w, node->w);
			if (node->box->style->height.unit != N_AUTO)
				node->h = fz_from_css_number(node->box->style->height, top->s.layout.em, ld->page_h, node->h);
			if (node->box->style->width.unit == N_AUTO && node->box->style->height.unit != N_AUTO)
				node->w = node->h * aspect;
			if (node->box->style->width.unit != N_AUTO && node->box->style->height.unit == N_AUTO)
				node->h = (aspect == 0) ? 0 : (node->w / aspect);

			/* Shrink image to fit on one page if needed */
			if (max_w > 0 && node->w > max_w)
				xs = max_w / node->w;
			if (max_h > 0 && node->h > max_h)
				ys = max_h / node->h;
			s = fz_min(xs, ys);
			node->w = node->w * s;
			node->h = node->h * s;

		}
		else
		{
			/* Note: already measured width in layout_update_widths */
			measure_string_h(ctx, node);
		}
	}

	node = box->u.flow.head;
	if (start_flow)
	{
		line_w = start_flow == node ? indent : 0;
		node = start_flow;
	}
	else
	{
		line_w = indent;
	}
	line = node;

	candidate = NULL;
	candidate_w = 0;
	desperate = NULL;
	desperate_w = 0;

	/* Now collate the measured nodes into a line. */
	while (node)
	{

		switch (node->type)
		{
		default:
			// always same width
			line_w += node->w;
			break;

		case FLOW_WORD:
			/* Allow desperate breaking in middle of word if overflow-wrap: break-word. */
			if (line_w + node->w > box->s.layout.w && !candidate)
			{
				if (!node->atomic && node->box->style->overflow_wrap == OVERFLOW_WRAP_BREAK_WORD)
				{
					break_word_for_overflow_wrap(ctx, node, ld);
				}
			}
			/* Remember overflow-wrap word fragments, unless at the beginning of a line. */
			if (node->overflow_wrap && node != line)
			{
				desperate = node;
				desperate_w = line_w;
			}
			line_w += node->w;
			break;

		case FLOW_BREAK:
		case FLOW_SBREAK:
			// always zero width
			candidate = node;
			candidate_w = line_w;
			break;

		case FLOW_SPACE:
			// zero width if broken, default width if unbroken
			candidate = node;
			candidate_w = line_w;
			line_w += node->w;
			break;

		case FLOW_SHYPHEN:
			// default width if broken, zero width if unbroken
			candidate = node;
			candidate_w = line_w + node->w;
			break;
		}

		/* If we see a hard break...
		 * or the line doesn't fit, and we have a candidate breakpoint...
		 * then we can flush the line so far. */
		if (node->type == FLOW_BREAK || (line_w > box->s.layout.w && (candidate || desperate)))
		{
			int line_align = align;
			fz_html_flow *break_at;
			float break_w;

			if (candidate)
			{
				if (candidate->type == FLOW_BREAK)
					line_align = (align == TA_JUSTIFY) ? TA_LEFT : align;
				candidate->breaks_line = 1;
				break_at = candidate->next;
				break_w = candidate_w;
			}
			else
			{
				break_at = desperate;
				break_w = desperate_w;
			}

			if (flush_line(ctx, box, ld, box->s.layout.w, break_w, line_align, indent, line, break_at, restart))
				return;

			line = break_at;
			node = break_at;
			candidate = NULL;
			candidate_w = 0;
			desperate = NULL;
			desperate_w = 0;
			indent = 0;
			line_w = 0;
		}
		else if (restart && (restart->flags & FZ_HTML_RESTARTER_FLAGS_NO_OVERFLOW) && line_w > box->s.layout.w)
		{
			/* We are in 'no-overflow' mode, and the line doesn't fit.
			 * This means our first box is too wide to ever fit in a box of this width. */
			assert(restart->start == NULL);

			restart->end = box;
			restart->end_flow = start_flow;
			restart->reason = FZ_HTML_RESTART_REASON_LINE_WIDTH;
			return;
		}
		else
		{
			node = node->next;
		}
	}

	if (line)
	{
		int line_align = (align == TA_JUSTIFY) ? TA_LEFT : align;
		flush_line(ctx, box, ld, box->s.layout.w, line_w, line_align, indent, line, NULL, restart);
	}
}

static float advance_for_spacing(fz_context *ctx, layout_data *ld, float start_b, float spacing, int *eop)
{
	float page_h = ld->page_h;
	float page_top = ld->page_top;
	float avail = page_h - fmodf(start_b - page_top, page_h);
	if (spacing > avail)
	{
		*eop = 1;
		spacing = avail;
	}
	return start_b + spacing;
}

static int layout_block_page_break(fz_context *ctx, layout_data *ld, float *yp, int page_break)
{
	float page_h = ld->page_h;
	float page_top = ld->page_top;
	if (page_h <= 0)
		return 0;
	if (page_break == PB_ALWAYS || page_break == PB_LEFT || page_break == PB_RIGHT)
	{
		float avail = page_h - fmodf(*yp - page_top, page_h);
		int number = (*yp + (page_h * 0.1f)) / page_h;
		if (avail > 0 && avail < page_h)
		{
			*yp += avail;
			if (page_break == PB_LEFT && (number & 1) == 0) /* right side pages are even */
				*yp += page_h;
			if (page_break == PB_RIGHT && (number & 1) == 1) /* left side pages are odd */
				*yp += page_h;
			return 1;
		}
	}
	return 0;
}

static void layout_block(fz_context *ctx, layout_data *ld, fz_html_box *box, fz_html_box *top);
static void layout_table(fz_context *ctx, layout_data *ld, fz_html_box *box, fz_html_box *top);

/* === LAYOUT TABLE === */

// TODO: apply CSS from colgroup and col definition to table cells
// TODO: use CSS border-collapse on table
// TODO: use CSS/HTML column-span/colspan on table-cell
// TODO: use CSS/HTML width on table-cell when computing maximum width

struct column_width {
	float min, max, actual;
};

static float table_cell_padding(fz_context *ctx, fz_html_box *box)
{
	return (
		box->u.block.padding[L] + box->u.block.border[L] +
		box->u.block.padding[R] + box->u.block.border[R]
	);
}

static float block_padding(fz_context *ctx, fz_html_box *box)
{
	return (
		box->u.block.padding[L] + box->u.block.border[L] + box->u.block.margin[L] +
		box->u.block.padding[R] + box->u.block.border[R] + box->u.block.margin[R]
	);
}

static float largest_min_width(fz_context *ctx, fz_html_box *box)
{
	/* The "minimum" width is the largest word in a paragraph. */
	float r_min = 0;
	if (box->type == BOX_BLOCK)
	{
		fz_html_box *child = box->down;
		while (child)
		{
			float min = largest_min_width(ctx, child);
			if (min > r_min)
				r_min = min;
			child = child->next;
		}
		r_min += block_padding(ctx, box);
	}
	else if (box->type == BOX_FLOW)
	{
		fz_html_flow *flow;
		for (flow = box->u.flow.head; flow; flow = flow->next)
			if (flow->w > r_min)
				r_min = flow->w;
	}
	else
	{
		// TODO: nested TABLE
	}
	return r_min;
}

static float largest_max_width(fz_context *ctx, fz_html_box *box)
{
	/* The "maximum" width is the length of the longest paragraph laid out on one line. */
	float r_max = 0;
	if (box->type == BOX_BLOCK)
	{
		fz_html_box *child = box->down;
		while (child)
		{
			float max = largest_max_width(ctx, child);
			if (max > r_max)
				r_max = max;
			child = child->next;
		}
		r_max += block_padding(ctx, box);
	}
	else if (box->type == BOX_FLOW)
	{
		fz_html_flow *flow;
		float max = 0;
		for (flow = box->u.flow.head; flow; flow = flow->next)
		{
			max += flow->w;
			if (flow->type == FLOW_BREAK)
			{
				if (max > r_max)
					r_max = max;
				max = 0;
			}
		}
		if (max > r_max)
			r_max = max;
	}
	else
	{
		// TODO: nested TABLE
	}
	return r_max;
}

static void squish_block(fz_context *ctx, fz_html_box *box)
{
	fz_html_box *child;

	box->s.layout.b = box->s.layout.y;
	if (box->type == BOX_FLOW)
		return;
	for (child = box->down; child; child = child->next)
		squish_block(ctx, child);
}

static void layout_table_row(fz_context *ctx, layout_data *ld, fz_html_box *row, int ncol, struct column_width *colw, float spacing)
{
	fz_html_box *cell, *child;
	int col = 0;
	float x = row->s.layout.x;
	float y;

	/* Always layout the full row since we can't restart in the middle of a cell.
	 * If the row doesn't fit fully, we'll postpone it to the next page.
	 * FIXME: If the row doesn't fit then either, we should split it with the offset.
	 */
	fz_html_restarter *save_restart = ld->restart;
	ld->restart = NULL;

	/* Note: margin is ignored for table cells and rows */

	/* For each cell in the row */
	for (cell = row->down; cell; cell = cell->next)
	{
		float cell_pad = table_cell_padding(ctx, cell);

		x += spacing;

		/* Position the cell */
		cell->s.layout.y = row->s.layout.y;
		cell->s.layout.x = x;
		cell->s.layout.w = colw[col].actual - cell_pad;

		/* Adjust content box */
		cell->s.layout.x += cell->u.block.padding[L] + cell->u.block.border[L];
		cell->s.layout.y += cell->u.block.padding[T] + cell->u.block.border[T];
		cell->s.layout.b = cell->s.layout.y;

		/* Layout cell contents into the cell. */
		for (child = cell->down; child; child = child->next)
		{
			if (child->type == BOX_BLOCK)
			{
				layout_block(ctx, ld, child, cell);
				cell->s.layout.b = child->s.layout.b;
				cell->s.layout.b += child->u.block.padding[B] + child->u.block.border[B] + child->u.block.margin[B];
			}
			else if (child->type == BOX_TABLE)
			{
				layout_table(ctx, ld, child, cell);
				cell->s.layout.b = child->s.layout.b;
				cell->s.layout.b += child->u.block.padding[B] + child->u.block.border[B] + child->u.block.margin[B];
			}
			else if (child->type == BOX_FLOW)
			{
				layout_flow(ctx, ld, child, cell);
				cell->s.layout.b = child->s.layout.b;
			}
		}

		/* Advance to next column */
		x += colw[col].actual;

		/* Adjust row height if necessary */
		y = cell->s.layout.b + cell->u.block.padding[B] + cell->u.block.border[B];
		if (y > row->s.layout.b)
			row->s.layout.b = y;

		++col;
	}

	/* For each cell in the row - adjust final cell heights to fill the row */
	for (cell = row->down; cell; cell = cell->next)
	{
		cell->s.layout.b = row->s.layout.b - (cell->u.block.padding[B] + cell->u.block.border[B]);
	}

	ld->restart = save_restart;
}

static void layout_table(fz_context *ctx, layout_data *ld, fz_html_box *box, fz_html_box *top)
{
	fz_html_box *row;
	int col, ncol = 0;
	float min_tabw, max_tabw;
	struct column_width *colw;
	fz_html_restarter *restart = ld->restart;
	float spacing;
	int eop = 0;

	float em = box->s.layout.em;
	float *margin = box->u.block.margin;
	float *border = box->u.block.border;
	float *padding = box->u.block.padding;
	float auto_w;

	spacing = fz_from_css_number(box->style->border_spacing, box->s.layout.em, box->s.layout.w, 0);

	if (restart)
	{
		/* We have reached the restart point */
		if (restart->start == box)
			restart->start = NULL;
	}

	/* TODO: remove 'vertical' margin adjustments across automatic page breaks */
	if (restart && restart->start != NULL)
	{
		/* We're still skipping, don't check for pagebreak before! */
	}
	else if (layout_block_page_break(ctx, ld, &top->s.layout.b, box->style->page_break_before))
		eop = 1;

	/* Position table in box flow, and add margins and padding */
	box->s.layout.y = advance_for_spacing(ctx, ld, top->s.layout.b, margin[T] + border[T] + padding[T], &eop);

	if (eop)
	{
		if (restart && restart->end == NULL)
		{
			box->s.layout.b = box->s.layout.y;
			if (restart->potential)
				restart->end = restart->potential;
			else
				restart->end = box;
			return;
		}
	}

	/* Finalize position and width. */
	auto_w = top->s.layout.w - (margin[L] + margin[R] + border[L] + border[R] + padding[L] + padding[R]);
	box->s.layout.x = top->s.layout.x + margin[L] + border[L] + padding[L];
	box->s.layout.w = fz_from_css_number(box->style->width, em, auto_w, auto_w);

	/* Add initial border-spacing */
	box->s.layout.b = box->s.layout.y + spacing;

	/* Find the maximum number of columns. (Count 'col' for each row, biggest one gives ncol). */
	for (row = box->down; row; row = row->next)
	{
		fz_html_box *cell;
		col = 0;
		for (cell = row->down; cell; cell = cell->next)
			++col;
		if (col > ncol)
			ncol = col;
	}

	colw = fz_malloc_array(ctx, ncol, struct column_width);

	// TODO: colgroups and colspan

	fz_try(ctx)
	{
		/* Table Autolayout algorithm from HTML */
		/* https://www.w3.org/TR/REC-html40/appendix/notes.html#h-B.5.2 */

		/* Calculate largest minimum and maximum column widths */
		for (col = 0; col < ncol; ++col)
		{
			colw[col].min = 0;
			colw[col].max = 0;
		}

		for (row = box->down; row; row = row->next)
		{
			fz_html_box *cell, *child;
			for (col = 0, cell = row->down; cell; cell = cell->next, ++col)
			{
				float cell_pad = table_cell_padding(ctx, cell);
				for (child = cell->down; child; child = child->next)
				{
					float min = largest_min_width(ctx, child) + cell_pad;
					float max = largest_max_width(ctx, child) + cell_pad;
					if (min > colw[col].min)
						colw[col].min = min;
					if (max > colw[col].max)
						colw[col].max = max;
				}
			}
		}

		min_tabw = max_tabw = 0;
		for (col = 0; col < ncol; ++col)
		{
			min_tabw += colw[col].min;
			max_tabw += colw[col].max;
		}
		min_tabw += spacing * (ncol + 1);
		max_tabw += spacing * (ncol + 1);

		/* The minimum table width is equal to or wider than the available space.
		 * In this case, assign the minimum widths and let the lines overflow...
		 */
		if (min_tabw >= box->s.layout.w)
		{
			for (col = 0; col < ncol; ++col)
				colw[col].actual = colw[col].min;
		}

		/* The maximum table width fits within the available space.
		 * In this case, set the columns to their maximum widths.
		 */
		else if (max_tabw <= box->s.layout.w)
		{
			box->s.layout.w = max_tabw;
			for (col = 0; col < ncol; ++col)
				colw[col].actual = colw[col].max;
		}

		/* The maximum width of the table is greater than the available space, but
		 * the minimum table width is smaller. In this case, find the difference
		 * between the available space and the minimum table width, lets call it
		 * W. Lets also call D the difference between maximum and minimum width of
		 * the table.
		 *
		 * For each column, let d be the difference between maximum and minimum
		 * width of that column. Now set the column's width to the minimum width
		 * plus d times W over D. This makes columns with large differences
		 * between minimum and maximum widths wider than columns with smaller
		 * differences.
		 */
		else
		{
			float W = (box->s.layout.w - min_tabw);
			float D = (max_tabw - min_tabw);
			for (col = 0; col < ncol; ++col)
				colw[col].actual = colw[col].min + (colw[col].max - colw[col].min) * W / D;
		}

		/* Layout each row in turn. */
		for (row = box->down; row; row = row->next)
		{
			/* Position the row, zero height for now. */
			row->s.layout.x = box->s.layout.x;
			row->s.layout.w = box->s.layout.w;
			row->s.layout.y = row->s.layout.b = box->s.layout.b;
			row->s.layout.b = row->s.layout.y;

			if (restart && restart->start != NULL)
			{
				if (restart->start == row)
					restart->start = NULL;
				else
				{
					squish_block(ctx, row);
					continue; /* still skipping */
				}
			}

			layout_table_row(ctx, ld, row, ncol, colw, spacing);

			/* If the row doesn't fit on the current page, break here and put the row on the next page.
			 * Unless the row was at the very start of the page, in which case it'll overflow instead.
			 * FIXME: Don't overflow, draw twice with offset to break it abruptly at the page border!
			 */
			if (ld->page_h > 0)
			{
				float avail = ld->page_h - fmodf(row->s.layout.y - ld->page_top, ld->page_h);
				float used = row->s.layout.b - row->s.layout.y;
				if (used > avail && avail < ld->page_h)
				{
					if (restart)
					{
						restart->end = row;
						goto exit;
					}
					else
					{
						row->s.layout.y += avail;
						layout_table_row(ctx, ld, row, ncol, colw, spacing);
					}
				}
			}

			box->s.layout.b = row->s.layout.b + spacing;
		}
		exit:;
	}
	fz_always(ctx)
		fz_free(ctx, colw);
	fz_catch(ctx)
		fz_rethrow(ctx);

	if (restart && restart->start != NULL)
	{
		/* We're still skipping, don't check for pagebreak after! */
	}
	else if (layout_block_page_break(ctx, ld, &top->s.layout.b, box->style->page_break_after))
	{
		if (restart && restart->end == NULL)
		{
			if (restart->potential)
				restart->end = restart->potential;
			else
				restart->end = box;
			return;
		}
	}
}

/* === LAYOUT BLOCKS === */

/*
	Layout a BOX_BLOCK.

	ctx: The ctx in use.
	box: The BOX_BLOCK to layout.
	top_x: The x position for left of the topmost box.
	top_b: Pointer to the y position for the top of the topmost box on entry, updated to the y position for the bottom of the topmost box on exit.
	top_w: The width available for the topmost box.
*/
static void layout_block(fz_context *ctx, layout_data *ld, fz_html_box *box, fz_html_box *top)
{
	fz_html_box *child;
	fz_html_restarter *restart = ld->restart;

	const fz_css_style *style = box->style;
	float em = box->s.layout.em;
	float *margin = box->u.block.margin;
	float *border = box->u.block.border;
	float *padding = box->u.block.padding;
	float auto_w;
	int eop = 0;

	assert(fz_html_box_has_boxes(box));

	/* If restart is non-NULL, we are running in restartable mode. */
	if (restart)
	{
		/* If restart->start == box, then we've been skipping, and this
		 * is the point at which we should restart. */
		if (restart->start == box)
		{
			/* Set restart->start to be NULL to indicate that we aren't skipping
			 * any more. */
			restart->start = NULL;
		}

		/* In the event that no content fits, we want to restart with us, not with the
		 * content that doesn't fit. */
		if (restart->potential == NULL)
			restart->potential = box;
	}

	/* TODO: remove 'vertical' margin adjustments across automatic page breaks */
	if (restart && restart->start != NULL)
	{
		/* We're still skipping, don't check for pagebreak before! */
	}
	else if (layout_block_page_break(ctx, ld, &top->s.layout.b, style->page_break_before))
		eop = 1;

	/* Important to remember that box->{x,y,w,b} are the coordinates of the content. The
	 * margin/border/paddings are all outside this. */
	box->s.layout.y = top->s.layout.b;
	if (restart && restart->start != NULL)
	{
		/* We're still skipping, so any child should inherit 0 vertical margin from us. */
	}
	else
	{
		/* We're not skipping, so add in the spacings to the top edge of our box. */
		box->s.layout.y = advance_for_spacing(ctx, ld, box->s.layout.y, margin[T] + border[T] + padding[T], &eop);
	}
	if (eop)
	{
		if (restart && restart->end == NULL)
		{
			box->s.layout.b = box->s.layout.y;
			if (restart->potential)
				restart->end = restart->potential;
			else
				restart->end = box;
			return;
		}
	}

	/* Finalize position and width. */
	auto_w = top->s.layout.w - (margin[L] + margin[R] + border[L] + border[R] + padding[L] + padding[R]);
	box->s.layout.x = top->s.layout.x + margin[L] + border[L] + padding[L];
	box->s.layout.w = fz_from_css_number(box->style->width, em, auto_w, auto_w);

	/* Start with our content being zero height. */
	box->s.layout.b = box->s.layout.y;

	for (child = box->down; child; child = child->next)
	{
		if (restart && restart->end == NULL)
		{
			/* If advancing over the bottom margin/border/padding of a child has previously
			 * brought us to the end of a page, this is where we end. */
			if (eop)
			{
				if (restart->potential)
					restart->end = restart->potential;
				else
					restart->end = child;
				break;
			}
		}

		if (child->type == BOX_BLOCK || child->type == BOX_TABLE)
		{
			assert(fz_html_box_has_boxes(child));
			if (child->type == BOX_BLOCK)
				layout_block(ctx, ld, child, box);
			else
				layout_table(ctx, ld, child, box);

			/* Unless we're still skipping, the base of our box must now be at least as
			 * far down as the child, plus the child's spacing. */
			if (!restart || restart->start == NULL)
			{
				box->s.layout.b = advance_for_spacing(ctx, ld,
					child->s.layout.b,
					child->u.block.padding[B] + child->u.block.border[B] + child->u.block.margin[B],
					&eop);
			}
		}

		else if (child->type == BOX_FLOW)
		{
			layout_flow(ctx, ld, child, box);
			if (child->s.layout.b > child->s.layout.y)
			{
				if (!restart || restart->start == NULL)
				{
					box->s.layout.b = child->s.layout.b;
				}
			}
		}

		/* Stop if we've reached the endpoint. */
		if (restart && restart->end != NULL)
			break;
		if (restart && box->s.layout.b != box->s.layout.y)
			restart->potential = NULL;
	}

	/* If we're still skipping, exit with vertical=0. */
	/* If we've reached the endpoint, exit. */
	if (restart && (restart->start != NULL || restart->end != NULL))
		return;

	/* reserve space for the list mark */
	if (box->list_item && box->s.layout.y == box->s.layout.b)
	{
		box->s.layout.b += fz_from_css_number_scale(style->line_height, em);
	}

	if (restart && restart->start != NULL)
	{
		/* We're still skipping, don't check for pagebreak after! */
	}
	else if (layout_block_page_break(ctx, ld, &box->s.layout.b, style->page_break_after))
	{
		if (restart && restart->end == NULL)
		{
			if (restart->potential)
				restart->end = restart->potential;
			else
				restart->end = box;
			return;
		}
	}
}

/* === LAYOUT === */

// Compute new em, padding, border, margin.
// Also compute layout x and w.
static void layout_update_styles(fz_context *ctx, fz_html_box *box, fz_html_box *top)
{
	float top_em = top->s.layout.em;
	float top_baseline = top->s.layout.baseline;
	float top_w = top->s.layout.w;
	while (box)
	{
		const fz_css_style *style = box->style;
		float em = box->s.layout.em = fz_from_css_number(style->font_size, top_em, top_em, top_em);

		if (style->vertical_align == VA_SUPER)
			box->s.layout.baseline = top_baseline - top_em / 3;
		else if (style->vertical_align == VA_SUB)
			box->s.layout.baseline = top_baseline + top_em / 5;
		else
			box->s.layout.baseline = top_baseline;

		if (box->type != BOX_INLINE && box->type != BOX_FLOW)
		{
			float *margin = box->u.block.margin;
			float *border = box->u.block.border;
			float *padding = box->u.block.padding;

			margin[T] = fz_from_css_number(style->margin[T], em, top_w, 0);
			margin[R] = fz_from_css_number(style->margin[R], em, top_w, 0);
			margin[B] = fz_from_css_number(style->margin[B], em, top_w, 0);
			margin[L] = fz_from_css_number(style->margin[L], em, top_w, 0);

			padding[T] = fz_from_css_number(style->padding[T], em, top_w, 0);
			padding[R] = fz_from_css_number(style->padding[R], em, top_w, 0);
			padding[B] = fz_from_css_number(style->padding[B], em, top_w, 0);
			padding[L] = fz_from_css_number(style->padding[L], em, top_w, 0);

			border[T] = style->border_style_0 ? fz_from_css_number(style->border_width[T], em, top_w, 0) : 0;
			border[R] = style->border_style_1 ? fz_from_css_number(style->border_width[R], em, top_w, 0) : 0;
			border[B] = style->border_style_2 ? fz_from_css_number(style->border_width[B], em, top_w, 0) : 0;
			border[L] = style->border_style_3 ? fz_from_css_number(style->border_width[L], em, top_w, 0) : 0;

			// TODO: BLOCK nested inside TABLE!
			if (box->type == BOX_BLOCK || box->type == BOX_TABLE)
			{
				/* Compute preliminary width (will be adjusted if block is nested in table cell later) */
				float auto_w = top_w - (margin[L] + margin[R] + border[L] + border[R] + padding[L] + padding[R]);
				box->s.layout.w = fz_from_css_number(box->style->width, em, auto_w, auto_w);
			}
		}

		else if (box->type == BOX_FLOW)
		{
			box->s.layout.x = top->s.layout.x;
			box->s.layout.w = top->s.layout.w;
		}

		if (box->down)
			layout_update_styles(ctx, box->down, box);

		box = box->next;
	}
}

static void layout_update_widths(fz_context *ctx, fz_html_box *box, fz_html_box *top, hb_buffer_t *hb_buf)
{
	while (box)
	{
		if (box->type == BOX_FLOW)
		{
			fz_html_flow *node;

			for (node = box->u.flow.head; node; node = node->next)
			{
				if (node->type == FLOW_IMAGE)
					/* start with "native" size (only used for table width calculations) */
					node->w = node->content.image->w * 72.0f / 96.0f;
				else if (node->type == FLOW_WORD || node->type == FLOW_SPACE || node->type == FLOW_SHYPHEN)
					measure_string_w(ctx, node, hb_buf);
			}
		}

		if (box->down)
			layout_update_widths(ctx, box->down, box, hb_buf);

		box = box->next;
	}
}

static int is_layout_box(fz_html_box *box)
{
	return box->type == BOX_BLOCK || box->type == BOX_TABLE;
}

static int is_empty_block_box(fz_html_box *box)
{
	fz_html_box *child;
	if (box->type == BOX_BLOCK)
	{
		if (box->u.block.padding[T] != 0 || box->u.block.padding[B] != 0)
			return 0;
		if (box->u.block.border[T] != 0 || box->u.block.border[B] != 0)
			return 0;
		for (child = box->down; child; child = child->next)
		{
			if (child->type != BOX_BLOCK)
				return 0;
			if (!is_empty_block_box(child))
				return 0;
			if (child->u.block.margin[T] != 0 || child->u.block.margin[B] != 0)
				return 0;
		}
		return 1;
	}
	return 0;
}

static void layout_collapse_margin_with_children(fz_context *ctx, fz_html_box *here)
{
	fz_html_box *child, *first, *last = NULL;

	first = here->down;
	for (child = here->down; child; child = child->next)
	{
		layout_collapse_margin_with_children(ctx, child);
		last = child;
	}

	if (is_layout_box(here))
	{
		if (first && is_layout_box(first))
		{
			if (first->u.block.border[T] == 0 && first->u.block.padding[T] == 0)
			{
				float m = fz_max(first->u.block.margin[T], here->u.block.margin[T]);
				here->u.block.margin[T] = m;
				first->u.block.margin[T] = 0;
			}
		}

		if (last && is_layout_box(last))
		{
			if (last->u.block.border[T] == 0 && last->u.block.padding[T] == 0)
			{
				float m = fz_max(last->u.block.margin[B], here->u.block.margin[B]);
				here->u.block.margin[B] = m;
				last->u.block.margin[B] = 0;
			}
		}
	}
}

static void layout_collapse_margin_with_siblings(fz_context *ctx, fz_html_box *here)
{
	while (here)
	{
		fz_html_box *next = here->next;

		if (here->down)
			layout_collapse_margin_with_siblings(ctx, here->down);

		if (is_layout_box(here) && next && is_layout_box(next))
		{
			float m = fz_max(here->u.block.margin[B], next->u.block.margin[T]);
			here->u.block.margin[B] = m;
			next->u.block.margin[T] = 0;
		}

		here = next;
	}
}

static void layout_collapse_margin_with_self(fz_context *ctx, fz_html_box *here)
{
	while (here)
	{
		if (here->down)
			layout_collapse_margin_with_self(ctx, here->down);

		if (is_layout_box(here) && is_empty_block_box(here))
		{
			float m = fz_max(here->u.block.margin[T], here->u.block.margin[B]);
			here->u.block.margin[T] = 0;
			here->u.block.margin[B] = m;
		}

		here = here->next;
	}
}

static void layout_collapse_margins(fz_context *ctx, fz_html_box *box, fz_html_box *top)
{
	// Vertical margins are collapsed in these cases:
	// 1) Adjacent siblings
	// 2) No content separating parent and descendants. The margin ends up outside the parent.
	// 3) Empty blocks

	layout_collapse_margin_with_self(ctx, box);
	layout_collapse_margin_with_children(ctx, box);
	layout_collapse_margin_with_siblings(ctx, box);
}

void
fz_restartable_layout_html(fz_context *ctx, fz_html_tree *tree, float start_x, float start_y, float page_w, float page_h, float em, fz_html_restarter *restart)
{
	int unlocked = 0;
	layout_data ld = { 0 };
	fz_html_box *box = tree->root;

	fz_var(ld.hb_buf);
	fz_var(unlocked);

	// nothing to layout
	if (!box->down)
	{
		fz_warn(ctx, "html: nothing to layout");
		box->s.layout.em = em;
		box->s.layout.baseline = 0;
		box->s.layout.x = start_x;
		box->s.layout.w = page_w;
		box->s.layout.y = start_y;
		box->s.layout.b = start_y;
		return;
	}

	fz_hb_lock(ctx);

	fz_try(ctx)
	{
		Memento_startLeaking(); /* HarfBuzz leaks harmlessly */
		ld.hb_buf = hb_buffer_create();
		Memento_stopLeaking(); /* HarfBuzz leaks harmlessly */
		unlocked = 1;
		fz_hb_unlock(ctx);

		ld.restart = restart;
		ld.page_h = page_h;
		ld.page_top = start_y;
		ld.pool = tree->pool;
		if (restart)
			restart->potential = NULL;

		// Update em/margin/padding/border if necessary.
		if (box->s.layout.em != em || box->s.layout.x != start_x || box->s.layout.w != page_w)
		{
			box->s.layout.em = em;
			box->s.layout.baseline = 0;
			box->s.layout.x = start_x;
			box->s.layout.w = page_w;
			layout_update_styles(ctx, box->down, box);
			layout_update_widths(ctx, box->down, box, ld.hb_buf);
			layout_collapse_margins(ctx, box->down, box);
		}

		box->s.layout.y = start_y;
		box->s.layout.b = start_y;

		assert(box->type == BOX_BLOCK);
		layout_block(ctx, &ld, box, box); // HACK: layout box with itself as parent!
	}
	fz_always(ctx)
	{
		if (unlocked)
			fz_hb_lock(ctx);
		hb_buffer_destroy(ld.hb_buf);
		fz_hb_unlock(ctx);
	}
	fz_catch(ctx)
	{
		fz_rethrow(ctx);
	}
}

void
fz_layout_html(fz_context *ctx, fz_html *html, float w, float h, float em)
{
	/* If we're already laid out to the specifications we need,
	 * nothing to do. */
	if (html->layout_w == w && html->layout_h == h && html->layout_em == em)
		return;

	html->page_margin[T] = fz_from_css_number(html->tree.root->style->margin[T], em, em, 0);
	html->page_margin[B] = fz_from_css_number(html->tree.root->style->margin[B], em, em, 0);
	html->page_margin[L] = fz_from_css_number(html->tree.root->style->margin[L], em, em, 0);
	html->page_margin[R] = fz_from_css_number(html->tree.root->style->margin[R], em, em, 0);

	html->page_w = w - html->page_margin[L] - html->page_margin[R];
	if (html->page_w <= 72)
		html->page_w = 72; /* enforce a minimum page size! */
	if (h > 0)
	{
		html->page_h = h - html->page_margin[T] - html->page_margin[B];
		if (html->page_h <= 72)
			html->page_h = 72; /* enforce a minimum page size! */
	}
	else
	{
		/* h 0 means no pagination */
		html->page_h = 0;
	}

	fz_restartable_layout_html(ctx, &html->tree, 0, 0, html->page_w, html->page_h, em, NULL);

	if (h == 0)
		html->page_h = html->tree.root->s.layout.b;

	/* Remember how we're laid out so we can avoid needless
	 * relayouts in future. */
	html->layout_w = w;
	html->layout_h = h;
	html->layout_em = em;

#ifndef NDEBUG
	if (fz_atoi(getenv("FZ_DEBUG_HTML")))
		fz_debug_html(ctx, html->tree.root);
#endif
}

/* === DRAW === */

typedef struct
{
	float rgb[3];
	float a;
} unpacked_color;

static inline unpacked_color
unpack_color(const fz_css_color src)
{
	unpacked_color dst;
	dst.rgb[0] = src.r / 255.0f;
	dst.rgb[1] = src.g / 255.0f;
	dst.rgb[2] = src.b / 255.0f;
	dst.a = src.a / 255.0f;
	return dst;
}

static inline int
color_eq(fz_css_color a, fz_css_color b)
{
	return a.r == b.r && a.g == b.g && a.b == b.b && a.a == b.a;
}

static int draw_flow_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_device *dev, fz_matrix ctm, hb_buffer_t *hb_buf, fz_html_restarter *restart)
{
	fz_html_flow *node;
	fz_text *text = NULL;
	fz_path *line = NULL;
	fz_matrix trm;
	fz_css_color prev_color = { 0, 0, 0, 0 };
	fz_css_color prev_fill_color = { 0, 0, 0, 0 };
	fz_css_color prev_stroke_color = { 0, 0, 0, 0 };
	float line_width, prev_line_width = 0;
	int filling, prev_filling = 0;
	int stroking, prev_stroking = 0;
	int restartable_ended = 0;
	fz_stroke_state *ss = NULL;
	fz_stroke_state *line_ss = NULL;

	fz_var(text);
	fz_var(line);
	fz_var(ss);
	fz_var(line_ss);

	/* FIXME: HB_DIRECTION_TTB? */

	if (restart && restart->start != NULL && restart->start != box)
		return 0;

	fz_try(ctx)
	{
		for (node = box->u.flow.head; node; node = node->next)
		{
			const fz_css_style *style = node->box->style;

			if (restart)
			{
				if (restart->start_flow != NULL)
				{
					if (restart->start_flow != node)
						continue;
					restart->start = NULL;
					restart->start_flow = NULL;
				}

				if (restart->end == box && restart->end_flow == node)
				{
					restartable_ended = 1;
					break;
				}
			}

			if (node->type == FLOW_IMAGE)
			{
				if (node->y >= page_bot || node->y + node->h <= page_top)
					continue;
			}
			else
			{
				if (node->y > page_bot || node->y < page_top)
					continue;
			}

			if (node->type == FLOW_WORD || node->type == FLOW_SPACE || node->type == FLOW_SHYPHEN)
			{
				string_walker walker;
				const char *s;
				float x, y;
				float em;

				if (node->type == FLOW_SPACE && node->breaks_line)
					continue;
				if (node->type == FLOW_SHYPHEN && !node->breaks_line)
					continue;
				if (style->visibility != V_VISIBLE)
					continue;

				em = node->box->s.layout.em;

				line_width = fz_from_css_number(style->text_stroke_width, em, em, 0);
				filling = style->text_fill_color.a != 0;
				stroking = style->text_stroke_color.a != 0;
				if (stroking)
				{
					if (ss == NULL)
						ss = fz_new_stroke_state(ctx);
				}
				if (line)
				{
					if (line_ss == NULL)
						line_ss = fz_new_stroke_state(ctx);
				}

				if (	/* If we've changed whether we're filling... */
					filling != prev_filling ||
					/* Or we're filling and the color has changed... */
					(prev_filling && !color_eq(style->text_fill_color, prev_fill_color)) ||
					/* Or we've changed whether we're stroking... */
					stroking != prev_stroking ||
					/* Or we're stroking, and the color or linewidth has changed... */
					(prev_stroking && (!color_eq(style->text_stroke_color, prev_stroke_color) || line_width != prev_line_width)))
				{
					if (text)
					{
						if (prev_filling)
						{
							unpacked_color color = unpack_color(prev_fill_color);
							fz_fill_text(ctx, dev, text, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
						}
						if (prev_stroking)
						{
							unpacked_color color = unpack_color(prev_stroke_color);
							ss->linewidth = prev_line_width;
							fz_stroke_text(ctx, dev, text, ss, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
						}
						fz_drop_text(ctx, text);
						text = NULL;
					}
					prev_filling = filling;
					prev_stroking = stroking;
				}
				prev_fill_color = style->text_fill_color;
				prev_stroke_color = style->text_stroke_color;
				prev_line_width = line_width;

				if (!color_eq(style->color, prev_color))
				{
					if (line)
					{
						unpacked_color color = unpack_color(prev_color);
						fz_stroke_path(ctx, dev, line, line_ss, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
						fz_drop_path(ctx, line);
						line = NULL;
					}
					prev_color = style->color;
				}

				if (style->text_decoration > 0)
				{
					if (!line)
					{
						line = fz_new_path(ctx);
						if (line_ss == NULL)
							line_ss = fz_new_stroke_state(ctx);
					}
					if (style->text_decoration & TD_UNDERLINE)
					{
						fz_moveto(ctx, line, node->x, node->y + 1.5f - page_top);
						fz_lineto(ctx, line, node->x + node->w, node->y + 1.5f - page_top);
					}
					if (style->text_decoration & TD_LINE_THROUGH)
					{
						fz_moveto(ctx, line, node->x, node->y - em * 0.3f - page_top);
						fz_lineto(ctx, line, node->x + node->w, node->y - em * 0.3f - page_top);
					}
				}

				if (!text)
					text = fz_new_text(ctx);

				if (node->bidi_level & 1)
					x = node->x + node->w;
				else
					x = node->x;
				y = node->y;

				trm.a = em;
				trm.b = 0;
				trm.c = 0;
				trm.d = -em;
				trm.e = x;
				trm.f = y - page_top;

				s = get_node_text(ctx, node);
				init_string_walker(ctx, &walker, hb_buf, node->bidi_level & 1, style->font, node->script, node->markup_lang, style->small_caps, s);
				while (walk_string(&walker))
				{
					float node_scale = node->box->s.layout.em / walker.scale;
					unsigned int i;
					uint32_t k;
					int c, n;

					/* Flatten advance and offset into offset array. */
					int x_advance = 0;
					int y_advance = 0;
					for (i = 0; i < walker.glyph_count; ++i)
					{
						walker.glyph_pos[i].x_offset += x_advance;
						walker.glyph_pos[i].y_offset += y_advance;
						x_advance += walker.glyph_pos[i].x_advance;
						y_advance += walker.glyph_pos[i].y_advance;
					}

					if (node->bidi_level & 1)
						x -= x_advance * node_scale;

					/* Walk characters to find glyph clusters */
					k = 0;
					while (walker.start + k < walker.end)
					{
						n = fz_chartorune(&c, walker.start + k);

						for (i = 0; i < walker.glyph_count; ++i)
						{
							if (walker.glyph_info[i].cluster == k)
							{
								trm.e = x + walker.glyph_pos[i].x_offset * node_scale;
								trm.f = y - walker.glyph_pos[i].y_offset * node_scale - page_top;
								fz_show_glyph(ctx, text, walker.font, trm,
										walker.glyph_info[i].codepoint, c,
										0, node->bidi_level, box->markup_dir, node->markup_lang);
								c = -1; /* for subsequent glyphs in x-to-many mappings */
							}
						}

						/* no glyph found (many-to-many or many-to-one mapping) */
						if (c != -1)
						{
							fz_show_glyph(ctx, text, walker.font, trm,
									-1, c,
									0, node->bidi_level, box->markup_dir, node->markup_lang);
						}

						k += n;
					}

					if ((node->bidi_level & 1) == 0)
						x += x_advance * node_scale;

					y += y_advance * node_scale;
				}
			}
			else if (node->type == FLOW_IMAGE)
			{
				if (text)
				{
					if (filling)
					{
						unpacked_color color = unpack_color(prev_fill_color);
						fz_fill_text(ctx, dev, text, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
					}
					if (stroking)
					{
						unpacked_color color = unpack_color(prev_stroke_color);
						ss->linewidth = line_width;
						fz_stroke_text(ctx, dev, text, ss, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
					}
					fz_drop_text(ctx, text);
					text = NULL;
				}
				if (style->visibility == V_VISIBLE)
				{
					float alpha = style->color.a / 255.0f;
					fz_matrix itm = fz_pre_translate(ctm, node->x, node->y - page_top);
					itm = fz_pre_scale(itm, node->w, node->h);
					fz_fill_image(ctx, dev, node->content.image, itm, alpha, fz_default_color_params);
				}
			}
		}

		if (text)
		{
			if (filling)
			{
				unpacked_color color = unpack_color(prev_fill_color);
				fz_fill_text(ctx, dev, text, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
			}
			if (stroking)
			{
				unpacked_color color = unpack_color(prev_stroke_color);
				ss->linewidth = prev_line_width;
				fz_stroke_text(ctx, dev, text, ss, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
			}
			fz_drop_text(ctx, text);
			text = NULL;
		}

		if (line)
		{
			unpacked_color color = unpack_color(prev_color);
			fz_stroke_path(ctx, dev, line, line_ss, ctm, fz_device_rgb(ctx), color.rgb, color.a, fz_default_color_params);
			fz_drop_path(ctx, line);
			line = NULL;
		}
	}
	fz_always(ctx)
	{
		fz_drop_text(ctx, text);
		fz_drop_path(ctx, line);
		fz_drop_stroke_state(ctx, ss);
		fz_drop_stroke_state(ctx, line_ss);
	}
	fz_catch(ctx)
		fz_rethrow(ctx);

	return restartable_ended;
}

static void draw_rect(fz_context *ctx, fz_device *dev, fz_matrix ctm, float page_top, fz_css_color color, float x0, float y0, float x1, float y1)
{
	if (color.a > 0)
	{
		float rgb[3];

		fz_path *path = fz_new_path(ctx);

		fz_moveto(ctx, path, x0, y0 - page_top);
		fz_lineto(ctx, path, x1, y0 - page_top);
		fz_lineto(ctx, path, x1, y1 - page_top);
		fz_lineto(ctx, path, x0, y1 - page_top);
		fz_closepath(ctx, path);

		rgb[0] = color.r / 255.0f;
		rgb[1] = color.g / 255.0f;
		rgb[2] = color.b / 255.0f;

		fz_fill_path(ctx, dev, path, 0, ctm, fz_device_rgb(ctx), rgb, color.a / 255.0f, fz_default_color_params);

		fz_drop_path(ctx, path);
	}
}

static const char *roman_uc[3][10] = {
	{ "", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX" },
	{ "", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC" },
	{ "", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM" },
};

static const char *roman_lc[3][10] = {
	{ "", "i", "ii", "iii", "iv", "v", "vi", "vii", "viii", "ix" },
	{ "", "x", "xx", "xxx", "xl", "l", "lx", "lxx", "lxxx", "xc" },
	{ "", "c", "cc", "ccc", "cd", "d", "dc", "dcc", "dccc", "cm" },
};

static void format_roman_number(fz_context *ctx, char *buf, int size, int n, const char *sym[3][10], const char *sym_m)
{
	int I = n % 10;
	int X = (n / 10) % 10;
	int C = (n / 100) % 10;
	int M = (n / 1000);

	fz_strlcpy(buf, "", size);
	while (M--)
		fz_strlcat(buf, sym_m, size);
	fz_strlcat(buf, sym[2][C], size);
	fz_strlcat(buf, sym[1][X], size);
	fz_strlcat(buf, sym[0][I], size);
	fz_strlcat(buf, ". ", size);
}

static void format_alpha_number(fz_context *ctx, char *buf, int size, int n, int alpha, int omega)
{
	int base = omega - alpha + 1;
	int tmp[40];
	int i, c;

	if (alpha > 256) /* to skip final-s for greek */
		--base;

	/* Bijective base-26 (base-24 for greek) numeration */
	i = 0;
	while (n > 0)
	{
		--n;
		c = n % base + alpha;
		if (alpha > 256 && c > alpha + 16) /* skip final-s for greek */
			++c;
		tmp[i++] = c;
		n /= base;
	}

	while (i > 0)
		buf += fz_runetochar(buf, tmp[--i]);
	*buf++ = '.';
	*buf++ = ' ';
	*buf = 0;
}

static void format_list_number(fz_context *ctx, int type, int x, char *buf, int size)
{
	switch (type)
	{
	case LST_NONE: fz_strlcpy(buf, "", size); break;
	case LST_DISC: fz_snprintf(buf, size, "%C  ", 0x2022); break; /* U+2022 BULLET */
	case LST_CIRCLE: fz_snprintf(buf, size, "%C  ", 0x25CB); break; /* U+25CB WHITE CIRCLE */
	case LST_SQUARE: fz_snprintf(buf, size, "%C  ", 0x25A0); break; /* U+25A0 BLACK SQUARE */
	default:
	case LST_DECIMAL: fz_snprintf(buf, size, "%d. ", x); break;
	case LST_DECIMAL_ZERO: fz_snprintf(buf, size, "%02d. ", x); break;
	case LST_LC_ROMAN: format_roman_number(ctx, buf, size, x, roman_lc, "m"); break;
	case LST_UC_ROMAN: format_roman_number(ctx, buf, size, x, roman_uc, "M"); break;
	case LST_LC_ALPHA: format_alpha_number(ctx, buf, size, x, 'a', 'z'); break;
	case LST_UC_ALPHA: format_alpha_number(ctx, buf, size, x, 'A', 'Z'); break;
	case LST_LC_LATIN: format_alpha_number(ctx, buf, size, x, 'a', 'z'); break;
	case LST_UC_LATIN: format_alpha_number(ctx, buf, size, x, 'A', 'Z'); break;
	case LST_LC_GREEK: format_alpha_number(ctx, buf, size, x, 0x03B1, 0x03C9); break;
	case LST_UC_GREEK: format_alpha_number(ctx, buf, size, x, 0x0391, 0x03A9); break;
	}
}

static fz_html_flow *find_list_mark_anchor(fz_context *ctx, fz_html_box *box)
{
	/* find first flow node in <li> tag */
	while (box)
	{
		if (box->type == BOX_FLOW)
			return box->u.flow.head;
		box = box->down;
	}
	return NULL;
}

static void draw_list_mark(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_device *dev, fz_matrix ctm, int n)
{
	fz_font *font;
	fz_text *text;
	fz_matrix trm;
	fz_html_flow *line;
	float y, w;
	float color[4];
	const char *s;
	char buf[40];
	int c, g;

	trm = fz_scale(box->s.layout.em, -box->s.layout.em);

	line = find_list_mark_anchor(ctx, box);
	if (line)
	{
		y = line->y;
	}
	else
	{
		float h = fz_from_css_number_scale(box->style->line_height, box->s.layout.em);
		float a = box->s.layout.em * 0.8f;
		float d = box->s.layout.em * 0.2f;
		if (a + d > h)
			h = a + d;
		y = box->s.layout.y + a + (h - a - d) / 2;
	}

	if (y > page_bot || y < page_top)
		return;

	format_list_number(ctx, box->style->list_style_type, n, buf, sizeof buf);

	s = buf;
	w = 0;
	while (*s)
	{
		s += fz_chartorune(&c, s);
		g = fz_encode_character_with_fallback(ctx, box->style->font, c, UCDN_SCRIPT_LATIN, FZ_LANG_UNSET, &font);
		w += fz_advance_glyph(ctx, font, g, 0) * box->s.layout.em;
	}

	text = fz_new_text(ctx);

	fz_try(ctx)
	{
		s = buf;
		trm.e = box->s.layout.x - w;
		trm.f = y - page_top;
		while (*s)
		{
			s += fz_chartorune(&c, s);
			g = fz_encode_character_with_fallback(ctx, box->style->font, c, UCDN_SCRIPT_LATIN, FZ_LANG_UNSET, &font);
			fz_show_glyph(ctx, text, font, trm, g, c, 0, 0, FZ_BIDI_NEUTRAL, FZ_LANG_UNSET);
			trm.e += fz_advance_glyph(ctx, font, g, 0) * box->s.layout.em;
		}

		color[0] = box->style->color.r / 255.0f;
		color[1] = box->style->color.g / 255.0f;
		color[2] = box->style->color.b / 255.0f;
		color[3] = box->style->color.a / 255.0f;

		fz_fill_text(ctx, dev, text, ctm, fz_device_rgb(ctx), color, color[3], fz_default_color_params);
	}
	fz_always(ctx)
		fz_drop_text(ctx, text);
	fz_catch(ctx)
		fz_rethrow(ctx);
}

static int draw_block_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_device *dev, fz_matrix ctm, hb_buffer_t *hb_buf, fz_html_restarter *restart);
static int draw_table_row(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_device *dev, fz_matrix ctm, hb_buffer_t *hb_buf, fz_html_restarter *restart);

static int draw_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_device *dev, fz_matrix ctm, hb_buffer_t *hb_buf, fz_html_restarter *restart)
{
	int ret = 0;
	int str = fz_html_tag_to_structure(box->tag);

	if (str != FZ_STRUCTURE_INVALID)
		fz_begin_structure(ctx, dev, str, box->tag, 0);

	switch (box->type)
	{
	case BOX_TABLE_ROW:
		if (restart && restart->end == box)
			ret = 1;
		else if (draw_table_row(ctx, box, page_top, page_bot, dev, ctm, hb_buf, restart))
			ret = 1;
		break;
	case BOX_TABLE:
	case BOX_TABLE_CELL:
	case BOX_BLOCK:
		if (restart && restart->end == box)
			ret = 1;
		else if (draw_block_box(ctx, box, page_top, page_bot, dev, ctm, hb_buf, restart))
			ret = 1;
		break;
	case BOX_FLOW:
		if (draw_flow_box(ctx, box, page_top, page_bot, dev, ctm, hb_buf, restart))
			ret = 1;
		break;
	}

	if (str != FZ_STRUCTURE_INVALID)
		fz_end_structure(ctx, dev);

	return ret;
}

static void
do_borders(fz_context *ctx, fz_device *dev, fz_matrix ctm, float page_top, fz_html_box *box, int suppress)
{
	float *border = box->u.block.border;
	float *padding = box->u.block.padding;
	float x0 = box->s.layout.x - padding[L];
	float y0 = box->s.layout.y - padding[T];
	float x1 = box->s.layout.x + box->s.layout.w + padding[R];
	float y1 = box->s.layout.b + padding[B];

	if (border[T] > 0 && !(suppress & (1<<T)))
		draw_rect(ctx, dev, ctm, page_top, box->style->border_color[T], x0 - border[L], y0 - border[T], x1 + border[R], y0);
	if (border[R] > 0 && !(suppress & (1<<R)))
		draw_rect(ctx, dev, ctm, page_top, box->style->border_color[R], x1, y0 - border[T], x1 + border[R], y1 + border[B]);
	if (border[B] > 0 && !(suppress & (1<<B)))
		draw_rect(ctx, dev, ctm, page_top, box->style->border_color[B], x0 - border[L], y1, x1 + border[R], y1 + border[B]);
	if (border[L] > 0 && !(suppress & (1<<L)))
		draw_rect(ctx, dev, ctm, page_top, box->style->border_color[L], x0 - border[L], y0 - border[T], x0, y1 + border[B]);
}

static int draw_block_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_device *dev, fz_matrix ctm, hb_buffer_t *hb_buf, fz_html_restarter *restart)
{
	fz_html_box *child;
	float x0, y0, x1, y1;

	float *padding = box->u.block.padding;
	int stopped = 0;
	int skipping;

	assert(fz_html_box_has_boxes(box));
	x0 = box->s.layout.x - padding[L];
	y0 = box->s.layout.y - padding[T];
	x1 = box->s.layout.x + box->s.layout.w + padding[R];
	y1 = box->s.layout.b + padding[B];

	if (y0 > page_bot || y1 < page_top)
		return 0;

	/* If we're skipping, is this the place we should restart? */
	if (restart)
	{
		if (restart->start == box)
			restart->start = NULL;
		if (restart->end == box)
			return 1;
	}

	if (restart && restart->end == box)
		return 1;

	/* Are we skipping? */
	skipping = (restart && restart->start != NULL);

	/* Only draw the content if it's visible */
	if (box->style->visibility == V_VISIBLE)
	{
		int suppress;

		/* We draw the background rectangle regardless if we are skipping or not, because
		 * we might find the end-of-skip point inside this box. If there is no content
		 * then the box height will be 0, so nothing will be drawn. */
		if (y1 > y0)
			draw_rect(ctx, dev, ctm, page_top, box->style->background_color, x0, y0, x1, y1);

		if (!skipping)
		{
			/* Draw a selection of borders. */
			/* If we are restarting, don't do the bottom one yet. */
			suppress = restart ? (1<<B) : 0;
			do_borders(ctx, dev, ctm, page_top, box, suppress);

			if (box->list_item)
				draw_list_mark(ctx, box, page_top, page_bot, dev, ctm, box->list_item);
		}
	}

	for (child = box->down; child; child = child->next)
	{
		if (draw_box(ctx, child, page_top, page_bot, dev, ctm, hb_buf, restart))
		{
			stopped = 1;
			break;
		}
	}

	if (box->style->visibility == V_VISIBLE && restart && restart->start == NULL)
	{
		/* We didn't draw (at least some of) the borders on the way down,
		 * because we were in restart mode. */

		/* We never want to draw the top one. Either it will have been drawn
		 * before, or we were skipping at that point. */
		int suppress = (1<<T);

		/* If we were skipping, and we're not any more, better draw in the
		 * left and right ones we missed. */
		suppress += (skipping && restart->start == NULL) ? 0 : ((1<<L) + (1<<R));

		/* If we've stopped now, don't do the bottom one either. */
		suppress += stopped ? (1<<B) : 0;

		/* FIXME: background color? list mark is probably OK as we only want
		 * it once. */

		do_borders(ctx, dev, ctm, page_top, box, suppress);
	}

	return stopped;
}

static int draw_table_row(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_device *dev, fz_matrix ctm, hb_buffer_t *hb_buf, fz_html_restarter *restart)
{
	/* Table rows don't draw background colors or borders */

	fz_html_box *child;

	float y0 = box->s.layout.y;
	float y1 = box->s.layout.b;
	if (y0 > page_bot || y1 < page_top)
		return 0;

	/* If we're skipping, is this the place we should restart? */
	if (restart)
	{
		if (restart->start == box)
			restart->start = NULL;
		if (restart->end == box)
			return 1;
	}

	if (restart && restart->end == box)
		return 1;

	for (child = box->down; child; child = child->next)
		if (draw_box(ctx, child, page_top, page_bot, dev, ctm, hb_buf, restart))
			return 1;

	return 0;
}

void
fz_draw_restarted_html(fz_context *ctx, fz_device *dev, fz_matrix ctm, fz_html_box *top, float page_top, float page_bot, fz_html_restarter *restart)
{
	fz_html_box *box;
	hb_buffer_t *hb_buf = NULL;
	int unlocked = 0;

	fz_var(hb_buf);
	fz_var(unlocked);

	fz_hb_lock(ctx);
	fz_try(ctx)
	{
		hb_buf = hb_buffer_create();
		fz_hb_unlock(ctx);
		unlocked = 1;

		for (box = top->down; box; box = box->next)
			if (draw_box(ctx, box, page_top, page_bot, dev, ctm, hb_buf, restart))
				break;
	}
	fz_always(ctx)
	{
		if (unlocked)
			fz_hb_lock(ctx);
		hb_buffer_destroy(hb_buf);
		fz_hb_unlock(ctx);
	}
	fz_catch(ctx)
	{
		fz_rethrow(ctx);
	}
}

void
fz_draw_html(fz_context *ctx, fz_device *dev, fz_matrix ctm, fz_html *html, int page)
{
	float page_top = page * html->page_h;
	float page_bot = (page + 1) * html->page_h;

	draw_rect(ctx, dev, ctm, 0, html->tree.root->style->background_color,
			0, 0,
			html->page_w + html->page_margin[L] + html->page_margin[R],
			html->page_h + html->page_margin[T] + html->page_margin[B]);

	ctm = fz_pre_translate(ctm, html->page_margin[L], html->page_margin[T]);

	fz_draw_restarted_html(ctx, dev, ctm, html->tree.root, page_top, page_bot, NULL);
}

void fz_draw_story(fz_context *ctx, fz_story *story, fz_device *dev, fz_matrix ctm)
{
	float page_top, page_bot;
	fz_html_box *b;
	fz_path *clip;
	fz_rect bbox;

	if (story == NULL || story->complete)
		return;

	bbox = story->bbox;
	b = story->tree.root;
	page_top = b->s.layout.y - b->u.block.margin[T] - b->u.block.border[T] - b->u.block.padding[T];
	page_bot = b->s.layout.b + b->u.block.margin[B] + b->u.block.border[B] + b->u.block.padding[B];

	if (dev)
	{
		clip = fz_new_path(ctx);
		fz_try(ctx)
		{
			fz_moveto(ctx, clip, bbox.x0, bbox.y0);
			fz_lineto(ctx, clip, bbox.x1, bbox.y0);
			fz_lineto(ctx, clip, bbox.x1, bbox.y1);
			fz_lineto(ctx, clip, bbox.x0, bbox.y1);
			fz_closepath(ctx, clip);
			fz_clip_path(ctx, dev, clip, 0, ctm, bbox);
		}
		fz_always(ctx)
			fz_drop_path(ctx, clip);
		fz_catch(ctx)
			fz_rethrow(ctx);
	}

	story->restart_place = story->restart_draw;
	if (dev)
		fz_draw_restarted_html(ctx, dev, ctm, story->tree.root->down, 0, page_bot+page_top, &story->restart_place);
	story->restart_place.start = story->restart_draw.end;
	story->restart_place.start_flow = story->restart_draw.end_flow;
	story->restart_place.end = NULL;
	story->restart_place.end_flow = NULL;
	story->rect_count++;

	if (story->restart_place.start == NULL)
		story->complete = 1;

	if (dev)
		fz_pop_clip(ctx, dev);
}

void fz_reset_story(fz_context *ctx, fz_story *story)
{
	if (story == NULL)
		return;

	story->restart_place.start = NULL;
	story->restart_place.start_flow = NULL;
	story->restart_place.end = NULL;
	story->restart_place.end_flow = NULL;
	story->restart_draw.start = NULL;
	story->restart_draw.start_flow = NULL;
	story->restart_draw.end = NULL;
	story->restart_draw.end_flow = NULL;
	story->rect_count = 0;
	story->complete = 0;
}

static char *
gather_text(fz_context *ctx, fz_html_box *box)
{
	fz_html_flow *node;
	char *text = NULL;

	fz_var(text);

	fz_try(ctx)
	{
		for (node = box->u.flow.head; node; node = node->next)
		{
			const fz_css_style *style = node->box->style;

			if (node->type == FLOW_WORD || node->type == FLOW_SPACE || node->type == FLOW_SHYPHEN)
			{
				const char *s;

				if (node->type == FLOW_SPACE && node->breaks_line)
					continue;
				if (node->type == FLOW_SHYPHEN && !node->breaks_line)
					continue;
				if (style->visibility != V_VISIBLE)
					continue;

				s = get_node_text(ctx, node);

				if (text)
				{
					size_t newsize = strlen(text) + strlen(s) + 1;
					text = fz_realloc(ctx, text, newsize);
					strcat(text, s);
				}
				else
				{
					text = fz_strdup(ctx, s);
				}
			}
			else if (node->type == FLOW_IMAGE)
			{
			}
		}

	}
	fz_catch(ctx)
	{
		fz_free(ctx, text);
		fz_rethrow(ctx);
	}

	return text;
}

static int enumerate_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_story_position_callback *cb, void *arg, int depth, int rect_num, fz_html_restarter *restart);

static int enumerate_block_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_story_position_callback *cb, void *arg, int depth, int rect_num, fz_html_restarter *restart)
{
	fz_html_box *child;
	float y0, y1;

	float *padding = box->u.block.padding;
	int stopped = 0;
	int skipping;
	fz_story_element_position pos;
	int heading;

	assert(fz_html_box_has_boxes(box));
	y0 = box->s.layout.y - padding[T];
	y1 = box->s.layout.b + padding[B];

	if (y0 > page_bot || y1 < page_top)
		return 0;

	/* If we're skipping, is this the place we should restart? */
	if (restart)
	{
		if (restart->start == box)
			restart->start = NULL;
		if (restart->end == box)
			return 1;
	}

	if (restart && restart->end == box)
		return 1;

	/* Are we skipping? */
	skipping = (restart && restart->start != NULL);

	if (box->style->visibility == V_VISIBLE && !skipping)
	{
		heading = box->heading;
		if (heading || box->id != NULL || box->href)
		{
			/* We have a box worthy of a callback. */
			char *text = NULL;
			pos.text = NULL;
			if (heading && box->down)
				pos.text = text = gather_text(ctx, box->down);
			pos.depth = depth;
			pos.heading = heading;
			pos.open_close = 1;
			pos.id = box->id;
			pos.href = box->href;
			pos.rect.x0 = box->s.layout.x;
			pos.rect.y0 = box->s.layout.y;
			pos.rect.x1 = box->s.layout.x + box->s.layout.w;
			pos.rect.y1 = box->s.layout.b;
			pos.rectangle_num = rect_num;
			fz_try(ctx)
				cb(ctx, arg, &pos);
			fz_always(ctx)
				fz_free(ctx, text);
			fz_catch(ctx)
				fz_rethrow(ctx);
			pos.text = NULL;
		}
	}

	for (child = box->down; child; child = child->next)
	{
		if (enumerate_box(ctx, child, page_top, page_bot, cb, arg, depth+1, rect_num, restart))
		{
			stopped = 1;
			break;
		}
	}

	if (box->style->visibility == V_VISIBLE && !skipping)
	{
		if (heading || box->id != NULL || box->href)
		{
			/* We have a box worthy of a callback that needs closing. */
			pos.open_close = 2;
			pos.rectangle_num = rect_num;
			cb(ctx, arg, &pos);
		}
	}

	return stopped;
}

static int enumerate_flow_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_story_position_callback *cb, void *arg, int depth, int rect_num, fz_html_restarter *restart)
{
	fz_html_flow *node;
	int restartable_ended = 0;

	/* FIXME: HB_DIRECTION_TTB? */

	if (restart && restart->start != NULL && restart->start != box)
		return 0;

	for (node = box->u.flow.head; node; node = node->next)
	{
		const fz_css_style *style = node->box->style;

		if (restart)
		{
			if (restart->start_flow != NULL)
			{
				if (restart->start_flow != node)
					continue;
				restart->start = NULL;
				restart->start_flow = NULL;
			}

			if (restart->end == box && restart->end_flow == node)
			{
				restartable_ended = 1;
				break;
			}
		}

		if (node->type == FLOW_IMAGE)
		{
			if (node->y >= page_bot || node->y + node->h <= page_top)
				continue;
		}
		else
		{
			if (node->y > page_bot || node->y < page_top)
				continue;
		}

		if (node->box->id || node->box->href)
		{
			/* We have a node to callback for. */
			fz_story_element_position pos;

			pos.text = NULL;
			pos.depth = depth;
			pos.heading = 0;
			pos.open_close = 1 | 2;
			pos.id = node->box->id;
			pos.href = node->box->href;
			/* We only have the baseline and the em, so the bbox is a bit of a fudge. */
			pos.rect.x0 = node->x;
			pos.rect.y0 = node->y - node->h * 0.8f;
			pos.rect.x1 = node->x + node->w;
			pos.rect.y1 = node->y + node->h * 0.2f;
			pos.rectangle_num = rect_num;
			cb(ctx, arg, &pos);
		}

		if (node->type == FLOW_WORD || node->type == FLOW_SPACE || node->type == FLOW_SHYPHEN)
		{
		}
		else if (node->type == FLOW_IMAGE)
		{
			if (style->visibility == V_VISIBLE)
			{
				/* FIXME: Maybe callback for images? */
			}
		}
	}

	return restartable_ended;
}

static int enumerate_box(fz_context *ctx, fz_html_box *box, float page_top, float page_bot, fz_story_position_callback *cb, void *arg, int depth, int rect_num, fz_html_restarter *restart)
{
	switch (box->type)
	{
	case BOX_TABLE:
	case BOX_TABLE_ROW:
	case BOX_TABLE_CELL:
	case BOX_BLOCK:
		if (restart && restart->end == box)
			return 1;
		if (enumerate_block_box(ctx, box, page_top, page_bot, cb, arg, depth, rect_num, restart))
			return 1;
		break;
	case BOX_FLOW:
		if (enumerate_flow_box(ctx, box, page_top, page_bot, cb, arg, depth, rect_num, restart))
			return 1;
		break;
	}

	return 0;
}

void fz_story_positions(fz_context *ctx, fz_story *story, fz_story_position_callback *cb, void *arg)
{
	float page_top, page_bot;
	fz_html_box *b;
	fz_html_restarter restart;
	fz_html_box *box;
	fz_html_box *top;

	if (story == NULL || story->complete)
		return;

	b = story->tree.root;
	page_top = b->s.layout.y - b->u.block.margin[T] - b->u.block.border[T] - b->u.block.padding[T];
	page_bot = b->s.layout.b + b->u.block.margin[B] + b->u.block.border[B] + b->u.block.padding[B];
	top = story->tree.root->down;

	restart = story->restart_draw;

	for (box = top->down; box; box = box->next)
		if (enumerate_box(ctx, box, page_top, page_bot, cb, arg, 0, story->rect_count+1, &restart))
			break;
}