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LibWeb: Iterate over text chunks using a grapheme-aware segmenter

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Our current text iterator is not aware of multi-code point graphemes.
Instead of simply incrementing an iterator one code point at a time, use
our Unicode grapheme segmenter to break text into fragments.
This commit is contained in:
Timothy Flynn 2024-09-20 17:14:14 -04:00 committed by Andreas Kling
parent aef85a83bd
commit f0105b473b
Notes: github-actions[bot] 2024-09-21 06:58:43 +00:00 
Author: https://github.com/trflynn89
Commit: https://github.com/LadybirdBrowser/ladybird/commit/f0105b473b9
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1465
5 changed files with 84 additions and 32 deletions
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34
Tests/LibWeb/Layout/expected/multi-code-point-graphemes.txt Normal file
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@ -0,0 +1,34 @@
Viewport <#document> at (0,0) content-size 800x600 children: not-inline
BlockContainer <html> at (0,0) content-size 800x600 [BFC] children: not-inline
BlockContainer <body> at (8,16) content-size 784x83 children: not-inline
BlockContainer <p> at (8,16) content-size 784x17 children: inline
frag 0 from TextNode start: 0, length: 11, rect: [8,16 20.3125x17] baseline: 13.296875
"🧑‍🚒"
TextNode <#text>
BlockContainer <(anonymous)> at (8,49) content-size 784x0 children: inline
TextNode <#text>
BlockContainer <p> at (8,49) content-size 784x17 children: inline
frag 0 from TextNode start: 0, length: 13, rect: [8,49 20.3125x17] baseline: 13.296875
"🏴‍☠️"
TextNode <#text>
BlockContainer <(anonymous)> at (8,82) content-size 784x0 children: inline
TextNode <#text>
BlockContainer <p> at (8,82) content-size 784x17 children: inline
frag 0 from TextNode start: 0, length: 25, rect: [8,82 20.3125x17] baseline: 13.296875
"🧑‍🧑‍🧒‍🧒"
TextNode <#text>
BlockContainer <(anonymous)> at (8,115) content-size 784x0 children: inline
TextNode <#text>
ViewportPaintable (Viewport<#document>) [0,0 800x600]
PaintableWithLines (BlockContainer<HTML>) [0,0 800x600]
PaintableWithLines (BlockContainer<BODY>) [8,16 784x83] overflow: [8,16 784x99]
PaintableWithLines (BlockContainer<P>) [8,16 784x17]
TextPaintable (TextNode<#text>)
PaintableWithLines (BlockContainer(anonymous)) [8,49 784x0]
PaintableWithLines (BlockContainer<P>) [8,49 784x17]
TextPaintable (TextNode<#text>)
PaintableWithLines (BlockContainer(anonymous)) [8,82 784x0]
PaintableWithLines (BlockContainer<P>) [8,82 784x17]
TextPaintable (TextNode<#text>)
PaintableWithLines (BlockContainer(anonymous)) [8,115 784x0]

3
Tests/LibWeb/Layout/input/multi-code-point-graphemes.html Normal file
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@ -0,0 +1,3 @@
<p>🧑‍🚒</p>
<p>🏴‍☠️</p>
<p>🧑‍🧑‍🧒‍🧒</p>

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Tests/LibWeb/Screenshot/images/text-direction-ref.png
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69
Userland/Libraries/LibWeb/Layout/TextNode.cpp
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@ -391,13 +391,14 @@ void TextNode::compute_text_for_rendering()
m_text_for_rendering = MUST(builder.to_string()); m_text_for_rendering = MUST(builder.to_string());
} }
TextNode::ChunkIterator::ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const& font_cascade_list) TextNode::ChunkIterator::ChunkIterator(String const& text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const& font_cascade_list)
: m_wrap_lines(wrap_lines) : m_wrap_lines(wrap_lines)
, m_respect_linebreaks(respect_linebreaks) , m_respect_linebreaks(respect_linebreaks)
, m_utf8_view(text) , m_utf8_view(text)
, m_iterator(m_utf8_view.begin())
, m_font_cascade_list(font_cascade_list) , m_font_cascade_list(font_cascade_list)
, m_segmenter(Unicode::Segmenter::create(Unicode::SegmenterGranularity::Grapheme))
{ {
m_segmenter->set_segmented_text(text);
} }
static Gfx::GlyphRun::TextType text_type_for_code_point(u32 code_point) static Gfx::GlyphRun::TextType text_type_for_code_point(u32 code_point)
@ -462,75 +463,85 @@ Optional<TextNode::Chunk> TextNode::ChunkIterator::peek(size_t count)
Optional<TextNode::Chunk> TextNode::ChunkIterator::next_without_peek() Optional<TextNode::Chunk> TextNode::ChunkIterator::next_without_peek()
{ {
if (m_iterator == m_utf8_view.end()) if (m_current_index >= m_utf8_view.byte_length())
return {}; return {};
auto start_of_chunk = m_iterator; auto current_code_point = [this]() {
return *m_utf8_view.iterator_at_byte_offset_without_validation(m_current_index);
};
auto next_grapheme_boundary = [this]() {
return m_segmenter->next_boundary(m_current_index).value_or(m_utf8_view.byte_length());
};
Gfx::Font const& font = m_font_cascade_list.font_for_code_point(*m_iterator); auto code_point = current_code_point();
auto text_type = text_type_for_code_point(*m_iterator); auto start_of_chunk = m_current_index;
while (m_iterator != m_utf8_view.end()) {
if (&font != &m_font_cascade_list.font_for_code_point(*m_iterator)) { Gfx::Font const& font = m_font_cascade_list.font_for_code_point(code_point);
if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value()) auto text_type = text_type_for_code_point(code_point);
while (m_current_index < m_utf8_view.byte_length()) {
code_point = current_code_point();
if (&font != &m_font_cascade_list.font_for_code_point(code_point)) {
if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value())
return result.release_value(); return result.release_value();
} }
if (m_respect_linebreaks && *m_iterator == '\n') { if (m_respect_linebreaks && code_point == '\n') {
// Newline encountered, and we're supposed to preserve them. // Newline encountered, and we're supposed to preserve them.
// If we have accumulated some code points in the current chunk, commit them now and continue with the newline next time. // If we have accumulated some code points in the current chunk, commit them now and continue with the newline next time.
if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value()) if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value())
return result.release_value(); return result.release_value();
// Otherwise, commit the newline! // Otherwise, commit the newline!
++m_iterator; m_current_index = next_grapheme_boundary();
auto result = try_commit_chunk(start_of_chunk, m_iterator, true, font, text_type); auto result = try_commit_chunk(start_of_chunk, m_current_index, true, font, text_type);
VERIFY(result.has_value()); VERIFY(result.has_value());
return result.release_value(); return result.release_value();
} }
if (m_wrap_lines) { if (m_wrap_lines) {
if (text_type != text_type_for_code_point(*m_iterator)) { if (text_type != text_type_for_code_point(code_point)) {
if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value()) if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value()) {
return result.release_value(); return result.release_value();
}
} }
if (is_ascii_space(*m_iterator)) { if (is_ascii_space(code_point)) {
// Whitespace encountered, and we're allowed to break on whitespace. // Whitespace encountered, and we're allowed to break on whitespace.
// If we have accumulated some code points in the current chunk, commit them now and continue with the whitespace next time. // If we have accumulated some code points in the current chunk, commit them now and continue with the whitespace next time.
if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value()) if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value()) {
return result.release_value(); return result.release_value();
}
// Otherwise, commit the whitespace! // Otherwise, commit the whitespace!
++m_iterator; m_current_index = next_grapheme_boundary();
if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value()) if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value())
return result.release_value(); return result.release_value();
continue; continue;
} }
} }
++m_iterator; m_current_index = next_grapheme_boundary();
} }
if (start_of_chunk != m_utf8_view.end()) { if (start_of_chunk != m_utf8_view.byte_length()) {
// Try to output whatever's left at the end of the text node. // Try to output whatever's left at the end of the text node.
if (auto result = try_commit_chunk(start_of_chunk, m_utf8_view.end(), false, font, text_type); result.has_value()) if (auto result = try_commit_chunk(start_of_chunk, m_utf8_view.byte_length(), false, font, text_type); result.has_value())
return result.release_value(); return result.release_value();
} }
return {}; return {};
} }
Optional<TextNode::Chunk> TextNode::ChunkIterator::try_commit_chunk(Utf8View::Iterator const& start, Utf8View::Iterator const& end, bool has_breaking_newline, Gfx::Font const& font, Gfx::GlyphRun::TextType text_type) const Optional<TextNode::Chunk> TextNode::ChunkIterator::try_commit_chunk(size_t start, size_t end, bool has_breaking_newline, Gfx::Font const& font, Gfx::GlyphRun::TextType text_type) const
{ {
auto byte_offset = m_utf8_view.byte_offset_of(start); if (auto byte_length = end - start; byte_length > 0) {
auto byte_length = m_utf8_view.byte_offset_of(end) - byte_offset; auto chunk_view = m_utf8_view.substring_view(start, byte_length);
if (byte_length > 0) {
auto chunk_view = m_utf8_view.substring_view(byte_offset, byte_length);
return Chunk { return Chunk {
.view = chunk_view, .view = chunk_view,
.font = font, .font = font,
.start = byte_offset, .start = start,
.length = byte_length, .length = byte_length,
.has_breaking_newline = has_breaking_newline, .has_breaking_newline = has_breaking_newline,
.is_all_whitespace = is_all_whitespace(chunk_view.as_string()), .is_all_whitespace = is_all_whitespace(chunk_view.as_string()),

10
Userland/Libraries/LibWeb/Layout/TextNode.h
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@ -7,6 +7,7 @@
#pragma once #pragma once
#include <AK/Utf8View.h> #include <AK/Utf8View.h>
#include <LibUnicode/Segmenter.h>
#include <LibWeb/DOM/Text.h> #include <LibWeb/DOM/Text.h>
#include <LibWeb/Layout/Node.h> #include <LibWeb/Layout/Node.h>
@ -38,20 +39,23 @@ public:
class ChunkIterator { class ChunkIterator {
public: public:
ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const&); ChunkIterator(String const& text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const&);
Optional<Chunk> next(); Optional<Chunk> next();
Optional<Chunk> peek(size_t); Optional<Chunk> peek(size_t);
private: private:
Optional<Chunk> next_without_peek(); Optional<Chunk> next_without_peek();
Optional<Chunk> try_commit_chunk(Utf8View::Iterator const& start, Utf8View::Iterator const& end, bool has_breaking_newline, Gfx::Font const&, Gfx::GlyphRun::TextType) const; Optional<Chunk> try_commit_chunk(size_t start, size_t end, bool has_breaking_newline, Gfx::Font const&, Gfx::GlyphRun::TextType) const;
bool const m_wrap_lines; bool const m_wrap_lines;
bool const m_respect_linebreaks; bool const m_respect_linebreaks;
Utf8View m_utf8_view; Utf8View m_utf8_view;
Utf8View::Iterator m_iterator;
Gfx::FontCascadeList const& m_font_cascade_list; Gfx::FontCascadeList const& m_font_cascade_list;
NonnullOwnPtr<Unicode::Segmenter> m_segmenter;
size_t m_current_index { 0 };
Vector<Chunk> m_peek_queue; Vector<Chunk> m_peek_queue;
}; };