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libtxt: handle characters encoded as multiple UTF-16 code units (flut…
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…ter#4165)
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@jason-simmons
jason-simmons authored Oct 3, 2017
1 parent 0448bf9 commit 414c3fe
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Showing 2 changed files with 84 additions and 43 deletions.
106 changes: 67 additions & 39 deletions third_party/txt/src/txt/paragraph.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
#include <hb.h>
#include <algorithm>
#include <limits>
#include <numeric>
#include <tuple>
#include <utility>
#include <vector>
Expand Down Expand Up @@ -118,6 +119,30 @@ void GetPaint(const TextStyle& style, SkPaint* paint) {

static const float kDoubleDecorationSpacing = 3.0f;

Paragraph::GlyphLine::GlyphLine(std::vector<GlyphPosition>&& p)
: positions(std::move(p)),
total_code_units(std::accumulate(
positions.begin(),
positions.end(),
0,
[](size_t a, const auto& b) { return a + b.code_units; })) {}

const Paragraph::GlyphPosition& Paragraph::GlyphLine::GetGlyphPosition(
size_t pos) const {
FXL_DCHECK(pos < total_code_units);
if (positions.size() == total_code_units)
return positions[pos];

size_t unit_count = 0;
for (const Paragraph::GlyphPosition& gp : positions) {
if (pos < unit_count + gp.code_units)
return gp;
unit_count += gp.code_units;
}

return positions.back();
}

Paragraph::Paragraph() = default;

Paragraph::~Paragraph() = default;
Expand Down Expand Up @@ -224,7 +249,7 @@ void Paragraph::Layout(double width, bool force) {
line_heights_ = std::vector<double>();
records_ = std::vector<PaintRecord>();

glyph_position_x_ = std::vector<std::vector<GlyphPosition>>();
glyph_position_x_ = std::vector<GlyphLine>();
std::vector<GlyphPosition> glyph_single_line_position_x;

SkScalar x_offset = GetLineXOffset(0);
Expand All @@ -235,8 +260,6 @@ void Paragraph::Layout(double width, bool force) {
double prev_max_descent = 0.0f;
std::vector<SkScalar> x_queue;
double justify_spacing = 0.0f;
double prev_word_pos = 0.0f;
double prev_char_advance = 0.0f;
double current_x_position = 0.0f;

std::vector<const SkTextBlobBuilder::RunBuffer*> buffers;
Expand Down Expand Up @@ -324,7 +347,7 @@ void Paragraph::Layout(double width, bool force) {

const size_t glyph_count = layout.nGlyphs();
size_t blob_start = 0;
size_t character_index = 0;
size_t code_unit_index = 0;

// Each blob.
buffers = std::vector<const SkTextBlobBuilder::RunBuffer*>();
Expand Down Expand Up @@ -368,30 +391,37 @@ void Paragraph::Layout(double width, bool force) {
buffers.back()->pos[pos_index] = current_x_position + letter_spacing;
buffers.back()->pos[pos_index + 1] = layout.getY(glyph_index);

float glyph_advance = layout.getCharAdvance(character_index);
float glyph_advance = layout.getCharAdvance(code_unit_index);

// The glyph may be a ligature. Determine how many input characters
// are joined into this glyph.
size_t ligature_end = character_index + 1;
for (; ligature_end < text_count; ++ligature_end) {
if (layout.getCharAdvance(ligature_end) != 0)
// are joined into this glyph. Note that each character may be
// encoded as multiple UTF-16 code units.
size_t prev_code_unit_index = code_unit_index;
U16_FWD_1(text_ptr, code_unit_index, text_count);
std::vector<size_t> subglyph_code_unit_counts{code_unit_index -
prev_code_unit_index};
while (code_unit_index < text_count) {
if (layout.getCharAdvance(code_unit_index) != 0)
break;
prev_code_unit_index = code_unit_index;
U16_FWD_1(text_ptr, code_unit_index, text_count);
subglyph_code_unit_counts.push_back(code_unit_index -
prev_code_unit_index);
}
size_t ligature_width = ligature_end - character_index;
float subglyph_advance = glyph_advance / ligature_width;
float subglyph_advance =
glyph_advance / subglyph_code_unit_counts.size();
glyph_single_line_position_x.emplace_back(
x_offset + current_x_position + letter_spacing, subglyph_advance);
x_offset + current_x_position + letter_spacing, subglyph_advance,
subglyph_code_unit_counts[0]);

// Compute positions for the additional characters in the ligature.
for (size_t i = 1; i < ligature_width; ++i) {
for (size_t i = 1; i < subglyph_code_unit_counts.size(); ++i) {
glyph_single_line_position_x.emplace_back(
glyph_single_line_position_x.back().start + subglyph_advance,
subglyph_advance);
subglyph_advance, subglyph_code_unit_counts[i]);
}

current_x_position += glyph_advance;
character_index += ligature_width;
prev_char_advance = subglyph_advance;

// Check if the current Glyph is a whitespace and handle multiple
// whitespaces in a row.
Expand Down Expand Up @@ -453,19 +483,18 @@ void Paragraph::Layout(double width, bool force) {
line_heights_.push_back(
(line_heights_.empty() ? 0 : line_heights_.back()) +
roundf(max_line_spacing + max_descent));
glyph_position_x_.push_back(glyph_single_line_position_x);
glyph_position_x_.emplace_back(std::move(glyph_single_line_position_x));
glyph_single_line_position_x.clear();

prev_max_descent = max_descent;

// Reset Variables for next line.
max_line_spacing = 0.0f;
max_descent = 0.0f;
prev_word_pos = 0;
prev_char_advance = 0.0f;
current_x_position = 0.0f;
break_index += 1;
lines_++;
x_offset = GetLineXOffset(lines_);
glyph_single_line_position_x.clear();
} else {
x_offset += layout.getAdvance();
}
Expand Down Expand Up @@ -780,33 +809,33 @@ std::vector<SkRect> Paragraph::GetRectsForRange(size_t start,
size_t pos = 0;
size_t line;
for (line = 0; line < glyph_position_x_.size(); ++line) {
if (start < pos + glyph_position_x_[line].size())
if (start < pos + glyph_position_x_[line].total_code_units)
break;
pos += glyph_position_x_[line].size();
pos += glyph_position_x_[line].total_code_units;
}
if (line == glyph_position_x_.size())
return rects;

if (end <= pos + glyph_position_x_[line].size()) {
if (end <= pos + glyph_position_x_[line].total_code_units) {
rects.push_back(GetRectForLineRange(line, start - pos, end - pos));
return rects;
}

rects.push_back(
GetRectForLineRange(line, start - pos, glyph_position_x_[line].size()));
rects.push_back(GetRectForLineRange(
line, start - pos, glyph_position_x_[line].total_code_units));

while (true) {
pos += glyph_position_x_[line].size();
pos += glyph_position_x_[line].total_code_units;
line++;
if (line == glyph_position_x_.size())
break;

if (end <= pos + glyph_position_x_[line].size()) {
if (end <= pos + glyph_position_x_[line].total_code_units) {
rects.push_back(GetRectForLineRange(line, 0, end - pos));
break;
} else {
rects.push_back(
GetRectForLineRange(line, 0, glyph_position_x_[line].size()));
rects.push_back(GetRectForLineRange(
line, 0, glyph_position_x_[line].total_code_units));
}
}

Expand All @@ -817,15 +846,14 @@ SkRect Paragraph::GetRectForLineRange(size_t line,
size_t start,
size_t end) const {
FXL_DCHECK(line < glyph_position_x_.size());
const std::vector<GlyphPosition>& line_glyph_position =
glyph_position_x_[line];
if (line_glyph_position.empty())
const GlyphLine& glyph_line = glyph_position_x_[line];
if (glyph_line.positions.empty())
return SkRect::MakeEmpty();

FXL_DCHECK(start < line_glyph_position.size());
SkScalar left = line_glyph_position[start].start;
end = std::min(end, line_glyph_position.size());
SkScalar right = line_glyph_position[end - 1].glyph_end();
FXL_DCHECK(start < glyph_line.total_code_units);
SkScalar left = glyph_line.GetGlyphPosition(start).start;
end = std::min(end, glyph_line.total_code_units);
SkScalar right = glyph_line.GetGlyphPosition(end - 1).glyph_end();
SkScalar top = (line > 0) ? line_heights_[line - 1] : 0;
SkScalar bottom = line_heights_[line];
return SkRect::MakeLTRB(left, top, right, bottom);
Expand All @@ -843,11 +871,11 @@ Paragraph::PositionWithAffinity Paragraph::GetGlyphPositionAtCoordinate(
for (y_index = 0; y_index < line_heights_.size() - 1; ++y_index) {
if (dy < line_heights_[y_index])
break;
offset += glyph_position_x_[y_index].size();
offset += glyph_position_x_[y_index].total_code_units;
}

const std::vector<GlyphPosition>& line_glyph_position =
glyph_position_x_[y_index];
glyph_position_x_[y_index].positions;
size_t x_index;
for (x_index = 0; x_index < line_glyph_position.size(); ++x_index) {
double glyph_end = (x_index < line_glyph_position.size() - 1)
Expand All @@ -863,7 +891,7 @@ Paragraph::PositionWithAffinity Paragraph::GetGlyphPositionAtCoordinate(
if (dx < boundary)
break;

offset++;
offset += line_glyph_position[x_index].code_units;
}
return PositionWithAffinity(offset, x_index > 0 ? UPSTREAM : DOWNSTREAM);
}
Expand Down
21 changes: 17 additions & 4 deletions third_party/txt/src/txt/paragraph.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -188,16 +188,29 @@ class Paragraph {
std::vector<double> line_heights_;

struct GlyphPosition {
double start;
double advance;
const double start;
const double advance;
const size_t code_units;

GlyphPosition(double s, double a) : start(s), advance(a) {}
GlyphPosition(double s, double a, size_t cu)
: start(s), advance(a), code_units(cu) {}

double glyph_end() const { return start + advance; }
};

struct GlyphLine {
const std::vector<GlyphPosition> positions;
const size_t total_code_units;

GlyphLine(std::vector<GlyphPosition>&& p);

// Return the GlyphPosition containing the given code unit index within
// the line.
const GlyphPosition& GetGlyphPosition(size_t pos) const;
};

// Holds the laid out x positions of each glyph.
std::vector<std::vector<GlyphPosition>> glyph_position_x_;
std::vector<GlyphLine> glyph_position_x_;

// Set of glyph IDs that correspond to whitespace.
std::set<GlyphID> whitespace_set_;
Expand Down

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