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Port raggedness-minimizing line breaking from gl-js.

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This commit is contained in:
Chris Loer
2017-01-05 08:47:02 -08:00
parent 35ccb01dbd
commit 12a9932ebc
7 changed files with 131 additions and 72 deletions
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144
src/mbgl/text/glyph_set.cpp
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@@ -64,7 +64,7 @@ void align(Shaping& shaping,
const float verticalAlign,
const float maxLineLength,
const float lineHeight,
const uint32_t lineCount,
const std::size_t lineCount,
const Point<float>& translate) {
const float shiftX =
(justify - horizontalAlign) * maxLineLength + ::round(translate.x * 24 /* one em */);
@@ -80,8 +80,8 @@ void align(Shaping& shaping,
// justify left = 0, right = 1, center = .5
void justifyLine(std::vector<PositionedGlyph>& positionedGlyphs,
const std::map<uint32_t, SDFGlyph>& sdfs,
uint32_t start,
uint32_t end,
std::size_t start,
std::size_t end,
float justify) {
if (!justify) {
return;
@@ -93,34 +93,104 @@ void justifyLine(std::vector<PositionedGlyph>& positionedGlyphs,
const uint32_t lastAdvance = it->second.metrics.advance;
const float lineIndent = float(glyph.x + lastAdvance) * justify;
for (uint32_t j = start; j <= end; j++) {
for (std::size_t j = start; j <= end; j++) {
positionedGlyphs[j].x -= lineIndent;
}
}
}
float GlyphSet::determineIdeographicLineWidth(const std::u16string& logicalInput,
float GlyphSet::determineAverageLineWidth(const std::u16string& logicalInput,
const float spacing,
float maxWidth) const {
float totalWidth = 0;
// totalWidth doesn't include the last character for magical tuning reasons. This makes the
// algorithm a little more agressive about trying to fit the text into fewer lines, taking
// advantage of the tolerance for going a little over maxWidth
for (uint32_t i = 0; i < logicalInput.size() - 1; i++) {
auto it = sdfs.find(logicalInput[i]);
for (char16_t chr : logicalInput) {
auto it = sdfs.find(chr);
if (it != sdfs.end()) {
totalWidth += it->second.metrics.advance + spacing;
}
}
int32_t lineCount = std::fmax(1, std::ceil(totalWidth / maxWidth));
return totalWidth / lineCount;
int32_t targetLineCount = std::fmax(1, std::ceil(totalWidth / maxWidth));
return totalWidth / targetLineCount;
}
float calculateBadness(const float lineWidth, const float targetWidth, const float penalty, const bool isLastBreak) {
const float raggedness = std::pow(lineWidth - targetWidth, 2);
if (isLastBreak && lineWidth < targetWidth) {
// Be more tolerant of short final lines
return std::fmax(0, raggedness - 150);
}
if (penalty < 0) {
return raggedness - std::pow(penalty, 2);
}
return raggedness + std::pow(penalty, 2);
}
float calculatePenalty(char16_t codePoint, char16_t previousCodePoint) {
float penalty = 0;
// Force break on newline
if (codePoint == 0x0a) {
penalty -= 10000;
}
// Penalize open parenthesis at end of line
if (previousCodePoint && (previousCodePoint == 0x28 || previousCodePoint == 0xff08)) {
penalty += 50;
}
// Penalize close parenthesis at beginning of line
if (codePoint == 0x29 || codePoint == 0xff09) {
penalty += 50;
}
return penalty;
}
struct PotentialBreak {
PotentialBreak(const std::size_t p_index, const float p_x, const PotentialBreak* p_priorBreak, const float p_badness)
: index(p_index), x(p_x), priorBreak(p_priorBreak), badness(p_badness)
{}
const std::size_t index;
const float x;
const PotentialBreak* priorBreak;
const float badness;
};
PotentialBreak evaluateBreak(const std::size_t breakIndex, const float breakX, const float targetWidth, const std::list<PotentialBreak>& potentialBreaks, const float penalty, const bool isLastBreak) {
// We could skip evaluating breaks where the line length (breakX - priorBreak.x) > maxWidth
// ...but in fact we allow lines longer than maxWidth (if there's no break points)
// ...and when targetWidth and maxWidth are close, strictly enforcing maxWidth can give
// more lopsided results.
const PotentialBreak* bestPriorBreak = nullptr;
float bestBreakBadness = calculateBadness(breakX, targetWidth, penalty, isLastBreak);
for (const auto& potentialBreak : potentialBreaks) {
const float lineWidth = breakX - potentialBreak.x;
float breakBadness = calculateBadness(lineWidth, targetWidth, penalty, isLastBreak) + potentialBreak.badness;
if (breakBadness <= bestBreakBadness) {
bestPriorBreak = &potentialBreak;
bestBreakBadness = breakBadness;
}
}
return PotentialBreak(breakIndex, breakX, bestPriorBreak, bestBreakBadness);
}
std::set<std::size_t> leastBadBreaks(const PotentialBreak& lastLineBreak) {
std::set<std::size_t> leastBadBreaks = { lastLineBreak.index };
const PotentialBreak* priorBreak = lastLineBreak.priorBreak;
while (priorBreak) {
leastBadBreaks.insert(priorBreak->index);
priorBreak = priorBreak->priorBreak;
}
return leastBadBreaks;
}
// We determine line breaks based on shaped text in logical order. Working in visual order would be
// more intuitive, but we can't do that because the visual order may be changed by line breaks!
std::set<int32_t> GlyphSet::determineLineBreaks(const std::u16string& logicalInput,
std::set<std::size_t> GlyphSet::determineLineBreaks(const std::u16string& logicalInput,
const float spacing,
float maxWidth) const {
if (!maxWidth) {
@@ -130,42 +200,34 @@ std::set<int32_t> GlyphSet::determineLineBreaks(const std::u16string& logicalInp
if (logicalInput.empty()) {
return {};
}
if (util::i18n::allowsIdeographicBreaking(logicalInput)) {
maxWidth = determineIdeographicLineWidth(logicalInput, spacing, maxWidth);
}
std::set<int32_t> lineBreakPoints;
const float targetWidth = determineAverageLineWidth(logicalInput, spacing, maxWidth);
std::list<PotentialBreak> potentialBreaks;
float currentX = 0;
uint32_t lastSafeBreak = 0;
float lastSafeBreakX = 0;
for (uint32_t i = 0; i < logicalInput.size(); i++) {
auto it = sdfs.find(logicalInput[i]);
for (std::size_t i = 0; i < logicalInput.size(); i++) {
const char16_t codePoint = logicalInput[i];
auto it = sdfs.find(codePoint);
if (it == sdfs.end()) {
continue;
}
const SDFGlyph& glyph = it->second;
// Ideographic characters, spaces, and word-breaking punctuation that often appear without
// surrounding spaces.
if (util::i18n::allowsWordBreaking(glyph.id) ||
util::i18n::allowsIdeographicBreaking(glyph.id)) {
lastSafeBreak = i;
lastSafeBreakX = currentX;
if (util::i18n::allowsWordBreaking(codePoint) ||
util::i18n::allowsIdeographicBreaking(codePoint)) {
const char16_t previousCodePoint = i > 0 ? logicalInput[i-1] : 0;
potentialBreaks.push_back(evaluateBreak(i, currentX, targetWidth, potentialBreaks,
calculatePenalty(codePoint, previousCodePoint),
false));
}
if (currentX > maxWidth && lastSafeBreak > 0) {
lineBreakPoints.insert(lastSafeBreak);
currentX -= lastSafeBreakX;
lastSafeBreakX = 0;
}
currentX += glyph.metrics.advance + spacing;
currentX += it->second.metrics.advance + spacing;
}
return lineBreakPoints;
return leastBadBreaks(evaluateBreak(logicalInput.size(), currentX, targetWidth, potentialBreaks, 0, true));
}
void GlyphSet::shapeLines(Shaping& shaping,
@@ -194,7 +256,7 @@ void GlyphSet::shapeLines(Shaping& shaping,
continue;
}
uint32_t lineStartIndex = static_cast<uint32_t>(shaping.positionedGlyphs.size());
std::size_t lineStartIndex = shaping.positionedGlyphs.size();
for (char16_t chr : line) {
auto it = sdfs.find(chr);
if (it == sdfs.end()) {
@@ -207,12 +269,12 @@ void GlyphSet::shapeLines(Shaping& shaping,
}
// Only justify if we placed at least one glyph
if (static_cast<uint32_t>(shaping.positionedGlyphs.size()) != lineStartIndex) {
if (shaping.positionedGlyphs.size() != lineStartIndex) {
float lineLength = x - spacing; // Don't count trailing spacing
maxLineLength = util::max(lineLength, maxLineLength);
justifyLine(shaping.positionedGlyphs, sdfs, lineStartIndex,
static_cast<uint32_t>(shaping.positionedGlyphs.size()) - 1, justify);
shaping.positionedGlyphs.size() - 1, justify);
}
x = 0;
@@ -220,7 +282,7 @@ void GlyphSet::shapeLines(Shaping& shaping,
}
align(shaping, justify, horizontalAlign, verticalAlign, maxLineLength, lineHeight,
static_cast<uint32_t>(lines.size()), translate);
lines.size(), translate);
const uint32_t height = lines.size() * lineHeight;
// Calculate the bounding box