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/*
* Copyright 2016 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "src/pdf/SkPDFMakeCIDGlyphWidthsArray.h"
#include "include/core/SkPaint.h"
#include "include/private/base/SkTo.h"
#include "src/core/SkStrike.h"
#include "src/core/SkStrikeSpec.h"
#include "src/pdf/SkPDFGlyphUse.h"
#include <algorithm>
#include <vector>
namespace {
// Scale from em-units to 1000-units.
SkScalar from_font_units(SkScalar scaled, uint16_t emSize) {
if (emSize == 1000) {
return scaled;
} else {
return scaled * 1000 / emSize;
}
}
SkScalar find_mode_or_0(SkSpan<const SkScalar> advances) {
if (advances.empty()) {
return 0;
}
SkScalar currentAdvance = advances[0];
SkScalar currentModeAdvance = advances[0];
size_t currentCount = 1;
size_t currentModeCount = 1;
for (size_t i = 1; i < advances.size(); ++i) {
if (advances[i] == currentAdvance) {
++currentCount;
} else {
if (currentCount > currentModeCount) {
currentModeAdvance = currentAdvance;
currentModeCount = currentCount;
}
currentAdvance = advances[i];
currentCount = 1;
}
}
return currentCount > currentModeCount ? currentAdvance : currentModeAdvance;
}
} // namespace
std::unique_ptr<SkPDFArray> SkPDFMakeCIDGlyphWidthsArray(const SkTypeface& typeface,
const SkPDFGlyphUse& subset,
int32_t* defaultAdvance) {
// There are two ways of expressing advances
//
// range: " gfid [adv.ances adv.ances ... adv.ances]"
// run: " gfid gfid adv.ances"
//
// Assuming that on average
// the ASCII representation of an advance plus a space is 10 characters
// the ASCII representation of a glyph id plus a space is 4 characters
// the ASCII representation of unused gid plus a space in a range is 2 characters
//
// When not in a range or run
// a. Skipping don't cares or defaults is a win (trivial)
// b. Run wins for 2+ repeats " gid gid adv.ances"
// " gid [adv.ances adv.ances]"
// rule: 2+ repeats create run as long as possible, else start range
//
// When in a range
// Cost of stopping and starting a range is 8 characters "] gid ["
// c. Skipping defaults is always a win " adv.ances"
// rule: end range if default seen
// d. Skipping 4+ don't cares is a win " 0 0 0 0"
// rule: end range if 4+ don't cares
// Cost of stop and start range plus run is 28 characters "] gid gid adv.ances gid ["
// e. Switching for 2+ repeats and 4+ don't cares wins " 0 0 adv.ances 0 0 adv.ances"
// rule: end range for 2+ repeats with 4+ don't cares
// f. Switching for 3+ repeats wins " adv.ances adv.ances adv.ances"
// rule: end range for 3+ repeats
int emSize;
SkStrikeSpec strikeSpec = SkStrikeSpec::MakePDFVector(typeface, &emSize);
SkBulkGlyphMetricsAndPaths paths{strikeSpec};
auto result = SkPDFMakeArray();
std::vector<SkGlyphID> glyphIDs;
subset.getSetValues([&](unsigned index) {
glyphIDs.push_back(SkToU16(index));
});
auto glyphs = paths.glyphs(SkSpan(glyphIDs));
// C++20 = make_unique_for_overwrite<SkScalar[]>(glyphs.size());
auto advances = std::unique_ptr<SkScalar[]>(new SkScalar[glyphs.size()]);
// Find the pdf integer mode (most common pdf integer advance).
// Unfortunately, poppler enforces DW (default width) must be an integer,
// so only consider integer pdf advances when finding the mode.
size_t numIntAdvances = 0;
for (const SkGlyph* glyph : glyphs) {
SkScalar currentAdvance = from_font_units(glyph->advanceX(), emSize);
if ((int32_t)currentAdvance == currentAdvance) {
advances[numIntAdvances++] = currentAdvance;
}
}
std::sort(advances.get(), advances.get() + numIntAdvances);
int32_t modeAdvance = (int32_t)find_mode_or_0(SkSpan(advances.get(), numIntAdvances));
*defaultAdvance = modeAdvance;
// Pre-convert to pdf advances.
for (size_t i = 0; i < glyphs.size(); ++i) {
advances[i] = from_font_units(glyphs[i]->advanceX(), emSize);
}
for (size_t i = 0; i < glyphs.size(); ++i) {
SkScalar advance = advances[i];
// a. Skipping don't cares or defaults is a win (trivial)
if (advance == modeAdvance) {
continue;
}
// b. 2+ repeats create run as long as possible, else start range
{
size_t j = i + 1; // j is always one past the last known repeat
for (; j < glyphs.size(); ++j) {
SkScalar next_advance = advances[j];
if (advance != next_advance) {
break;
}
}
if (j - i >= 2) {
result->appendInt(glyphs[i]->getGlyphID());
result->appendInt(glyphs[j - 1]->getGlyphID());
result->appendScalar(advance);
i = j - 1;
continue;
}
}
{
result->appendInt(glyphs[i]->getGlyphID());
auto advanceArray = SkPDFMakeArray();
advanceArray->appendScalar(advance);
size_t j = i + 1; // j is always one past the last output
for (; j < glyphs.size(); ++j) {
advance = advances[j];
// c. end range if default seen
if (advance == modeAdvance) {
break;
}
int dontCares = glyphs[j]->getGlyphID() - glyphs[j - 1]->getGlyphID() - 1;
// d. end range if 4+ don't cares
if (dontCares >= 4) {
break;
}
SkScalar next_advance = 0;
// e. end range for 2+ repeats with 4+ don't cares
if (j + 1 < glyphs.size()) {
next_advance = advances[j+1];
int next_dontCares = glyphs[j+1]->getGlyphID() - glyphs[j]->getGlyphID() - 1;
if (advance == next_advance && dontCares + next_dontCares >= 4) {
break;
}
}
// f. end range for 3+ repeats
if (j + 2 < glyphs.size() && advance == next_advance) {
next_advance = advances[j+2];
if (advance == next_advance) {
break;
}
}
while (dontCares --> 0) {
advanceArray->appendScalar(0);
}
advanceArray->appendScalar(advance);
}
result->appendObject(std::move(advanceArray));
i = j - 1;
}
}
return result;
}
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