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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 "SkBitSet.h"
#include "SkPDFMakeCIDGlyphWidthsArray.h"
#include "SkPaint.h"
#include "SkGlyphCache.h"
// TODO(halcanary): Write unit tests for SkPDFMakeCIDGlyphWidthsArray().
// TODO(halcanary): The logic in this file originated in several
// disparate places. I feel sure that someone could simplify this
// down to a single easy-to-read function.
namespace {
struct AdvanceMetric {
enum MetricType {
kDefault, // Default advance: fAdvance.count = 1
kRange, // Advances for a range: fAdvance.count = fEndID-fStartID
kRun // fStartID-fEndID have same advance: fAdvance.count = 1
};
MetricType fType;
uint16_t fStartId;
uint16_t fEndId;
SkTDArray<int16_t> fAdvance;
AdvanceMetric(uint16_t startId) : fStartId(startId) {}
AdvanceMetric(AdvanceMetric&&) = default;
AdvanceMetric& operator=(AdvanceMetric&& other) = default;
AdvanceMetric(const AdvanceMetric&) = delete;
AdvanceMetric& operator=(const AdvanceMetric&) = delete;
};
const int16_t kInvalidAdvance = SK_MinS16;
const int16_t kDontCareAdvance = SK_MinS16 + 1;
} // namespace
// scale from em-units to base-1000, returning as a SkScalar
static SkScalar from_font_units(SkScalar scaled, uint16_t emSize) {
if (emSize == 1000) {
return scaled;
} else {
return scaled * 1000 / emSize;
}
}
static SkScalar scale_from_font_units(int16_t val, uint16_t emSize) {
return from_font_units(SkIntToScalar(val), emSize);
}
static void strip_uninteresting_trailing_advances_from_range(
AdvanceMetric* range) {
SkASSERT(range);
int expectedAdvanceCount = range->fEndId - range->fStartId + 1;
if (range->fAdvance.count() < expectedAdvanceCount) {
return;
}
for (int i = expectedAdvanceCount - 1; i >= 0; --i) {
if (range->fAdvance[i] != kDontCareAdvance &&
range->fAdvance[i] != kInvalidAdvance &&
range->fAdvance[i] != 0) {
range->fEndId = range->fStartId + i;
break;
}
}
}
static void zero_wildcards_in_range(AdvanceMetric* range) {
SkASSERT(range);
if (range->fType != AdvanceMetric::kRange) {
return;
}
SkASSERT(range->fAdvance.count() == range->fEndId - range->fStartId + 1);
// Zero out wildcards.
for (int i = 0; i < range->fAdvance.count(); ++i) {
if (range->fAdvance[i] == kDontCareAdvance) {
range->fAdvance[i] = 0;
}
}
}
static void finish_range(
AdvanceMetric* range,
int endId,
AdvanceMetric::MetricType type) {
range->fEndId = endId;
range->fType = type;
strip_uninteresting_trailing_advances_from_range(range);
int newLength;
if (type == AdvanceMetric::kRange) {
newLength = range->fEndId - range->fStartId + 1;
} else {
if (range->fEndId == range->fStartId) {
range->fType = AdvanceMetric::kRange;
}
newLength = 1;
}
SkASSERT(range->fAdvance.count() >= newLength);
range->fAdvance.setCount(newLength);
zero_wildcards_in_range(range);
}
static void compose_advance_data(const AdvanceMetric& range,
uint16_t emSize,
int16_t* defaultAdvance,
SkPDFArray* result) {
switch (range.fType) {
case AdvanceMetric::kDefault: {
SkASSERT(range.fAdvance.count() == 1);
*defaultAdvance = range.fAdvance[0];
break;
}
case AdvanceMetric::kRange: {
auto advanceArray = sk_make_sp<SkPDFArray>();
for (int j = 0; j < range.fAdvance.count(); j++)
advanceArray->appendScalar(
scale_from_font_units(range.fAdvance[j], emSize));
result->appendInt(range.fStartId);
result->appendObject(std::move(advanceArray));
break;
}
case AdvanceMetric::kRun: {
SkASSERT(range.fAdvance.count() == 1);
result->appendInt(range.fStartId);
result->appendInt(range.fEndId);
result->appendScalar(
scale_from_font_units(range.fAdvance[0], emSize));
break;
}
}
}
/** Retrieve advance data for glyphs. Used by the PDF backend. */
// TODO(halcanary): this function is complex enough to need its logic
// tested with unit tests.
sk_sp<SkPDFArray> SkPDFMakeCIDGlyphWidthsArray(SkGlyphCache* cache,
const SkBitSet* subset,
uint16_t emSize,
int16_t* defaultAdvance) {
// Assuming that on average, the ASCII representation of an advance plus
// a space is 8 characters and the ASCII representation of a glyph id is 3
// characters, then the following cut offs for using different range types
// apply:
// The cost of stopping and starting the range is 7 characers
// a. Removing 4 0's or don't care's is a win
// The cost of stopping and starting the range plus a run is 22
// characters
// b. Removing 3 repeating advances is a win
// c. Removing 2 repeating advances and 3 don't cares is a win
// When not currently in a range the cost of a run over a range is 16
// characaters, so:
// d. Removing a leading 0/don't cares is a win because it is omitted
// e. Removing 2 repeating advances is a win
auto result = sk_make_sp<SkPDFArray>();
int num_glyphs = SkToInt(cache->getGlyphCount());
bool prevRange = false;
int16_t lastAdvance = kInvalidAdvance;
int repeatedAdvances = 0;
int wildCardsInRun = 0;
int trailingWildCards = 0;
// Limit the loop count to glyph id ranges provided.
int lastIndex = num_glyphs;
if (subset) {
while (!subset->has(lastIndex - 1) && lastIndex > 0) {
--lastIndex;
}
}
AdvanceMetric curRange(0);
for (int gId = 0; gId <= lastIndex; gId++) {
int16_t advance = kInvalidAdvance;
if (gId < lastIndex) {
if (!subset || 0 == gId || subset->has(gId)) {
advance = (int16_t)cache->getGlyphIDAdvance(gId).fAdvanceX;
} else {
advance = kDontCareAdvance;
}
}
if (advance == lastAdvance) {
repeatedAdvances++;
trailingWildCards = 0;
} else if (advance == kDontCareAdvance) {
wildCardsInRun++;
trailingWildCards++;
} else if (curRange.fAdvance.count() ==
repeatedAdvances + 1 + wildCardsInRun) { // All in run.
if (lastAdvance == 0) {
curRange.fStartId = gId; // reset
curRange.fAdvance.setCount(0);
trailingWildCards = 0;
} else if (repeatedAdvances + 1 >= 2 || trailingWildCards >= 4) {
finish_range(&curRange, gId - 1, AdvanceMetric::kRun);
compose_advance_data(curRange, emSize, defaultAdvance, result.get());
prevRange = true;
curRange = AdvanceMetric(gId);
trailingWildCards = 0;
}
repeatedAdvances = 0;
wildCardsInRun = trailingWildCards;
trailingWildCards = 0;
} else {
if (lastAdvance == 0 &&
repeatedAdvances + 1 + wildCardsInRun >= 4) {
finish_range(&curRange,
gId - repeatedAdvances - wildCardsInRun - 2,
AdvanceMetric::kRange);
compose_advance_data(curRange, emSize, defaultAdvance, result.get());
prevRange = true;
curRange = AdvanceMetric(gId);
trailingWildCards = 0;
} else if (trailingWildCards >= 4 && repeatedAdvances + 1 < 2) {
finish_range(&curRange, gId - trailingWildCards - 1,
AdvanceMetric::kRange);
compose_advance_data(curRange, emSize, defaultAdvance, result.get());
prevRange = true;
curRange = AdvanceMetric(gId);
trailingWildCards = 0;
} else if (lastAdvance != 0 &&
(repeatedAdvances + 1 >= 3 ||
(repeatedAdvances + 1 >= 2 && wildCardsInRun >= 3))) {
finish_range(&curRange,
gId - repeatedAdvances - wildCardsInRun - 2,
AdvanceMetric::kRange);
compose_advance_data(curRange, emSize, defaultAdvance, result.get());
curRange =
AdvanceMetric(gId - repeatedAdvances - wildCardsInRun - 1);
curRange.fAdvance.append(1, &lastAdvance);
finish_range(&curRange, gId - 1, AdvanceMetric::kRun);
compose_advance_data(curRange, emSize, defaultAdvance, result.get());
prevRange = true;
curRange = AdvanceMetric(gId);
trailingWildCards = 0;
}
repeatedAdvances = 0;
wildCardsInRun = trailingWildCards;
trailingWildCards = 0;
}
curRange.fAdvance.append(1, &advance);
if (advance != kDontCareAdvance) {
lastAdvance = advance;
}
}
if (curRange.fStartId == lastIndex) {
if (!prevRange) {
return nullptr; // https://crbug.com/567031
}
} else {
finish_range(&curRange, lastIndex - 1, AdvanceMetric::kRange);
compose_advance_data(curRange, emSize, defaultAdvance, result.get());
}
return result;
}