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Move DistanceAdjustTable to its own file

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BUG=skia:

Review URL: https://codereview.chromium.org/1512823004
This commit is contained in:
joshualitt 2015-12-10 09:10:10 -08:00 committed by Commit bot
parent f10ecb71a9
commit 1acabf3787
6 changed files with 136 additions and 111 deletions
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2
gyp/gpu.gypi
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@ -82,6 +82,8 @@
'<(skia_src_path)/gpu/GrCoordTransform.cpp',
'<(skia_src_path)/gpu/GrDefaultGeoProcFactory.cpp',
'<(skia_src_path)/gpu/GrDefaultGeoProcFactory.h',
'<(skia_src_path)/gpu/GrDistanceFieldAdjustTable.cpp',
'<(skia_src_path)/gpu/GrDistanceFieldAdjustTable.h',
'<(skia_src_path)/gpu/GrDrawContext.cpp',
'<(skia_src_path)/gpu/GrDrawingManager.cpp',
'<(skia_src_path)/gpu/GrDrawingManager.h',

85
src/gpu/GrAtlasTextContext.cpp
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@ -46,13 +46,11 @@ static const int kLargeDFFontLimit = 384;
#else
static const int kLargeDFFontLimit = 2 * kLargeDFFontSize;
#endif
SkDEBUGCODE(static const int kExpectedDistanceAdjustTableSize = 8;)
};
GrAtlasTextContext::GrAtlasTextContext(GrContext* context, const SkSurfaceProps& surfaceProps)
: INHERITED(context, surfaceProps)
, fDistanceAdjustTable(new DistanceAdjustTable) {
, fDistanceAdjustTable(new GrDistanceFieldAdjustTable) {
// We overallocate vertices in our textblobs based on the assumption that A8 has the greatest
// vertexStride
static_assert(GrAtlasTextBlob::kGrayTextVASize >= GrAtlasTextBlob::kColorTextVASize &&
@ -62,87 +60,6 @@ GrAtlasTextContext::GrAtlasTextContext(GrContext* context, const SkSurfaceProps&
fCache = context->getTextBlobCache();
}
void GrAtlasTextContext::DistanceAdjustTable::buildDistanceAdjustTable() {
// This is used for an approximation of the mask gamma hack, used by raster and bitmap
// text. The mask gamma hack is based off of guessing what the blend color is going to
// be, and adjusting the mask so that when run through the linear blend will
// produce the value closest to the desired result. However, in practice this means
// that the 'adjusted' mask is just increasing or decreasing the coverage of
// the mask depending on what it is thought it will blit against. For black (on
// assumed white) this means that coverages are decreased (on a curve). For white (on
// assumed black) this means that coverages are increased (on a a curve). At
// middle (perceptual) gray (which could be blit against anything) the coverages
// remain the same.
//
// The idea here is that instead of determining the initial (real) coverage and
// then adjusting that coverage, we determine an adjusted coverage directly by
// essentially manipulating the geometry (in this case, the distance to the glyph
// edge). So for black (on assumed white) this thins a bit; for white (on
// assumed black) this fake bolds the geometry a bit.
//
// The distance adjustment is calculated by determining the actual coverage value which
// when fed into in the mask gamma table gives us an 'adjusted coverage' value of 0.5. This
// actual coverage value (assuming it's between 0 and 1) corresponds to a distance from the
// actual edge. So by subtracting this distance adjustment and computing without the
// the coverage adjustment we should get 0.5 coverage at the same point.
//
// This has several implications:
// For non-gray lcd smoothed text, each subpixel essentially is using a
// slightly different geometry.
//
// For black (on assumed white) this may not cover some pixels which were
// previously covered; however those pixels would have been only slightly
// covered and that slight coverage would have been decreased anyway. Also, some pixels
// which were previously fully covered may no longer be fully covered.
//
// For white (on assumed black) this may cover some pixels which weren't
// previously covered at all.
int width, height;
size_t size;
#ifdef SK_GAMMA_CONTRAST
SkScalar contrast = SK_GAMMA_CONTRAST;
#else
SkScalar contrast = 0.5f;
#endif
SkScalar paintGamma = SK_GAMMA_EXPONENT;
SkScalar deviceGamma = SK_GAMMA_EXPONENT;
size = SkScalerContext::GetGammaLUTSize(contrast, paintGamma, deviceGamma,
&width, &height);
SkASSERT(kExpectedDistanceAdjustTableSize == height);
fTable = new SkScalar[height];
SkAutoTArray<uint8_t> data((int)size);
SkScalerContext::GetGammaLUTData(contrast, paintGamma, deviceGamma, data.get());
// find the inverse points where we cross 0.5
// binsearch might be better, but we only need to do this once on creation
for (int row = 0; row < height; ++row) {
uint8_t* rowPtr = data.get() + row*width;
for (int col = 0; col < width - 1; ++col) {
if (rowPtr[col] <= 127 && rowPtr[col + 1] >= 128) {
// compute point where a mask value will give us a result of 0.5
float interp = (127.5f - rowPtr[col]) / (rowPtr[col + 1] - rowPtr[col]);
float borderAlpha = (col + interp) / 255.f;
// compute t value for that alpha
// this is an approximate inverse for smoothstep()
float t = borderAlpha*(borderAlpha*(4.0f*borderAlpha - 6.0f) + 5.0f) / 3.0f;
// compute distance which gives us that t value
const float kDistanceFieldAAFactor = 0.65f; // should match SK_DistanceFieldAAFactor
float d = 2.0f*kDistanceFieldAAFactor*t - kDistanceFieldAAFactor;
fTable[row] = d;
break;
}
}
}
}
GrAtlasTextContext* GrAtlasTextContext::Create(GrContext* context,
const SkSurfaceProps& surfaceProps) {

23
src/gpu/GrAtlasTextContext.h
View File

@ -11,6 +11,7 @@
#include "GrTextContext.h"
#include "GrAtlasTextBlob.h"
#include "GrDistanceFieldAdjustTable.h"
#include "GrGeometryProcessor.h"
#include "SkTextBlobRunIterator.h"
@ -148,29 +149,9 @@ private:
const SkPoint& offset,
const SkIRect& regionClipBounds);
// Distance field text needs this table to compute a value for use in the fragment shader.
// Because the GrAtlasTextContext can go out of scope before the final flush, this needs to be
// refcnted and malloced
struct DistanceAdjustTable : public SkNVRefCnt<DistanceAdjustTable> {
DistanceAdjustTable() { this->buildDistanceAdjustTable(); }
~DistanceAdjustTable() { delete[] fTable; }
const SkScalar& operator[] (int i) const {
return fTable[i];
}
private:
void buildDistanceAdjustTable();
SkScalar* fTable;
};
GrBatchTextStrike* fCurrStrike;
GrTextBlobCache* fCache;
SkAutoTUnref<const DistanceAdjustTable> fDistanceAdjustTable;
friend class GrTextBlobCache;
friend class GrAtlasTextBatch;
SkAutoTUnref<const GrDistanceFieldAdjustTable> fDistanceAdjustTable;
#ifdef GR_TEST_UTILS
DRAW_BATCH_TEST_FRIEND(TextBlobBatch);

93
src/gpu/GrDistanceFieldAdjustTable.cpp Normal file
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@ -0,0 +1,93 @@
/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "GrDistanceFieldAdjustTable.h"
#include "SkScalerContext.h"
SkDEBUGCODE(static const int kExpectedDistanceAdjustTableSize = 8;)
void GrDistanceFieldAdjustTable::buildDistanceAdjustTable() {
// This is used for an approximation of the mask gamma hack, used by raster and bitmap
// text. The mask gamma hack is based off of guessing what the blend color is going to
// be, and adjusting the mask so that when run through the linear blend will
// produce the value closest to the desired result. However, in practice this means
// that the 'adjusted' mask is just increasing or decreasing the coverage of
// the mask depending on what it is thought it will blit against. For black (on
// assumed white) this means that coverages are decreased (on a curve). For white (on
// assumed black) this means that coverages are increased (on a a curve). At
// middle (perceptual) gray (which could be blit against anything) the coverages
// remain the same.
//
// The idea here is that instead of determining the initial (real) coverage and
// then adjusting that coverage, we determine an adjusted coverage directly by
// essentially manipulating the geometry (in this case, the distance to the glyph
// edge). So for black (on assumed white) this thins a bit; for white (on
// assumed black) this fake bolds the geometry a bit.
//
// The distance adjustment is calculated by determining the actual coverage value which
// when fed into in the mask gamma table gives us an 'adjusted coverage' value of 0.5. This
// actual coverage value (assuming it's between 0 and 1) corresponds to a distance from the
// actual edge. So by subtracting this distance adjustment and computing without the
// the coverage adjustment we should get 0.5 coverage at the same point.
//
// This has several implications:
// For non-gray lcd smoothed text, each subpixel essentially is using a
// slightly different geometry.
//
// For black (on assumed white) this may not cover some pixels which were
// previously covered; however those pixels would have been only slightly
// covered and that slight coverage would have been decreased anyway. Also, some pixels
// which were previously fully covered may no longer be fully covered.
//
// For white (on assumed black) this may cover some pixels which weren't
// previously covered at all.
int width, height;
size_t size;
#ifdef SK_GAMMA_CONTRAST
SkScalar contrast = SK_GAMMA_CONTRAST;
#else
SkScalar contrast = 0.5f;
#endif
SkScalar paintGamma = SK_GAMMA_EXPONENT;
SkScalar deviceGamma = SK_GAMMA_EXPONENT;
size = SkScalerContext::GetGammaLUTSize(contrast, paintGamma, deviceGamma,
&width, &height);
SkASSERT(kExpectedDistanceAdjustTableSize == height);
fTable = new SkScalar[height];
SkAutoTArray<uint8_t> data((int)size);
SkScalerContext::GetGammaLUTData(contrast, paintGamma, deviceGamma, data.get());
// find the inverse points where we cross 0.5
// binsearch might be better, but we only need to do this once on creation
for (int row = 0; row < height; ++row) {
uint8_t* rowPtr = data.get() + row*width;
for (int col = 0; col < width - 1; ++col) {
if (rowPtr[col] <= 127 && rowPtr[col + 1] >= 128) {
// compute point where a mask value will give us a result of 0.5
float interp = (127.5f - rowPtr[col]) / (rowPtr[col + 1] - rowPtr[col]);
float borderAlpha = (col + interp) / 255.f;
// compute t value for that alpha
// this is an approximate inverse for smoothstep()
float t = borderAlpha*(borderAlpha*(4.0f*borderAlpha - 6.0f) + 5.0f) / 3.0f;
// compute distance which gives us that t value
const float kDistanceFieldAAFactor = 0.65f; // should match SK_DistanceFieldAAFactor
float d = 2.0f*kDistanceFieldAAFactor*t - kDistanceFieldAAFactor;
fTable[row] = d;
break;
}
}
}
}

31
src/gpu/GrDistanceFieldAdjustTable.h Normal file
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@ -0,0 +1,31 @@
/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef GrDistanceFieldAdjustTable_DEFINED
#define GrDistanceFieldAdjustTable_DEFINED
#include "SkRefCnt.h"
#include "SkScalar.h"
// Distance field text needs this table to compute a value for use in the fragment shader.
// Because the GrAtlasTextContext can go out of scope before the final flush, this needs to be
// refcnted and malloced
struct GrDistanceFieldAdjustTable : public SkNVRefCnt<GrDistanceFieldAdjustTable> {
GrDistanceFieldAdjustTable() { this->buildDistanceAdjustTable(); }
~GrDistanceFieldAdjustTable() { delete[] fTable; }
const SkScalar& operator[] (int i) const {
return fTable[i];
}
private:
void buildDistanceAdjustTable();
SkScalar* fTable;
};
#endif

13
src/gpu/batches/GrAtlasTextBatch.h
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@ -11,6 +11,7 @@
#include "batches/GrVertexBatch.h"
#include "GrAtlasTextContext.h"
#include "GrDistanceFieldAdjustTable.h"
class GrAtlasTextBatch : public GrVertexBatch {
public:
@ -19,7 +20,6 @@ public:
static const int kVerticesPerGlyph = GrAtlasTextBlob::kVerticesPerGlyph;
static const int kIndicesPerGlyph = 6;
typedef GrAtlasTextContext::DistanceAdjustTable DistanceAdjustTable;
typedef GrAtlasTextBlob Blob;
typedef Blob::Run Run;
typedef Run::SubRunInfo TextInfo;
@ -56,10 +56,11 @@ public:
return batch;
}
static GrAtlasTextBatch* CreateDistanceField(int glyphCount, GrBatchFontCache* fontCache,
const DistanceAdjustTable* distanceAdjustTable,
SkColor filteredColor, bool isLCD,
bool useBGR) {
static GrAtlasTextBatch* CreateDistanceField(
int glyphCount, GrBatchFontCache* fontCache,
const GrDistanceFieldAdjustTable* distanceAdjustTable,
SkColor filteredColor, bool isLCD,
bool useBGR) {
GrAtlasTextBatch* batch = new GrAtlasTextBatch;
batch->fFontCache = fontCache;
@ -196,7 +197,7 @@ private:
GrBatchFontCache* fFontCache;
// Distance field properties
SkAutoTUnref<const DistanceAdjustTable> fDistanceAdjustTable;
SkAutoTUnref<const GrDistanceFieldAdjustTable> fDistanceAdjustTable;
SkColor fFilteredColor;
typedef GrVertexBatch INHERITED;