Interpolate vertical linear gradients for improved quality.
Consolidate interpolation functions, add new faster more accurate dithering
interpolator.
git-svn-id: http://skia.googlecode.com/svn/trunk@3072 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkGradientShader.cpp b/src/effects/SkGradientShader.cpp
index 729d39b..8c6bcfb 100644
--- a/src/effects/SkGradientShader.cpp
+++ b/src/effects/SkGradientShader.cpp
@@ -119,28 +119,41 @@
virtual bool isOpaque() const SK_OVERRIDE;
enum {
- kCache16Bits = 8, // seems like enough for visual accuracy
- kCache16Count = 1 << kCache16Bits,
- kCache16Mask = kCache16Count - 1,
+ /// Seems like enough for visual accuracy. TODO: if pos[] deserves
+ /// it, use a larger cache.
+ kCache16Bits = 8,
+ kGradient16Length = (1 << kCache16Bits),
+ /// Each cache gets 1 extra entry at the end so we don't have to
+ /// test for end-of-cache in lerps. This is also the value used
+ /// to stride *writes* into the dither cache; it must not be zero.
+ /// Total space for a cache is 2x kCache16Count entries: one
+ /// regular cache, one for dithering.
+ kCache16Count = kGradient16Length + 1,
kCache16Shift = 16 - kCache16Bits,
kSqrt16Shift = 8 - kCache16Bits,
- kCache32Bits = 8, // pretty much should always be 8
- kCache32Count = 1 << kCache32Bits,
- kCache32Mask = kCache32Count - 1,
+ /// Seems like enough for visual accuracy. TODO: if pos[] deserves
+ /// it, use a larger cache.
+ kCache32Bits = 8,
+ kGradient32Length = (1 << kCache32Bits),
+ /// Each cache gets 1 extra entry at the end so we don't have to
+ /// test for end-of-cache in lerps. This is also the value used
+ /// to stride *writes* into the dither cache; it must not be zero.
+ /// Total space for a cache is 2x kCache32Count entries: one
+ /// regular cache, one for dithering.
+ kCache32Count = kGradient32Length + 1,
kCache32Shift = 16 - kCache32Bits,
kSqrt32Shift = 8 - kCache32Bits,
- /** ToggleMasks are used in dithering to switch between the two
- halves of the gradient cache; they should be equal to the size
- of a half-cache.
- */
+ /// This value is used to *read* the dither cache; it may be 0
+ /// if dithering is disabled.
#ifdef USE_DITHER_32BIT_GRADIENT
- kToggleMask32 = kCache32Count,
+ kDitherStride32 = kCache32Count,
#else
- kToggleMask32 = 0,
+ kDitherStride32 = 0,
#endif
- kToggleMask16 = kCache16Count
+ kDitherStride16 = kCache16Count,
+ kLerpRemainderMask32 = (1 << (16 - kCache32Bits)) - 1
};
@@ -557,10 +570,11 @@
do {
cache[0] = SkPremultiplyARGBInline(a >> 16, r >> 16, g >> 16, b >> 16);
- cache[kCache32Count] = SkPremultiplyARGBInline(dither_ceil_fixed_to_8(a),
- dither_fixed_to_8(r),
- dither_fixed_to_8(g),
- dither_fixed_to_8(b));
+ cache[kCache32Count] =
+ SkPremultiplyARGBInline(dither_ceil_fixed_to_8(a),
+ dither_fixed_to_8(r),
+ dither_fixed_to_8(g),
+ dither_fixed_to_8(b));
cache += 1;
a += da;
r += dr;
@@ -586,6 +600,14 @@
return 0;
}
+/** We duplicate the last value in each half of the cache so that
+ interpolation doesn't have to special-case being at the last point.
+*/
+static void complete_16bit_cache(uint16_t* cache, int stride) {
+ cache[stride - 1] = cache[stride - 2];
+ cache[2 * stride - 1] = cache[2 * stride - 2];
+}
+
const uint16_t* Gradient_Shader::getCache16() const {
if (fCache16 == NULL) {
// double the count for dither entries
@@ -597,7 +619,8 @@
}
fCache16 = fCache16Storage;
if (fColorCount == 2) {
- Build16bitCache(fCache16, fOrigColors[0], fOrigColors[1], kCache16Count);
+ Build16bitCache(fCache16, fOrigColors[0], fOrigColors[1],
+ kGradient16Length);
} else {
Rec* rec = fRecs;
int prevIndex = 0;
@@ -609,7 +632,8 @@
Build16bitCache(fCache16 + prevIndex, fOrigColors[i-1], fOrigColors[i], nextIndex - prevIndex + 1);
prevIndex = nextIndex;
}
- SkASSERT(prevIndex == kCache16Count - 1);
+ // one extra space left over at the end for complete_16bit_cache()
+ SkASSERT(prevIndex == kGradient16Length - 1);
}
if (fMapper) {
@@ -617,7 +641,7 @@
uint16_t* linear = fCache16; // just computed linear data
uint16_t* mapped = fCache16Storage; // storage for mapped data
SkUnitMapper* map = fMapper;
- for (int i = 0; i < kCache16Count; i++) {
+ for (int i = 0; i < kGradient16Length; i++) {
int index = map->mapUnit16(bitsTo16(i, kCache16Bits)) >> kCache16Shift;
mapped[i] = linear[index];
mapped[i + kCache16Count] = linear[index + kCache16Count];
@@ -625,10 +649,19 @@
sk_free(fCache16);
fCache16 = fCache16Storage;
}
+ complete_16bit_cache(fCache16, kCache16Count);
}
return fCache16;
}
+/** We duplicate the last value in each half of the cache so that
+ interpolation doesn't have to special-case being at the last point.
+*/
+static void complete_32bit_cache(SkPMColor* cache, int stride) {
+ cache[stride - 1] = cache[stride - 2];
+ cache[2 * stride - 1] = cache[2 * stride - 2];
+}
+
const SkPMColor* Gradient_Shader::getCache32() const {
if (fCache32 == NULL) {
// double the count for dither entries
@@ -642,13 +675,13 @@
fCache32 = (SkPMColor*)fCache32PixelRef->getAddr();
if (fColorCount == 2) {
Build32bitCache(fCache32, fOrigColors[0], fOrigColors[1],
- kCache32Count, fCacheAlpha);
+ kGradient32Length, fCacheAlpha);
} else {
Rec* rec = fRecs;
int prevIndex = 0;
for (int i = 1; i < fColorCount; i++) {
int nextIndex = SkFixedToFFFF(rec[i].fPos) >> kCache32Shift;
- SkASSERT(nextIndex < kCache32Count);
+ SkASSERT(nextIndex < kGradient32Length);
if (nextIndex > prevIndex)
Build32bitCache(fCache32 + prevIndex, fOrigColors[i-1],
@@ -656,7 +689,7 @@
nextIndex - prevIndex + 1, fCacheAlpha);
prevIndex = nextIndex;
}
- SkASSERT(prevIndex == kCache32Count - 1);
+ SkASSERT(prevIndex == kGradient32Length - 1);
}
if (fMapper) {
@@ -665,7 +698,7 @@
SkPMColor* linear = fCache32; // just computed linear data
SkPMColor* mapped = (SkPMColor*)newPR->getAddr(); // storage for mapped data
SkUnitMapper* map = fMapper;
- for (int i = 0; i < kCache32Count; i++) {
+ for (int i = 0; i < kGradient32Length; i++) {
int index = map->mapUnit16((i << 8) | i) >> 8;
mapped[i] = linear[index];
mapped[i + kCache32Count] = linear[index + kCache32Count];
@@ -674,6 +707,7 @@
fCache32PixelRef = newPR;
fCache32 = (SkPMColor*)newPR->getAddr();
}
+ complete_32bit_cache(fCache32, kCache32Count);
}
return fCache32;
}
@@ -695,7 +729,7 @@
if (fMapper) {
// force our cahce32pixelref to be built
(void)this->getCache32();
- bitmap->setConfig(SkBitmap::kARGB_8888_Config, kCache32Count, 1);
+ bitmap->setConfig(SkBitmap::kARGB_8888_Config, kGradient32Length, 1);
bitmap->setPixelRef(fCache32PixelRef);
return;
}
@@ -735,7 +769,9 @@
if (!gCache->find(storage.get(), size, bitmap)) {
// force our cahce32pixelref to be built
(void)this->getCache32();
- bitmap->setConfig(SkBitmap::kARGB_8888_Config, kCache32Count, 1);
+ // Only expose the linear section of the cache; don't let the caller
+ // know about the padding at the end to make interpolation faster.
+ bitmap->setConfig(SkBitmap::kARGB_8888_Config, kGradient32Length, 1);
bitmap->setPixelRef(fCache32PixelRef);
gCache->add(storage.get(), size, *bitmap);
@@ -851,7 +887,7 @@
SkASSERT(fi <= 0xFF); \
fx += dx; \
*dstC++ = cache[toggle + fi]; \
- toggle ^= Gradient_Shader::kToggleMask32; \
+ toggle ^= Gradient_Shader::kDitherStride32; \
} while (0)
namespace {
@@ -860,15 +896,28 @@
SkPMColor* dstC, const SkPMColor* cache,
int toggle, int count);
-void shadeSpan_linear_vertical(TileProc proc, SkFixed dx, SkFixed fx,
- SkPMColor* SK_RESTRICT dstC,
- const SkPMColor* SK_RESTRICT cache,
- int toggle, int count) {
- // we're a vertical gradient, so no change in a span
- unsigned fi = proc(fx) >> Gradient_Shader::kCache32Shift;
- sk_memset32_dither(dstC, cache[toggle + fi],
- cache[(toggle ^ Gradient_Shader::kToggleMask32) + fi], count);
-
+// lerp is unnecessary if there are no sharp discontinuities in the
+// gradient - which must be true if there are only 2 colors - but for
+// vertical gradients it's so cheap we do it anyway.
+void shadeSpan_linear_vertical_lerp(TileProc proc, SkFixed dx, SkFixed fx,
+ SkPMColor* SK_RESTRICT dstC,
+ const SkPMColor* SK_RESTRICT cache,
+ int toggle, int count) {
+ // We're a vertical gradient, so no change in a span.
+ // If colors change sharply across the gradient, dithering is
+ // insufficient (it subsamples the color space) and we need to lerp.
+ unsigned fullIndex = proc(fx);
+ unsigned fi = fullIndex >> (16 - Gradient_Shader::kCache32Bits);
+ unsigned remainder = fullIndex & Gradient_Shader::kLerpRemainderMask32;
+ SkPMColor lerp =
+ SkFastFourByteInterp(
+ cache[toggle + fi + 1],
+ cache[toggle + fi], remainder);
+ SkPMColor dlerp =
+ SkFastFourByteInterp(
+ cache[(toggle ^ Gradient_Shader::kDitherStride32) + fi + 1],
+ cache[(toggle ^ Gradient_Shader::kDitherStride32) + fi], remainder);
+ sk_memset32_dither(dstC, lerp, dlerp, count);
}
void shadeSpan_linear_clamp(TileProc proc, SkFixed dx, SkFixed fx,
@@ -876,12 +925,12 @@
const SkPMColor* SK_RESTRICT cache,
int toggle, int count) {
SkClampRange range;
- range.init(fx, dx, count, 0, 0xFF);
+ range.init(fx, dx, count, 0, Gradient_Shader::kGradient32Length);
if ((count = range.fCount0) > 0) {
sk_memset32_dither(dstC,
cache[toggle + range.fV0],
- cache[(toggle ^ Gradient_Shader::kToggleMask32) + range.fV0],
+ cache[(toggle ^ Gradient_Shader::kDitherStride32) + range.fV0],
count);
dstC += count;
}
@@ -903,13 +952,11 @@
if ((count = range.fCount2) > 0) {
sk_memset32_dither(dstC,
cache[toggle + range.fV1],
- cache[(toggle ^ Gradient_Shader::kToggleMask32) + range.fV1],
+ cache[(toggle ^ Gradient_Shader::kDitherStride32) + range.fV1],
count);
}
}
-// TODO: we could merge mirror and repeat if we passed in a pointer to the
-// *_8bits proc, but that'd lose inlining, which might be significant here.
void shadeSpan_linear_mirror(TileProc proc, SkFixed dx, SkFixed fx,
SkPMColor* SK_RESTRICT dstC,
const SkPMColor* SK_RESTRICT cache,
@@ -919,7 +966,7 @@
SkASSERT(fi <= 0xFF);
fx += dx;
*dstC++ = cache[toggle + fi];
- toggle ^= Gradient_Shader::kToggleMask32;
+ toggle ^= Gradient_Shader::kDitherStride32;
} while (--count != 0);
}
@@ -932,9 +979,10 @@
SkASSERT(fi <= 0xFF);
fx += dx;
*dstC++ = cache[toggle + fi];
- toggle ^= Gradient_Shader::kToggleMask32;
+ toggle ^= Gradient_Shader::kDitherStride32;
} while (--count != 0);
}
+
}
void Linear_Gradient::shadeSpan(int x, int y, SkPMColor* SK_RESTRICT dstC,
@@ -946,7 +994,7 @@
TileProc proc = fTileProc;
const SkPMColor* SK_RESTRICT cache = this->getCache32();
#ifdef USE_DITHER_32BIT_GRADIENT
- int toggle = ((x ^ y) & 1) << kCache32Bits;
+ int toggle = ((x ^ y) & 1) * kDitherStride32;
#else
int toggle = 0;
#endif
@@ -967,7 +1015,7 @@
LinearShadeProc shadeProc = shadeSpan_linear_repeat;
if (SkFixedNearlyZero(dx)) {
- shadeProc = shadeSpan_linear_vertical;
+ shadeProc = shadeSpan_linear_vertical_lerp;
} else if (proc == clamp_tileproc) {
shadeProc = shadeSpan_linear_clamp;
} else if (proc == mirror_tileproc) {
@@ -984,7 +1032,7 @@
unsigned fi = proc(SkScalarToFixed(srcPt.fX));
SkASSERT(fi <= 0xFFFF);
*dstC++ = cache[toggle + (fi >> kCache32Shift)];
- toggle ^= Gradient_Shader::kToggleMask32;
+ toggle ^= Gradient_Shader::kDitherStride32;
dstX += SK_Scalar1;
} while (--count != 0);
}
@@ -998,7 +1046,7 @@
this->commonAsABitmap(bitmap);
}
if (matrix) {
- matrix->setScale(SkIntToScalar(kCache32Count), SK_Scalar1);
+ matrix->setScale(SkIntToScalar(kGradient32Length), SK_Scalar1);
matrix->preConcat(fPtsToUnit);
}
if (xy) {
@@ -1035,10 +1083,10 @@
#define NO_CHECK_ITER_16 \
do { \
unsigned fi = fx >> Gradient_Shader::kCache16Shift; \
- SkASSERT(fi <= Gradient_Shader::kCache16Mask); \
+ SkASSERT(fi < Gradient_Shader::kCache16Count); \
fx += dx; \
*dstC++ = cache[toggle + fi]; \
- toggle ^= Gradient_Shader::kToggleMask16; \
+ toggle ^= Gradient_Shader::kDitherStride16; \
} while (0)
namespace {
@@ -1053,9 +1101,9 @@
int toggle, int count) {
// we're a vertical gradient, so no change in a span
unsigned fi = proc(fx) >> Gradient_Shader::kCache16Shift;
- SkASSERT(fi <= Gradient_Shader::kCache16Mask);
+ SkASSERT(fi < Gradient_Shader::kCache16Count);
dither_memset16(dstC, cache[toggle + fi],
- cache[(toggle ^ Gradient_Shader::kToggleMask16) + fi], count);
+ cache[(toggle ^ Gradient_Shader::kDitherStride16) + fi], count);
}
@@ -1064,12 +1112,12 @@
const uint16_t* SK_RESTRICT cache,
int toggle, int count) {
SkClampRange range;
- range.init(fx, dx, count, 0, Gradient_Shader::kCache16Mask);
+ range.init(fx, dx, count, 0, Gradient_Shader::kGradient16Length);
if ((count = range.fCount0) > 0) {
dither_memset16(dstC,
cache[toggle + range.fV0],
- cache[(toggle ^ Gradient_Shader::kToggleMask16) + range.fV0],
+ cache[(toggle ^ Gradient_Shader::kDitherStride16) + range.fV0],
count);
dstC += count;
}
@@ -1091,7 +1139,7 @@
if ((count = range.fCount2) > 0) {
dither_memset16(dstC,
cache[toggle + range.fV1],
- cache[(toggle ^ Gradient_Shader::kToggleMask16) + range.fV1],
+ cache[(toggle ^ Gradient_Shader::kDitherStride16) + range.fV1],
count);
}
}
@@ -1103,10 +1151,10 @@
do {
unsigned fi = mirror_bits(fx >> Gradient_Shader::kCache16Shift,
Gradient_Shader::kCache16Bits);
- SkASSERT(fi <= Gradient_Shader::kCache16Mask);
+ SkASSERT(fi < Gradient_Shader::kCache16Count);
fx += dx;
*dstC++ = cache[toggle + fi];
- toggle ^= Gradient_Shader::kToggleMask16;
+ toggle ^= Gradient_Shader::kDitherStride16;
} while (--count != 0);
}
@@ -1118,10 +1166,10 @@
do {
unsigned fi = repeat_bits(fx >> Gradient_Shader::kCache16Shift,
Gradient_Shader::kCache16Bits);
- SkASSERT(fi <= Gradient_Shader::kCache16Mask);
+ SkASSERT(fi < Gradient_Shader::kCache16Count);
fx += dx;
*dstC++ = cache[toggle + fi];
- toggle ^= Gradient_Shader::kToggleMask16;
+ toggle ^= Gradient_Shader::kDitherStride16;
} while (--count != 0);
}
}
@@ -1134,7 +1182,7 @@
SkMatrix::MapXYProc dstProc = fDstToIndexProc;
TileProc proc = fTileProc;
const uint16_t* SK_RESTRICT cache = this->getCache16();
- int toggle = ((x ^ y) & 1) << kCache16Bits;
+ int toggle = ((x ^ y) & 1) * kDitherStride16;
if (fDstToIndexClass != kPerspective_MatrixClass) {
dstProc(fDstToIndex, SkIntToScalar(x) + SK_ScalarHalf,
@@ -1171,7 +1219,7 @@
int index = fi >> kCache16Shift;
*dstC++ = cache[toggle + index];
- toggle ^= Gradient_Shader::kToggleMask16;
+ toggle ^= Gradient_Shader::kDitherStride16;
dstX += SK_Scalar1;
} while (--count != 0);
@@ -1263,7 +1311,7 @@
fx += dx;
*dstC++ = cache[toggle +
(sqrt_table[fi] >> Gradient_Shader::kSqrt16Shift)];
- toggle ^= Gradient_Shader::kToggleMask16;
+ toggle ^= Gradient_Shader::kDitherStride16;
} while (--count != 0);
} else {
do {
@@ -1275,7 +1323,7 @@
fy += dy;
*dstC++ = cache[toggle +
(sqrt_table[fi] >> Gradient_Shader::kSqrt16Shift)];
- toggle ^= Gradient_Shader::kToggleMask16;
+ toggle ^= Gradient_Shader::kDitherStride16;
} while (--count != 0);
}
}
@@ -1298,7 +1346,7 @@
unsigned fi = mirror_tileproc(dist);
SkASSERT(fi <= 0xFFFF);
*dstC++ = cache[toggle + (fi >> Gradient_Shader::kCache16Shift)];
- toggle ^= Gradient_Shader::kToggleMask16;
+ toggle ^= Gradient_Shader::kDitherStride16;
sfx += sdx;
sfy += sdy;
} while (--count != 0);
@@ -1319,7 +1367,7 @@
fx += dx;
fy += dy;
*dstC++ = cache[toggle + (fi >> Gradient_Shader::kCache16Shift)];
- toggle ^= Gradient_Shader::kToggleMask16;
+ toggle ^= Gradient_Shader::kDitherStride16;
} while (--count != 0);
}
@@ -1350,7 +1398,7 @@
SkMatrix::MapXYProc dstProc = fDstToIndexProc;
TileProc proc = fTileProc;
const uint16_t* SK_RESTRICT cache = this->getCache16();
- int toggle = ((x ^ y) & 1) << kCache16Bits;
+ int toggle = ((x ^ y) & 1) * kDitherStride16;
if (fDstToIndexClass != kPerspective_MatrixClass) {
dstProc(fDstToIndex, SkIntToScalar(x) + SK_ScalarHalf,
@@ -1389,7 +1437,7 @@
int index = fi >> (16 - kCache16Bits);
*dstC++ = cache[toggle + index];
- toggle ^= (1 << kCache16Bits);
+ toggle ^= kDitherStride16;
dstX += SK_Scalar1;
} while (--count != 0);
@@ -1405,8 +1453,8 @@
this->commonAsABitmap(bitmap);
}
if (matrix) {
- matrix->setScale(SkIntToScalar(kCache32Count),
- SkIntToScalar(kCache32Count));
+ matrix->setScale(SkIntToScalar(kGradient32Length),
+ SkIntToScalar(kGradient32Length));
matrix->preConcat(fPtsToUnit);
}
if (xy) {
@@ -1506,7 +1554,7 @@
SkFixed fy = SkScalarToFixed(sfy) >> 1;
SkFixed dy = SkScalarToFixed(sdy) >> 1;
if ((count > 4) && radial_completely_pinned(fx, dx, fy, dy)) {
- sk_memset32(dstC, cache[Gradient_Shader::kCache32Count - 1], count);
+ sk_memset32(dstC, cache[Gradient_Shader::kGradient32Length], count);
} else if ((count > 4) &&
no_need_for_radial_pin(fx, dx, fy, dy, count)) {
unsigned fi;
@@ -2338,7 +2386,7 @@
SkMatrix::MapXYProc proc = fDstToIndexProc;
const SkMatrix& matrix = fDstToIndex;
const uint16_t* SK_RESTRICT cache = this->getCache16();
- int toggle = ((x ^ y) & 1) << kCache16Bits;
+ int toggle = ((x ^ y) & 1) * kDitherStride16;
SkPoint srcPt;
if (fDstToIndexClass != kPerspective_MatrixClass) {
@@ -2362,7 +2410,7 @@
for (; count > 0; --count) {
int index = SkATan2_255(fy, fx) >> (8 - kCache16Bits);
*dstC++ = cache[toggle + index];
- toggle ^= (1 << kCache16Bits);
+ toggle ^= kDitherStride16;
fx += dx;
fy += dy;
}
@@ -2374,7 +2422,7 @@
int index = SkATan2_255(srcPt.fY, srcPt.fX);
index >>= (8 - kCache16Bits);
*dstC++ = cache[toggle + index];
- toggle ^= (1 << kCache16Bits);
+ toggle ^= kDitherStride16;
}
}
}