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Reland "Use a table for dither effect rather than math."

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This is a reland of 0de475e29e

Old code restored behind a build flag pending web_test rebaseline.

Original change's description:
> Use a table for dither effect rather than math.
>
> We used to use integer math on sk_FragCoord, when supported, and a
> fallback using floating point (on a 4x4 rather than 8x8 grid). Now we
> precompute a 8x8 table in a texture because it was shown to be
> significantly faster on several devices. Test was done with the following
> running in viewer with the stats layer enabled and looking at total
> frame time:
>  SkRandom r;
>  for (int i = 0; i < N; ++i) {
>      SkColor c[2] = {r.nextU(), c[1] = r.nextU()};
>      SkPoint pts[2] = {{r.nextRangeScalar(0, 500), r.nextRangeScalar(0, 500)},
>                        {r.nextRangeScalar(0, 500), r.nextRangeScalar(0, 500)}};
>      SkPaint p;
>      p.setDither(true);
>      p.setShader(SkGradientShader::MakeLinear(pts, c, nullptr, 2, SkTileMode::kRepeat));
>      canvas->drawPaint(p);
>  }
>
> Device            GPU             N      no dither    int math dither   table dither
> Linux desktop     QuadroP1000     5000   304ms        400ms (1.31x)     383ms (1.26x)
> TecnoSpark3Pro    PowerVRGE8320   200    299ms        820ms (2.74x)     592ms (1.98x)
> Pixel 4           Adreno640       500    110ms        221ms (2.01x)     214ms (1.95x)
> Galaxy S20 FE     Mali-G77 MP11   600    165ms        360ms (2.18x)     260ms (1.58x)
>
>
> Bug: b/195281495
> Change-Id: I200a2be8e450ab66f7c8ae340a5c83ec6780db09
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437239
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>

Bug: b/195281495
Change-Id: Ia52d24aa731281b161865b08954f9eeaca0033eb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437677
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
This commit is contained in:
Brian Salomon 2021-08-09 10:35:55 -04:00 committed by SkCQ
parent e1d0040c54
commit e1428b08df
1 changed files with 81 additions and 2 deletions
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83
src/gpu/SkGr.cpp
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@ -44,6 +44,7 @@
#include "src/gpu/effects/GrBlendFragmentProcessor.h"
#include "src/gpu/effects/GrPorterDuffXferProcessor.h"
#include "src/gpu/effects/GrSkSLFP.h"
#include "src/gpu/effects/GrTextureEffect.h"
#include "src/image/SkImage_Base.h"
#include "src/shaders/SkShaderBase.h"
@ -324,8 +325,37 @@ static inline float dither_range_for_config(GrColorType dstColorType) {
SkUNREACHABLE;
}
#if !defined(SK_DISABLE_GPU_TABLE_DITHER)
static SkBitmap make_dither_lut() {
static constexpr struct DitherTable {
constexpr DitherTable() : data() {
for (int x = 0; x < 8; ++x) {
for (int y = 0; y < 8; ++y) {
// The computation of 'm' and 'value' is lifted from CPU backend.
unsigned int m = (y & 1) << 5 | (x & 1) << 4 |
(y & 2) << 2 | (x & 2) << 1 |
(y & 4) >> 1 | (x & 4) >> 2;
float value = float(m) * 1.0 / 64.0 - 63.0 / 128.0;
// Bias by 0.5 to be in 0..1, mul by 255 and round to nearest int to make byte.
data[y * 8 + x] = (uint8_t)((value + 0.5) * 255.f + 0.5f);
}
}
}
uint8_t data[64];
} gTable;
SkBitmap bmp;
bmp.setInfo(SkImageInfo::MakeA8(8, 8));
bmp.setPixels(const_cast<uint8_t*>(gTable.data));
bmp.setImmutable();
return bmp;
}
#endif
static std::unique_ptr<GrFragmentProcessor> make_dither_effect(
std::unique_ptr<GrFragmentProcessor> inputFP, float range, const GrCaps* caps) {
GrRecordingContext* rContext,
std::unique_ptr<GrFragmentProcessor> inputFP,
float range,
const GrCaps* caps) {
if (range == 0 || inputFP == nullptr) {
return inputFP;
}
@ -334,6 +364,54 @@ static std::unique_ptr<GrFragmentProcessor> make_dither_effect(
return inputFP;
}
#if !defined(SK_DISABLE_GPU_TABLE_DITHER)
// We used to use integer math on sk_FragCoord, when supported, and a fallback using floating
// point (on a 4x4 rather than 8x8 grid). Now we precompute a 8x8 table in a texture because
// it was shown to be significantly faster on several devices. Test was done with the following
// running in viewer with the stats layer enabled and looking at total frame time:
// SkRandom r;
// for (int i = 0; i < N; ++i) {
// SkColor c[2] = {r.nextU(), c[1] = r.nextU()};
// SkPoint pts[2] = {{r.nextRangeScalar(0, 500), r.nextRangeScalar(0, 500)},
// {r.nextRangeScalar(0, 500), r.nextRangeScalar(0, 500)}};
// SkPaint p;
// p.setDither(true);
// p.setShader(SkGradientShader::MakeLinear(pts, c, nullptr, 2, SkTileMode::kRepeat));
// canvas->drawPaint(p);
// }
// Device GPU N no dither int math dither table dither
// Linux desktop QuadroP1000 5000 304ms 400ms (1.31x) 383ms (1.26x)
// TecnoSpark3Pro PowerVRGE8320 200 299ms 820ms (2.74x) 592ms (1.98x)
// Pixel 4 Adreno640 500 110ms 221ms (2.01x) 214ms (1.95x)
// Galaxy S20 FE Mali-G77 MP11 600 165ms 360ms (2.18x) 260ms (1.58x)
static const SkBitmap gLUT = make_dither_lut();
auto [tex, ct] = GrMakeCachedBitmapProxyView(rContext, gLUT, GrMipmapped::kNo);
if (!tex) {
return inputFP;
}
SkASSERT(ct == GrColorType::kAlpha_8);
GrSamplerState sampler(GrSamplerState::WrapMode::kRepeat, SkFilterMode::kNearest);
auto te = GrTextureEffect::Make(
std::move(tex), kPremul_SkAlphaType, SkMatrix::I(), sampler, *caps);
static auto effect = SkMakeRuntimeEffect(SkRuntimeEffect::MakeForShader, R"(
uniform half range;
uniform shader table;
half4 main(float2 xy, half4 color) {
half value = sample(table, sk_FragCoord.xy).a - 0.5; // undo the bias in the table
// For each color channel, add the random offset to the channel value and then clamp
// between 0 and alpha to keep the color premultiplied.
return half4(clamp(color.rgb + value * range, 0.0, color.a), color.a);
}
)", SkRuntimeEffectPriv::ES3Options());
return GrSkSLFP::Make(effect,
"Dither",
std::move(inputFP),
GrSkSLFP::OptFlags::kPreservesOpaqueInput,
"range",
range,
"table",
std::move(te));
#else
if (caps->shaderCaps()->integerSupport()) {
// This ordered-dither code is lifted from the cpu backend.
static auto effect = SkMakeRuntimeEffect(SkRuntimeEffect::MakeForShader, R"(
@ -387,6 +465,7 @@ static std::unique_ptr<GrFragmentProcessor> make_dither_effect(
GrSkSLFP::OptFlags::kPreservesOpaqueInput,
"range", range);
}
#endif
}
#endif
@ -504,7 +583,7 @@ static inline bool skpaint_to_grpaint_impl(GrRecordingContext* context,
if (SkPaintPriv::ShouldDither(skPaint, GrColorTypeToSkColorType(ct)) && paintFP != nullptr) {
float ditherRange = dither_range_for_config(ct);
paintFP = make_dither_effect(
std::move(paintFP), ditherRange, context->priv().caps());
context, std::move(paintFP), ditherRange, context->priv().caps());
}
#endif