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skia / skia / refs/heads/main / . / src / core / SkBlurEngine.cpp
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/*
* Copyright 2024 Google LLC
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "src/core/SkBlurEngine.h"
#include "include/core/SkAlphaType.h"
#include "include/core/SkBitmap.h"
#include "include/core/SkBlendMode.h"
#include "include/core/SkClipOp.h"
#include "include/core/SkColor.h"
#include "include/core/SkColorSpace.h" // IWYU pragma: keep
#include "include/core/SkColorType.h"
#include "include/core/SkImageInfo.h"
#include "include/core/SkM44.h"
#include "include/core/SkMatrix.h"
#include "include/core/SkPaint.h"
#include "include/core/SkPoint.h"
#include "include/core/SkRect.h"
#include "include/core/SkSamplingOptions.h"
#include "include/core/SkScalar.h"
#include "include/core/SkSurfaceProps.h"
#include "include/core/SkTileMode.h"
#include "include/effects/SkRuntimeEffect.h"
#include "include/private/base/SkAssert.h"
#include "include/private/base/SkFeatures.h"
#include "include/private/base/SkMalloc.h"
#include "include/private/base/SkMath.h"
#include "include/private/base/SkTo.h"
#include "src/base/SkArenaAlloc.h"
#include "src/base/SkVx.h"
#include "src/core/SkBitmapDevice.h"
#include "src/core/SkDevice.h"
#include "src/core/SkKnownRuntimeEffects.h"
#include "src/core/SkSpecialImage.h"
#include <algorithm>
#include <array>
#include <cmath>
#include <cstdint>
#include <cstring>
#include <utility>
#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE1
#include <xmmintrin.h>
#define SK_PREFETCH(ptr) _mm_prefetch(reinterpret_cast<const char*>(ptr), _MM_HINT_T0)
#elif defined(__GNUC__)
#define SK_PREFETCH(ptr) __builtin_prefetch(ptr)
#else
#define SK_PREFETCH(ptr)
#endif
// RasterBlurEngine
// ----------------------------------------------------------------------------
namespace {
class Pass {
public:
explicit Pass(int border) : fBorder(border) {}
virtual ~Pass() = default;
// T is type of the pixel format for the color type.
template <typename T>
void blur(int srcLeft, int srcRight, int dstRight,
const T* src, int srcStride,
T* dst, int dstStride) {
this->startBlur();
auto srcStart = srcLeft - fBorder,
srcEnd = srcRight - fBorder,
dstEnd = dstRight,
srcIdx = srcStart,
dstIdx = 0;
const T* srcCursor = src;
T* dstCursor = dst;
if (dstIdx < srcIdx) {
// The destination pixels are not effected by the src pixels,
// change to zero as per the spec.
// https://drafts.fxtf.org/filter-effects/#FilterPrimitivesOverviewIntro
int commonEnd = std::min(srcIdx, dstEnd);
while (dstIdx < commonEnd) {
*dstCursor = 0;
dstCursor += dstStride;
SK_PREFETCH(dstCursor);
dstIdx++;
}
} else if (srcIdx < dstIdx) {
// The edge of the source is before the edge of the destination. Calculate the sums for
// the pixels before the start of the destination.
if (int commonEnd = std::min(dstIdx, srcEnd); srcIdx < commonEnd) {
// Preload the blur with values from src before dst is entered.
int n = commonEnd - srcIdx;
this->blurSegment(n, srcCursor, srcStride, nullptr, 0);
srcIdx += n;
srcCursor += n * srcStride;
}
if (srcIdx < dstIdx) {
// The weird case where src is out of pixels before dst is even started.
int n = dstIdx - srcIdx;
this->blurSegment(n, nullptr, 0, nullptr, 0);
srcIdx += n;
}
}
if (int commonEnd = std::min(dstEnd, srcEnd); dstIdx < commonEnd) {
// Both srcIdx and dstIdx are in sync now, and can run in a 1:1 fashion. This is the
// normal mode of operation.
SkASSERT(srcIdx == dstIdx);
int n = commonEnd - dstIdx;
this->blurSegment(n, srcCursor, srcStride, dstCursor, dstStride);
srcCursor += n * srcStride;
dstCursor += n * dstStride;
dstIdx += n;
srcIdx += n;
}
// Drain the remaining blur values into dst assuming 0's for the leading edge.
if (dstIdx < dstEnd) {
int n = dstEnd - dstIdx;
this->blurSegment(n, nullptr, 0, dstCursor, dstStride);
}
}
protected:
virtual void startBlur() = 0;
virtual void blurSegment(
int n, const void* src, int srcStride, void* dst, int dstStride) = 0;
private:
const int fBorder;
};
class PassMaker {
public:
explicit PassMaker(int window, float sigma) : fWindow{window},
fSigma{sigma} {}
virtual ~PassMaker() = default;
virtual Pass* makePass(void* buffer, SkArenaAlloc* alloc) const = 0;
virtual size_t bufferSizeBytes() const = 0;
int window() const {return fWindow;}
float sigma() const {return fSigma;}
private:
const int fWindow;
const float fSigma;
};
// T is type of the pixel format for the color type.
// This should only be used for 8bit color channels.
template <typename T>
static sk_sp<SkSpecialImage> eval_blur_passes(PassMaker* makerX, PassMaker* makerY,
SkBitmap src, const SkIRect& originalSrcBounds,
const SkIRect& originalDstBounds,
SkArenaAlloc* alloc) {
static constexpr int N = sizeof(T) / sizeof(uint8_t);
static_assert(N*sizeof(uint8_t) == sizeof(T), "N must be the the size of T in bytes.");
SkIRect srcBounds = originalSrcBounds;
SkIRect dstBounds = originalDstBounds;
if (makerX->window() > 1) {
// Inflate the dst by the window required for the Y pass so that the X pass can prepare
// it. The Y pass will be offset to only write to the original rows in dstBounds, but
// its window will access these extra rows calculated by the X pass. The SpecialImage
// factory will then subset the bitmap so it appears to match 'originalDstBounds'
// tightly. We make one slightly larger image to hold this extra data instead of two
// separate images sized exactly to each pass because the CPU blur can write in place.
dstBounds.outset(0, SkBlurEngine::SigmaToRadius(makerY->sigma()));
}
SkBitmap dst;
const SkIPoint dstOrigin = dstBounds.topLeft();
if (!dst.tryAllocPixels(src.info().makeWH(dstBounds.width(), dstBounds.height()))) {
return nullptr;
}
dst.eraseColor(SK_ColorTRANSPARENT);
auto buffer = alloc->makeBytesAlignedTo(std::max(makerX->bufferSizeBytes(),
makerY->bufferSizeBytes()),
alignof(skvx::Vec<N, uint32_t>));
// Basic Plan: The three cases to handle
// * Horizontal and Vertical - blur horizontally while copying values from the source to
// the destination. Then, do an in-place vertical blur.
// * Horizontal only - blur horizontally copying values from the source to the destination.
// * Vertical only - blur vertically copying values from the source to the destination.
// Initialize these assuming the Y-only case
int loopStart = std::max(srcBounds.left(), dstBounds.left());
int loopEnd = std::min(srcBounds.right(), dstBounds.right());
int dstYOffset = 0;
if (makerX->window() > 1) {
// First an X-only blur from src into dst, including the extra rows that will become
// input for the second Y pass, which will then be performed in place.
loopStart = std::max(srcBounds.top(), dstBounds.top());
loopEnd = std::min(srcBounds.bottom(), dstBounds.bottom());
auto srcAddr = reinterpret_cast<T*>(src.getAddr(0, loopStart - srcBounds.top()));
auto dstAddr = reinterpret_cast<T*>(dst.getAddr(0, loopStart - dstBounds.top()));
// Iterate over each row to calculate 1D blur along X.
Pass* pass = makerX->makePass(buffer, alloc);
for (int y = loopStart; y < loopEnd; ++y) {
pass->blur<T>(srcBounds.left() - dstBounds.left(),
srcBounds.right() - dstBounds.left(),
dstBounds.width(),
srcAddr, 1,
dstAddr, 1);
srcAddr += src.rowBytesAsPixels();
dstAddr += dst.rowBytesAsPixels();
}
// Set up the Y pass to blur from the full dst into the non-outset portion of dst
src = dst;
loopStart = originalDstBounds.left();
loopEnd = originalDstBounds.right();
// The new 'dst' is equal to dst.extractSubset(originalDstBounds.offset(-dstOrigin)),
// but by construction only the Y offset has an interesting value so this is a little
// more efficient.
dstYOffset = originalDstBounds.top() - dstBounds.top();
srcBounds = dstBounds;
dstBounds = originalDstBounds;
}
// Iterate over each column to calculate 1D blur along Y. This is either blurring from src
// into dst for a 1D blur; or it's blurring from dst into dst for the second pass of a 2D
// blur.
if (makerY->window() > 1) {
auto srcAddr = reinterpret_cast<T*>(src.getAddr(loopStart - srcBounds.left(), 0));
auto dstAddr = reinterpret_cast<T*>(dst.getAddr(loopStart - dstBounds.left(), dstYOffset));
Pass* pass = makerY->makePass(buffer, alloc);
for (int x = loopStart; x < loopEnd; ++x) {
pass->blur<T>(srcBounds.top() - dstBounds.top(),
srcBounds.bottom() - dstBounds.top(),
dstBounds.height(),
srcAddr, src.rowBytesAsPixels(),
dstAddr, dst.rowBytesAsPixels());
srcAddr += 1;
dstAddr += 1;
}
}
#if defined(SK_AVOID_SLOW_RASTER_PIPELINE_BLURS)
// When avoiding the shader-based algorithm, handle the box identity case.
if (makerX->window() == 1 && makerY->window() == 1) {
dst.writePixels(src.pixmap(),
srcBounds.left() - dstBounds.left(),
srcBounds.top() - dstBounds.top());
}
#endif //SK_AVOID_SLOW_RASTER_PIPELINE_BLURS
dstBounds = originalDstBounds.makeOffset(-dstOrigin); // Make relative to dst's pixels
return SkSpecialImages::MakeFromRaster(dstBounds, dst, SkSurfaceProps{});
}
// Implement a scanline processor for a true 1D Gaussian kernel.
// T is type of the pixel format for the color type.
// This should only be used for 8bit color channels.
template <typename T>
class GaussianPass final : public Pass {
public:
static constexpr int N = sizeof(T) / sizeof(uint8_t);
static_assert(N*sizeof(uint8_t) == sizeof(T), "N must be the the size of T in bytes.");
static constexpr float kMaxSigma = 2.f;
static PassMaker* MakeMaker(float sigma, SkArenaAlloc* alloc) {
if (sigma >= kMaxSigma) { return nullptr; }
class Maker : public PassMaker {
public:
explicit Maker(float sigma)
: PassMaker{2 * SkBlurEngine::SigmaToRadius(sigma) + 1, sigma} {}
Pass* makePass(void* buffer, SkArenaAlloc* alloc) const override {
return GaussianPass::Make(this->sigma(), buffer, alloc);
}
size_t bufferSizeBytes() const override {
// Data is skvx::Vec<N, float>[window] + float[window]
return this->window() * (sizeof(skvx::Vec<N, float>) + sizeof(float));
}
};
return alloc->make<Maker>(sigma);
}
static GaussianPass* Make(float sigma, void* buffers, SkArenaAlloc* alloc) {
int radius = SkBlurEngine::SigmaToRadius(sigma);
int kernelWidth = 2*radius + 1;
skvx::Vec<N, float>* srcBuffer = static_cast<skvx::Vec<N, float>*>(buffers);
float* kernelValues = reinterpret_cast<float*>(srcBuffer + kernelWidth);
SkShaderBlurAlgorithm::Compute1DBlurKernel(sigma, radius, {kernelValues, kernelWidth});
return alloc->make<GaussianPass>(radius, kernelValues, srcBuffer);
}
GaussianPass(int radius, float* kernel, skvx::Vec<N, float>* srcBuffer)
: Pass(radius),
fWindow(2 * radius + 1),
fKernel(kernel),
fSrcBuffer(srcBuffer),
fSrcBufferBase(0) {}
private:
void startBlur() override {
// Zero out the source buffer to ensure a clean state.
sk_bzero(fSrcBuffer, fWindow * sizeof(skvx::Vec<N, float>));
// Reset the circular buffer's starting position.
fSrcBufferBase = 0;
}
void blurSegment(int n, const void* src, int srcStride, void* dst, int dstStride) override {
const T* srcPtr = reinterpret_cast<const T*>(src);
T* dstPtr = reinterpret_cast<T*>(dst);
// Load the state from the last run.
int base = fSrcBufferBase;
auto convolve = [this](int srcBase) {
skvx::Vec<N, float> sum = 0.f;
for (int i = 0; i < fWindow; ++i) {
int s = (i + srcBase) % fWindow;
sum += fSrcBuffer[s] * fKernel[i];
}
return skvx::cast<uint8_t>(skvx::pin(sum * 255.f + 0.5f,
skvx::Vec<N, float>(0.f),
skvx::Vec<N, float>(255.f)));
};
while (n-- > 0) {
skvx::Vec<N, float> leadingEdge = srcPtr
? skvx::cast<float>(skvx::Vec<N, uint8_t>::Load(srcPtr)) * (1 / 255.0f)
: skvx::Vec<N, float>(0.f);
// Load the new leading edge into the circular buffer.
fSrcBuffer[(base + fWindow - 1) % fWindow] = leadingEdge;
// Perform the convolution and store the result.
if (dstPtr) {
convolve(base).store(dstPtr);
dstPtr += dstStride;
}
// Advance the source pointer (if it exists) and the circular buffer base.
if (srcPtr) {
srcPtr += srcStride;
}
base = (base + 1) % fWindow;
}
fSrcBufferBase = base;
}
const int fWindow;
float* fKernel;
skvx::Vec<N, float>* fSrcBuffer;
int fSrcBufferBase;
};
// Implement a scanline processor that uses a three-box filter to approximate a Gaussian blur.
// The ThreeBoxApproxPass is limit to processing sigmas < 135.
class ThreeBoxApproxPass final : public Pass {
public:
// NB 136 is the largest sigma that will not cause a buffer full of 255 mask values to overflow
// using the Gauss filter. It also limits the size of buffers used hold intermediate values.
// Explanation of maximums:
// sum0 = window * 255
// sum1 = window * sum0 -> window * window * 255
// sum2 = window * sum1 -> window * window * window * 255 -> window^3 * 255
//
// The value window^3 * 255 must fit in a uint32_t. So,
// window^3 < 2^32. window = 255.
//
// window = floor(sigma * 3 * sqrt(2 * kPi) / 4 + 0.5)
// For window <= 255, the largest value for sigma is 136.
static PassMaker* MakeMaker(float sigma, SkArenaAlloc* alloc) {
SkASSERT(0 <= sigma);
int window = SkBlurEngine::BoxBlurWindow(sigma);
if (255 <= window) {
return nullptr;
}
class Maker : public PassMaker {
public:
explicit Maker(int window, float sigma) : PassMaker{window, sigma} {}
Pass* makePass(void* buffer, SkArenaAlloc* alloc) const override {
return ThreeBoxApproxPass::Make(this->window(), buffer, alloc);
}
size_t bufferSizeBytes() const override {
int window = this->window();
size_t onePassSize = window - 1;
// If the window is odd, then there is an obvious middle element. For even sizes
// 2 passes are shifted, and the last pass has an extra element. Like this:
// S
// aaaAaa
// bbBbbb
// cccCccc
// D
size_t bufferCount = (window & 1) == 1 ? 3 * onePassSize : 3 * onePassSize + 1;
return bufferCount * sizeof(skvx::Vec<4, uint32_t>);
}
};
return alloc->make<Maker>(window, sigma);
}
static ThreeBoxApproxPass* Make(int window, void* buffers, SkArenaAlloc* alloc) {
// We don't need to store the trailing edge pixel in the buffer;
int passSize = window - 1;
skvx::Vec<4, uint32_t>* buffer0 = static_cast<skvx::Vec<4, uint32_t>*>(buffers);
skvx::Vec<4, uint32_t>* buffer1 = buffer0 + passSize;
skvx::Vec<4, uint32_t>* buffer2 = buffer1 + passSize;
// If the window is odd just one buffer is needed, but if it's even, then there is one
// more element on that pass.
skvx::Vec<4, uint32_t>* buffersEnd = buffer2 + ((window & 1) ? passSize : passSize + 1);
// Calculating the border is tricky. The border is the distance in pixels between the first
// dst pixel and the first src pixel (or the last src pixel and the last dst pixel).
// I will go through the odd case which is simpler, and then through the even case. Given a
// stack of filters seven wide for the odd case of three passes.
//
// S
// aaaAaaa
// bbbBbbb
// cccCccc
// D
//
// The furthest changed pixel is when the filters are in the following configuration.
//
// S
// aaaAaaa
// bbbBbbb
// cccCccc
// D
//
// The A pixel is calculated using the value S, the B uses A, and the C uses B, and
// finally D is C. So, with a window size of seven the border is nine. In the odd case, the
// border is 3*((window - 1)/2).
//
// For even cases the filter stack is more complicated. The spec specifies two passes
// of even filters and a final pass of odd filters. A stack for a width of six looks like
// this.
//
// S
// aaaAaa
// bbBbbb
// cccCccc
// D
//
// The furthest pixel looks like this.
//
// S
// aaaAaa
// bbBbbb
// cccCccc
// D
//
// For a window of six, the border value is eight. In the even case the border is 3 *
// (window/2) - 1.
int border = (window & 1) == 1 ? 3 * ((window - 1) / 2) : 3 * (window / 2) - 1;
// If the window is odd then the divisor is just window ^ 3 otherwise,
// it is window * window * (window + 1) = window ^ 3 + window ^ 2;
int window2 = window * window;
int window3 = window2 * window;
int divisor = (window & 1) == 1 ? window3 : window3 + window2;
return alloc->make<ThreeBoxApproxPass>(buffer0, buffer1, buffer2,
buffersEnd, border, divisor);
}
ThreeBoxApproxPass(skvx::Vec<4, uint32_t>* buffer0,
skvx::Vec<4, uint32_t>* buffer1,
skvx::Vec<4, uint32_t>* buffer2,
skvx::Vec<4, uint32_t>* buffersEnd,
int border,
int divisor)
: Pass{border}
, fBuffer0{buffer0}
, fBuffer1{buffer1}
, fBuffer2{buffer2}
, fBuffersEnd{buffersEnd}
, fDivider(divisor) {}
private:
void startBlur() override {
skvx::Vec<4, uint32_t> zero = {0u, 0u, 0u, 0u};
zero.store(fSum0);
zero.store(fSum1);
auto half = fDivider.half();
skvx::Vec<4, uint32_t>{half, half, half, half}.store(fSum2);
sk_bzero(fBuffer0, (fBuffersEnd - fBuffer0) * sizeof(skvx::Vec<4, uint32_t>));
fBuffer0Cursor = fBuffer0;
fBuffer1Cursor = fBuffer1;
fBuffer2Cursor = fBuffer2;
}
// GaussPass implements the common three pass box filter approximation of Gaussian blur,
// but combines all three passes into a single pass. This approach is facilitated by three
// circular buffers the width of the window which track values for trailing edges of each of
// the three passes. This allows the algorithm to use more precision in the calculation
// because the values are not rounded each pass. And this implementation also avoids a trap
// that's easy to fall into resulting in blending in too many zeroes near the edge.
//
// In general, a window sum has the form:
// sum_n+1 = sum_n + leading_edge - trailing_edge.
// If instead we do the subtraction at the end of the previous iteration, we can just
// calculate the sums instead of having to do the subtractions too.
//
// In previous iteration:
// sum_n+1 = sum_n - trailing_edge.
//
// In this iteration:
// sum_n+1 = sum_n + leading_edge.
//
// Now we can stack all three sums and do them at once. Sum0 gets its leading edge from the
// actual data. Sum1's leading edge is just Sum0, and Sum2's leading edge is Sum1. So, doing the
// three passes at the same time has the form:
//
// sum0_n+1 = sum0_n + leading edge
// sum1_n+1 = sum1_n + sum0_n+1
// sum2_n+1 = sum2_n + sum1_n+1
//
// sum2_n+1 / window^3 is the new value of the destination pixel.
//
// Reduce the sums by the trailing edges which were stored in the circular buffers for the
// next go around. This is the case for odd sized windows, even windows the the third
// circular buffer is one larger then the first two circular buffers.
//
// sum2_n+2 = sum2_n+1 - buffer2[i];
// buffer2[i] = sum1;
// sum1_n+2 = sum1_n+1 - buffer1[i];
// buffer1[i] = sum0;
// sum0_n+2 = sum0_n+1 - buffer0[i];
// buffer0[i] = leading edge
void blurSegment(
int n, const void* src, int srcStride, void* dst, int dstStride) override {
const uint32_t* src32 = reinterpret_cast<const uint32_t*>(src);
uint32_t* dst32 = reinterpret_cast<uint32_t*>(dst);
#if SK_CPU_LSX_LEVEL >= SK_CPU_LSX_LEVEL_LSX
skvx::Vec<4, uint32_t>* buffer0Cursor = fBuffer0Cursor;
skvx::Vec<4, uint32_t>* buffer1Cursor = fBuffer1Cursor;
skvx::Vec<4, uint32_t>* buffer2Cursor = fBuffer2Cursor;
v4u32 sum0 = __lsx_vld(fSum0, 0); // same as skvx::Vec<4, uint32_t>::Load(fSum0);
v4u32 sum1 = __lsx_vld(fSum1, 0);
v4u32 sum2 = __lsx_vld(fSum2, 0);
auto processValue = [&](v4u32& vLeadingEdge){
sum0 += vLeadingEdge;
sum1 += sum0;
sum2 += sum1;
v4u32 divisorFactor = __lsx_vreplgr2vr_w(fDivider.divisorFactor());
v4u32 blurred = __lsx_vmuh_w(divisorFactor, sum2);
v4u32 buffer2Value = __lsx_vld(buffer2Cursor, 0); //Not fBuffer0Cursor, out of bounds.
sum2 -= buffer2Value;
__lsx_vst(sum1, (void *)buffer2Cursor, 0);
buffer2Cursor = (buffer2Cursor + 1) < fBuffersEnd ? buffer2Cursor + 1 : fBuffer2;
v4u32 buffer1Value = __lsx_vld(buffer1Cursor, 0);
sum1 -= buffer1Value;
__lsx_vst(sum0, (void *)buffer1Cursor, 0);
buffer1Cursor = (buffer1Cursor + 1) < fBuffer2 ? buffer1Cursor + 1 : fBuffer1;
v4u32 buffer0Value = __lsx_vld(buffer0Cursor, 0);
sum0 -= buffer0Value;
__lsx_vst(vLeadingEdge, (void *)buffer0Cursor, 0);
buffer0Cursor = (buffer0Cursor + 1) < fBuffer1 ? buffer0Cursor + 1 : fBuffer0;
v16u8 shuf = {0x0,0x4,0x8,0xc,0x0};
v16u8 ret = __lsx_vshuf_b(blurred, blurred, shuf);
return ret;
};
v4u32 zero = __lsx_vldi(0x0);
if (!src32 && !dst32) {
while (n --> 0) {
(void)processValue(zero);
}
} else if (src32 && !dst32) {
while (n --> 0) {
v4u32 edge = __lsx_vinsgr2vr_w(zero, *src32, 0);
edge = __lsx_vilvl_b(zero, edge);
edge = __lsx_vilvl_h(zero, edge);
(void)processValue(edge);
src32 += srcStride;
}
} else if (!src32 && dst32) {
while (n --> 0) {
v4u32 ret = processValue(zero);
__lsx_vstelm_w(ret, dst32, 0, 0); // 3rd is offset, 4th is idx.
dst32 += dstStride;
}
} else if (src32 && dst32) {
while (n --> 0) {
v4u32 edge = __lsx_vinsgr2vr_w(zero, *src32, 0);
edge = __lsx_vilvl_b(zero, edge);
edge = __lsx_vilvl_h(zero, edge);
v4u32 ret = processValue(edge);
__lsx_vstelm_w(ret, dst32, 0, 0);
src32 += srcStride;
dst32 += dstStride;
}
}
// Store the state
fBuffer0Cursor = buffer0Cursor;
fBuffer1Cursor = buffer1Cursor;
fBuffer2Cursor = buffer2Cursor;
__lsx_vst(sum0, fSum0, 0);
__lsx_vst(sum1, fSum1, 0);
__lsx_vst(sum2, fSum2, 0);
#else
skvx::Vec<4, uint32_t>* buffer0Cursor = fBuffer0Cursor;
skvx::Vec<4, uint32_t>* buffer1Cursor = fBuffer1Cursor;
skvx::Vec<4, uint32_t>* buffer2Cursor = fBuffer2Cursor;
skvx::Vec<4, uint32_t> sum0 = skvx::Vec<4, uint32_t>::Load(fSum0);
skvx::Vec<4, uint32_t> sum1 = skvx::Vec<4, uint32_t>::Load(fSum1);
skvx::Vec<4, uint32_t> sum2 = skvx::Vec<4, uint32_t>::Load(fSum2);
// Given an expanded input pixel, move the window ahead using the leadingEdge value.
auto processValue = [&](const skvx::Vec<4, uint32_t>& leadingEdge) {
sum0 += leadingEdge;
sum1 += sum0;
sum2 += sum1;
skvx::Vec<4, uint32_t> blurred = fDivider.divide(sum2);
sum2 -= *buffer2Cursor;
*buffer2Cursor = sum1;
buffer2Cursor = (buffer2Cursor + 1) < fBuffersEnd ? buffer2Cursor + 1 : fBuffer2;
sum1 -= *buffer1Cursor;
*buffer1Cursor = sum0;
buffer1Cursor = (buffer1Cursor + 1) < fBuffer2 ? buffer1Cursor + 1 : fBuffer1;
sum0 -= *buffer0Cursor;
*buffer0Cursor = leadingEdge;
buffer0Cursor = (buffer0Cursor + 1) < fBuffer1 ? buffer0Cursor + 1 : fBuffer0;
return skvx::cast<uint8_t>(blurred);
};
auto loadEdge = [&](const uint32_t* srcCursor) {
return skvx::cast<uint32_t>(skvx::Vec<4, uint8_t>::Load(srcCursor));
};
if (!src32 && !dst32) {
while (n --> 0) {
(void)processValue(0);
}
} else if (src32 && !dst32) {
while (n --> 0) {
(void)processValue(loadEdge(src32));
src32 += srcStride;
}
} else if (!src32 && dst32) {
while (n --> 0) {
processValue(0u).store(dst32);
dst32 += dstStride;
}
} else if (src32 && dst32) {
while (n --> 0) {
processValue(loadEdge(src32)).store(dst32);
src32 += srcStride;
dst32 += dstStride;
}
}
// Store the state
fBuffer0Cursor = buffer0Cursor;
fBuffer1Cursor = buffer1Cursor;
fBuffer2Cursor = buffer2Cursor;
sum0.store(fSum0);
sum1.store(fSum1);
sum2.store(fSum2);
#endif
}
skvx::Vec<4, uint32_t>* const fBuffer0;
skvx::Vec<4, uint32_t>* const fBuffer1;
skvx::Vec<4, uint32_t>* const fBuffer2;
skvx::Vec<4, uint32_t>* const fBuffersEnd;
const skvx::ScaledDividerU32 fDivider;
// blur state
char fSum0[sizeof(skvx::Vec<4, uint32_t>)];
char fSum1[sizeof(skvx::Vec<4, uint32_t>)];
char fSum2[sizeof(skvx::Vec<4, uint32_t>)];
skvx::Vec<4, uint32_t>* fBuffer0Cursor;
skvx::Vec<4, uint32_t>* fBuffer1Cursor;
skvx::Vec<4, uint32_t>* fBuffer2Cursor;
};
// Implement a scanline processor that uses a two-box filter to approximate a Tent filter.
// The TentPass is limit to processing sigmas < 2183.
class TentPass final : public Pass {
public:
// NB 2183 is the largest sigma that will not cause a buffer full of 255 mask values to overflow
// using the Tent filter. It also limits the size of buffers used hold intermediate values.
// Explanation of maximums:
// sum0 = window * 255
// sum1 = window * sum0 -> window * window * 255
//
// The value window^2 * 255 must fit in a uint32_t. So,
// window^2 < 2^32. window = 4104.
//
// window = floor(sigma * 3 * sqrt(2 * kPi) / 4 + 0.5)
// For window <= 4104, the largest value for sigma is 2183.
static PassMaker* MakeMaker(float sigma, SkArenaAlloc* alloc) {
SkASSERT(0 <= sigma);
int gaussianWindow = SkBlurEngine::BoxBlurWindow(sigma);
// This is a naive method of using the window size for the Gaussian blur to calculate the
// window size for the Tent blur. This seems to work well in practice.
//
// We can use a single pixel to generate the effective blur area given a window size. For
// the Gaussian blur this is 3 * window size. For the Tent filter this is 2 * window size.
int tentWindow = 3 * gaussianWindow / 2;
if (tentWindow >= 4104) {
return nullptr;
}
class Maker : public PassMaker {
public:
explicit Maker(int window, float sigma) : PassMaker{window, sigma} {}
Pass* makePass(void* buffer, SkArenaAlloc* alloc) const override {
return TentPass::Make(this->window(), buffer, alloc);
}
size_t bufferSizeBytes() const override {
size_t onePassSize = this->window() - 1;
// If the window is odd, then there is an obvious middle element. For even sizes 2
// passes are shifted, and the last pass has an extra element. Like this:
// S
// aaaAaa
// bbBbbb
// D
size_t bufferCount = 2 * onePassSize;
return bufferCount * sizeof(skvx::Vec<4, uint32_t>);
}
};
return alloc->make<Maker>(tentWindow, sigma);
}
static TentPass* Make(int window, void* buffers, SkArenaAlloc* alloc) {
if (window > 4104) {
return nullptr;
}
// We don't need to store the trailing edge pixel in the buffer;
int passSize = window - 1;
skvx::Vec<4, uint32_t>* buffer0 = static_cast<skvx::Vec<4, uint32_t>*>(buffers);
skvx::Vec<4, uint32_t>* buffer1 = buffer0 + passSize;
skvx::Vec<4, uint32_t>* buffersEnd = buffer1 + passSize;
// Calculating the border is tricky. The border is the distance in pixels between the first
// dst pixel and the first src pixel (or the last src pixel and the last dst pixel).
// I will go through the odd case which is simpler, and then through the even case. Given a
// stack of filters seven wide for the odd case of three passes.
//
// S
// aaaAaaa
// bbbBbbb
// D
//
// The furthest changed pixel is when the filters are in the following configuration.
//
// S
// aaaAaaa
// bbbBbbb
// D
//
// The A pixel is calculated using the value S, the B uses A, and the D uses B.
// So, with a window size of seven the border is nine. In the odd case, the border is
// window - 1.
//
// For even cases the filter stack is more complicated. It uses two passes
// of even filters offset from each other. A stack for a width of six looks like
// this.
//
// S
// aaaAaa
// bbBbbb
// D
//
// The furthest pixel looks like this.
//
// S
// aaaAaa
// bbBbbb
// D
//
// For a window of six, the border value is 5. In the even case the border is
// window - 1.
int border = window - 1;
int divisor = window * window;
return alloc->make<TentPass>(buffer0, buffer1, buffersEnd, border, divisor);
}
TentPass(skvx::Vec<4, uint32_t>* buffer0,
skvx::Vec<4, uint32_t>* buffer1,
skvx::Vec<4, uint32_t>* buffersEnd,
int border,
int divisor)
: Pass{border}
, fBuffer0{buffer0}
, fBuffer1{buffer1}
, fBuffersEnd{buffersEnd}
, fDivider(divisor) {}
private:
void startBlur() override {
skvx::Vec<4, uint32_t>{0u, 0u, 0u, 0u}.store(fSum0);
auto half = fDivider.half();
skvx::Vec<4, uint32_t>{half, half, half, half}.store(fSum1);
sk_bzero(fBuffer0, (fBuffersEnd - fBuffer0) * sizeof(skvx::Vec<4, uint32_t>));
fBuffer0Cursor = fBuffer0;
fBuffer1Cursor = fBuffer1;
}
// TentPass implements the common two pass box filter approximation of Tent filter,
// but combines all both passes into a single pass. This approach is facilitated by two
// circular buffers the width of the window which track values for trailing edges of each of
// both passes. This allows the algorithm to use more precision in the calculation
// because the values are not rounded each pass. And this implementation also avoids a trap
// that's easy to fall into resulting in blending in too many zeroes near the edge.
//
// In general, a window sum has the form:
// sum_n+1 = sum_n + leading_edge - trailing_edge.
// If instead we do the subtraction at the end of the previous iteration, we can just
// calculate the sums instead of having to do the subtractions too.
//
// In previous iteration:
// sum_n+1 = sum_n - trailing_edge.
//
// In this iteration:
// sum_n+1 = sum_n + leading_edge.
//
// Now we can stack all three sums and do them at once. Sum0 gets its leading edge from the
// actual data. Sum1's leading edge is just Sum0, and Sum2's leading edge is Sum1. So, doing the
// three passes at the same time has the form:
//
// sum0_n+1 = sum0_n + leading edge
// sum1_n+1 = sum1_n + sum0_n+1
//
// sum1_n+1 / window^2 is the new value of the destination pixel.
//
// Reduce the sums by the trailing edges which were stored in the circular buffers for the
// next go around.
//
// sum1_n+2 = sum1_n+1 - buffer1[i];
// buffer1[i] = sum0;
// sum0_n+2 = sum0_n+1 - buffer0[i];
// buffer0[i] = leading edge
void blurSegment(
int n, const void* src, int srcStride, void* dst, int dstStride) override {
const uint32_t* src32 = reinterpret_cast<const uint32_t*>(src);
uint32_t* dst32 = reinterpret_cast<uint32_t*>(dst);
skvx::Vec<4, uint32_t>* buffer0Cursor = fBuffer0Cursor;
skvx::Vec<4, uint32_t>* buffer1Cursor = fBuffer1Cursor;
skvx::Vec<4, uint32_t> sum0 = skvx::Vec<4, uint32_t>::Load(fSum0);
skvx::Vec<4, uint32_t> sum1 = skvx::Vec<4, uint32_t>::Load(fSum1);
// Given an expanded input pixel, move the window ahead using the leadingEdge value.
auto processValue = [&](const skvx::Vec<4, uint32_t>& leadingEdge) {
sum0 += leadingEdge;
sum1 += sum0;
skvx::Vec<4, uint32_t> blurred = fDivider.divide(sum1);
sum1 -= *buffer1Cursor;
*buffer1Cursor = sum0;
buffer1Cursor = (buffer1Cursor + 1) < fBuffersEnd ? buffer1Cursor + 1 : fBuffer1;
sum0 -= *buffer0Cursor;
*buffer0Cursor = leadingEdge;
buffer0Cursor = (buffer0Cursor + 1) < fBuffer1 ? buffer0Cursor + 1 : fBuffer0;
return skvx::cast<uint8_t>(blurred);
};
auto loadEdge = [&](const uint32_t* srcCursor) {
return skvx::cast<uint32_t>(skvx::Vec<4, uint8_t>::Load(srcCursor));
};
if (!src32 && !dst32) {
while (n --> 0) {
(void)processValue(0);
}
} else if (src32 && !dst32) {
while (n --> 0) {
(void)processValue(loadEdge(src32));
src32 += srcStride;
}
} else if (!src32 && dst32) {
while (n --> 0) {
processValue(0u).store(dst32);
dst32 += dstStride;
}
} else if (src32 && dst32) {
while (n --> 0) {
processValue(loadEdge(src32)).store(dst32);
src32 += srcStride;
dst32 += dstStride;
}
}
// Store the state
fBuffer0Cursor = buffer0Cursor;
fBuffer1Cursor = buffer1Cursor;
sum0.store(fSum0);
sum1.store(fSum1);
}
skvx::Vec<4, uint32_t>* const fBuffer0;
skvx::Vec<4, uint32_t>* const fBuffer1;
skvx::Vec<4, uint32_t>* const fBuffersEnd;
const skvx::ScaledDividerU32 fDivider;
// blur state
char fSum0[sizeof(skvx::Vec<4, uint32_t>)];
char fSum1[sizeof(skvx::Vec<4, uint32_t>)];
skvx::Vec<4, uint32_t>* fBuffer0Cursor;
skvx::Vec<4, uint32_t>* fBuffer1Cursor;
};
class A8Pass final : public Pass {
public:
static PassMaker* MakeMaker(float sigma, SkArenaAlloc* alloc) {
SkASSERT(0 <= sigma);
int possibleWindow = static_cast<int>(floor(sigma * 3 * sqrt(2 * SK_DoublePI) / 4 + 0.5));
int window = std::max(1, possibleWindow);
class Maker : public PassMaker {
public:
explicit Maker(int window, float sigma) : PassMaker{window, sigma} {}
Pass* makePass(void* buffer, SkArenaAlloc* alloc) const override {
return A8Pass::Make(this->window(), buffer, alloc);
}
size_t bufferSizeBytes() const override {
int window = this->window();
size_t pass0Size = window - 1;
size_t pass1Size = window - 1;
size_t pass2Size = (window & 1) == 1 ? window - 1 : window;
return (pass0Size + pass1Size + pass2Size) * sizeof(uint32_t);
}
};
return alloc->make<Maker>(window, sigma);
}
static A8Pass* Make(int window, void* buffers, SkArenaAlloc* alloc) {
size_t pass0Size = window - 1;
size_t pass1Size = window - 1;
size_t pass2Size = (window & 1) == 1 ? window - 1 : window;
uint32_t* buffer0, *buffer0End, *buffer1, *buffer1End, *buffer2, *buffer2End;
buffer0 = static_cast<uint32_t*>(buffers);
buffer0End = buffer1 = buffer0 + pass0Size;
buffer1End = buffer2 = buffer1 + pass1Size;
buffer2End = buffer2 + pass2Size;
// Calculating the border is tricky. The border is the distance in pixels between the first
// dst pixel and the first src pixel (or the last src pixel and the last dst pixel).
// I will go through the odd case which is simpler, and then through the even case. Given a
// stack of filters seven wide for the odd case of three passes.
//
// S
// aaaAaaa
// bbbBbbb
// cccCccc
// D
//
// The furthest changed pixel is when the filters are in the following configuration.
//
// S
// aaaAaaa
// bbbBbbb
// cccCccc
// D
//
// The A pixel is calculated using the value S, the B uses A, and the C uses B, and
// finally D is C. So, with a window size of seven the border is nine. In the odd case, the
// border is 3*((window - 1)/2).
//
// For even cases the filter stack is more complicated. The spec specifies two passes
// of even filters and a final pass of odd filters. A stack for a width of six looks like
// this.
//
// S
// aaaAaa
// bbBbbb
// cccCccc
// D
//
// The furthest pixel looks like this.
//
// S
// aaaAaa
// bbBbbb
// cccCccc
// D
//
// For a window of six, the border value is eight. In the even case the border is 3 *
// (window/2) - 1.
int border = (window & 1) == 1 ? 3 * ((window - 1) / 2) : 3 * (window / 2) - 1;
// If the window is odd then the divisor is just window ^ 3 otherwise,
// it is window * window * (window + 1) = window ^ 2 + window ^ 3;
auto window2 = window * window;
auto window3 = window2 * window;
auto divisor = (window & 1) == 1 ? window3 : window3 + window2;
uint64_t weight = static_cast<uint64_t>(round(1.0 / divisor * (1ull << 32)));
return alloc->make<A8Pass>(weight, buffer0, buffer0End, buffer1, buffer1End,
buffer2, buffer2End, border);
}
A8Pass(uint64_t weight,
uint32_t* buffer0, uint32_t* buffer0End,
uint32_t* buffer1, uint32_t* buffer1End,
uint32_t* buffer2, uint32_t* buffer2End,
int border)
: Pass{border}
, fWeight(weight)
, fBuffer0{buffer0}
, fBuffer0End{buffer0End}
, fBuffer1{buffer1}
, fBuffer1End{buffer1End}
, fBuffer2{buffer2}
, fBuffer2End{buffer2End} {}
private:
void startBlur() override {
fSum0 = 0;
fSum1 = 0;
fSum2 = 0;
sk_bzero(fBuffer0, (fBuffer2End - fBuffer0) * sizeof(*fBuffer0));
fBuffer0Cursor = fBuffer0;
fBuffer1Cursor = fBuffer1;
fBuffer2Cursor = fBuffer2;
}
void blurSegment(
int n, const void* src, int srcStride, void* dst, int dstStride) override {
const uint8_t* src8 = reinterpret_cast<const uint8_t*>(src);
uint8_t* dst8 = reinterpret_cast<uint8_t*>(dst);
// If n is zero or negative, there's nothing to do.
if (n <= 0) {
return;
}
auto buffer0Cursor = fBuffer0Cursor;
auto buffer1Cursor = fBuffer1Cursor;
auto buffer2Cursor = fBuffer2Cursor;
uint32_t sum0 = fSum0;
uint32_t sum1 = fSum1;
uint32_t sum2 = fSum2;
auto processValue = [&](const uint32_t leadingEdge) {
sum0 += leadingEdge; sum1 += sum0; sum2 += sum1;
const uint8_t blurred = this->finalScale(sum2);
sum2 -= *buffer2Cursor; *buffer2Cursor = sum1;
buffer2Cursor = (buffer2Cursor + 1) < fBuffer2End ? buffer2Cursor + 1 : fBuffer2;
sum1 -= *buffer1Cursor; *buffer1Cursor = sum0;
buffer1Cursor = (buffer1Cursor + 1) < fBuffer1End ? buffer1Cursor + 1 : fBuffer1;
sum0 -= *buffer0Cursor; *buffer0Cursor = leadingEdge;
buffer0Cursor = (buffer0Cursor + 1) < fBuffer0End ? buffer0Cursor + 1 : fBuffer0;
return blurred;
};
if (!src8 && !dst8) {
while (n --> 0) {
(void)processValue(0);
}
} else if (src8 && !dst8) {
while (n --> 0) {
(void)processValue(*src8);
src8 += srcStride;
}
} else if (!src8 && dst8) {
while (n --> 0) {
*dst8 = processValue(0);
dst8 += dstStride;
}
} else if (src8 && dst8) {
while (n --> 0) {
*dst8 = processValue(*src8);
src8 += srcStride;
dst8 += dstStride;
}
}
// Store the updated state back into member variables for the next call.
fBuffer0Cursor = buffer0Cursor;
fBuffer1Cursor = buffer1Cursor;
fBuffer2Cursor = buffer2Cursor;
fSum0 = sum0;
fSum1 = sum1;
fSum2 = sum2;
}
inline static constexpr uint64_t kHalf = static_cast<uint64_t>(1) << 31;
uint8_t finalScale(uint32_t sum) const {
return SkTo<uint8_t>((fWeight * sum + kHalf) >> 32);
}
// While input data is only A8 (only needing uint8_t to store), we need to store
// single-channel 32-bit data for the accumulation calculations.
uint64_t fWeight;
uint32_t* fBuffer0;
uint32_t* fBuffer0End;
uint32_t* fBuffer1;
uint32_t* fBuffer1End;
uint32_t* fBuffer2;
uint32_t* fBuffer2End;
uint32_t* fBuffer0Cursor;
uint32_t* fBuffer1Cursor;
uint32_t* fBuffer2Cursor;
uint32_t fSum0;
uint32_t fSum1;
uint32_t fSum2;
};
class RasterA8BlurAlgorithm : public SkBlurEngine::Algorithm {
public:
// See analysis in description of GaussPass for the max supported sigma.
float maxSigma() const override {
static constexpr float kMaxSigma = 135.f;
SkASSERT(SkBlurEngine::BoxBlurWindow(kMaxSigma) <= 255);
return kMaxSigma;
}
// TODO: Implement CPU backend for different fTileMode. This is still worth doing inline with
// the blur; at the moment the tiling is applied via the CropImageFilter and carried as metadata
// on the FilterResult. This is forcefully applied in FilterResult::Builder::blur() when
// supportsOnlyDecalTiling() returns true.
bool supportsOnlyDecalTiling() const override { return true; }
sk_sp<SkSpecialImage> blur(SkSize sigma,
sk_sp<SkSpecialImage> input,
const SkIRect& originalSrcBounds,
SkTileMode tileMode,
const SkIRect& originalDstBounds) const override {
SkASSERT(tileMode == SkTileMode::kDecal);
SkASSERT(SkIRect::MakeSize(input->dimensions()).contains(originalSrcBounds));
SkBitmap src;
if (!SkSpecialImages::AsBitmap(input.get(), &src)) {
return nullptr; // Should only have been called by CPU-backed images
}
// The blur engine should not have picked this algorithm for a non-8-bit color type.
SkASSERT(src.colorType() == kAlpha_8_SkColorType);
// 1024 is a place holder guess until more analysis can be done.
SkSTArenaAlloc<1024> alloc;
auto makeMaker = [&](float sigma) -> PassMaker* {
SkASSERT(0 <= sigma && sigma <= 135); // should be guaranteed after map_sigma
if (PassMaker* maker = GaussianPass<uint8_t>::MakeMaker(sigma, &alloc)) {
return maker;
}
if (PassMaker* maker = A8Pass::MakeMaker(sigma, &alloc)) {
return maker;
}
SK_ABORT("Sigma is out of range.");
};
PassMaker* makerX = makeMaker(sigma.width());
PassMaker* makerY = makeMaker(sigma.height());
return eval_blur_passes<uint8_t>(makerX, makerY, src, originalSrcBounds,
originalDstBounds, &alloc);
}
};
class Raster8888BlurAlgorithm : public SkBlurEngine::Algorithm {
public:
// See analysis in description of TentPass for the max supported sigma.
float maxSigma() const override {
// TentPass supports a sigma up to 2183, and was added so that the CPU blur algorithm's
// blur radius was as large as that supported by the GPU. GaussPass only supports up to 136.
// However, there is a very apparent pop in blur weight when switching from successive box
// blurs to the tent filter. The TentPass is preserved for legacy blurs, which do not use
// FilterResult::rescale(). However, using kMaxSigma = 135 with the raster SkBlurEngine
// ensures that the non-legacy raster blurs will always use the GaussPass implementation.
// This is about 6-7x faster on large blurs to rescale a few times to a lower resolution
// than it is to evaluate the much larger original window.
static constexpr float kMaxSigma = 135.f;
SkASSERT(SkBlurEngine::BoxBlurWindow(kMaxSigma) <= 255); // see GaussPass::MakeMaker().
return kMaxSigma;
}
// TODO: Implement CPU backend for different fTileMode. This is still worth doing inline with
// the blur; at the moment the tiling is applied via the CropImageFilter and carried as metadata
// on the FilterResult. This is forcefully applied in FilterResult::Builder::blur() when
// supportsOnlyDecalTiling() returns true.
bool supportsOnlyDecalTiling() const override { return true; }
sk_sp<SkSpecialImage> blur(SkSize sigma,
sk_sp<SkSpecialImage> input,
const SkIRect& originalSrcBounds,
SkTileMode tileMode,
const SkIRect& originalDstBounds) const override {
// TODO: Enable this assert when the TentPass is no longer used for legacy blurs
// (which supports blur sigmas larger than what's reported in maxSigma()).
// SkASSERT(sigma.width() <= this->maxSigma() && sigma.height() <= this->maxSigma());
SkASSERT(tileMode == SkTileMode::kDecal);
SkASSERT(SkIRect::MakeSize(input->dimensions()).contains(originalSrcBounds));
SkBitmap src;
if (!SkSpecialImages::AsBitmap(input.get(), &src)) {
return nullptr; // Should only have been called by CPU-backed images
}
// The blur engine should not have picked this algorithm for a non-32-bit color type
SkASSERT(src.colorType() == kRGBA_8888_SkColorType ||
src.colorType() == kBGRA_8888_SkColorType);
SkSTArenaAlloc<1024> alloc;
auto makeMaker = [&](float sigma) -> PassMaker* {
SkASSERT(0 <= sigma && sigma <= 2183); // should be guaranteed after map_sigma
#ifndef SK_AVOID_SLOW_RASTER_PIPELINE_BLURS
if (PassMaker* maker = GaussianPass<uint32_t>::MakeMaker(sigma, &alloc)) {
return maker;
}
#endif //SK_AVOID_SLOW_RASTER_PIPELINE_BLURS
if (PassMaker* maker = ThreeBoxApproxPass::MakeMaker(sigma, &alloc)) {
return maker;
}
if (PassMaker* maker = TentPass::MakeMaker(sigma, &alloc)) {
return maker;
}
SK_ABORT("Sigma is out of range.");
};
PassMaker* makerX = makeMaker(sigma.width());
PassMaker* makerY = makeMaker(sigma.height());
return eval_blur_passes<uint32_t>(makerX, makerY, src, originalSrcBounds,
originalDstBounds, &alloc);
}
};
class RasterShaderBlurAlgorithm : public SkShaderBlurAlgorithm {
public:
sk_sp<SkDevice> makeDevice(const SkImageInfo& imageInfo) const override {
// This Device will only be used to draw blurs, so use default SkSurfaceProps. The pixel
// geometry and font configuration do not matter. This is not a GPU surface, so DMSAA and
// the kAlwaysDither surface property are also irrelevant.
return SkBitmapDevice::Create(imageInfo, SkSurfaceProps{});
}
};
class RasterBlurEngine : public SkBlurEngine {
public:
const Algorithm* findAlgorithm(SkSize sigma, SkColorType colorType) const override {
// The box blur doesn't actually care about channel order as long as it's 4 8-bit channels.
const bool rgba8Blur = colorType == kRGBA_8888_SkColorType ||
colorType == kBGRA_8888_SkColorType;
const bool a8Blur = colorType == kAlpha_8_SkColorType;
// For small sigmas, a8 and rgba blurs will use a gaussian blur, otherwise using
// box blur approximation.
if (a8Blur) {
return &fA8BlurAlgorithm;
} else if (rgba8Blur) {
return &fRGBA8BlurAlgorithm;
} else {
return &fShaderBlurAlgorithm;
}
}
private:
// For non-A8 or non-8888, use the shader algorithm
RasterShaderBlurAlgorithm fShaderBlurAlgorithm;
// For large blurs with RGBA8 or BGRA8, use consecutive box blurs,
// For small 8888 blurs, use gaussian blur
Raster8888BlurAlgorithm fRGBA8BlurAlgorithm;
// For any large blurs with A8, use consecutive box blurs,
// For small a8 blurs use gaussian blur
RasterA8BlurAlgorithm fA8BlurAlgorithm;
};
} // anonymous namespace
const SkBlurEngine* SkBlurEngine::GetRasterBlurEngine() {
static const RasterBlurEngine kInstance;
return &kInstance;
}
// SkShaderBlurAlgorithm
// ----------------------------------------------------------------------------
void SkShaderBlurAlgorithm::Compute2DBlurKernel(SkSize sigma,
SkISize radius,
SkSpan<float> kernel) {
// Callers likely had to calculate the radius prior to filling out the kernel value, which is
// why it's provided; but make sure it's consistent with expectations.
SkASSERT(SkBlurEngine::SigmaToRadius(sigma.width()) == radius.width() &&
SkBlurEngine::SigmaToRadius(sigma.height()) == radius.height());
// Callers are responsible for downscaling large sigmas to values that can be processed by the
// effects, so ensure the radius won't overflow 'kernel'
const int width = KernelWidth(radius.width());
const int height = KernelWidth(radius.height());
const size_t kernelSize = SkTo<size_t>(sk_64_mul(width, height));
SkASSERT(kernelSize <= kernel.size());
// And the definition of an identity blur should be sufficient that 2sigma^2 isn't near zero
// when there's a non-trivial radius.
const float twoSigmaSqrdX = 2.0f * sigma.width() * sigma.width();
const float twoSigmaSqrdY = 2.0f * sigma.height() * sigma.height();
SkASSERT((radius.width() == 0 || !SkScalarNearlyZero(twoSigmaSqrdX)) &&
(radius.height() == 0 || !SkScalarNearlyZero(twoSigmaSqrdY)));
// Setting the denominator to 1 when the radius is 0 automatically converts the remaining math
// to the 1D Gaussian distribution. When both radii are 0, it correctly computes a weight of 1.0
const float sigmaXDenom = radius.width() > 0 ? 1.0f / twoSigmaSqrdX : 1.f;
const float sigmaYDenom = radius.height() > 0 ? 1.0f / twoSigmaSqrdY : 1.f;
float sum = 0.0f;
for (int x = 0; x < width; x++) {
float xTerm = static_cast<float>(x - radius.width());
xTerm = xTerm * xTerm * sigmaXDenom;
for (int y = 0; y < height; y++) {
float yTerm = static_cast<float>(y - radius.height());
float xyTerm = std::exp(-(xTerm + yTerm * yTerm * sigmaYDenom));
// Note that the constant term (1/(sqrt(2*pi*sigma^2)) of the Gaussian
// is dropped here, since we renormalize the kernel below.
kernel[y * width + x] = xyTerm;
sum += xyTerm;
}
}
// Normalize the kernel
float scale = 1.0f / sum;
for (size_t i = 0; i < kernelSize; ++i) {
kernel[i] *= scale;
}
// Zero remainder of the array
memset(kernel.data() + kernelSize, 0, sizeof(float)*(kernel.size() - kernelSize));
}
void SkShaderBlurAlgorithm::Compute2DBlurKernel(SkSize sigma,
SkISize radii,
std::array<SkV4, kMaxSamples/4>& kernel) {
static_assert(sizeof(kernel) == sizeof(std::array<float, kMaxSamples>));
static_assert(alignof(float) == alignof(SkV4));
float* data = kernel[0].ptr();
Compute2DBlurKernel(sigma, radii, SkSpan<float>(data, kMaxSamples));
}
void SkShaderBlurAlgorithm::Compute2DBlurOffsets(SkISize radius,
std::array<SkV4, kMaxSamples/2>& offsets) {
const int kernelArea = KernelWidth(radius.width()) * KernelWidth(radius.height());
SkASSERT(kernelArea <= kMaxSamples);
SkSpan<float> offsetView{offsets[0].ptr(), kMaxSamples*2};
int i = 0;
for (int y = -radius.height(); y <= radius.height(); ++y) {
for (int x = -radius.width(); x <= radius.width(); ++x) {
offsetView[2*i] = x;
offsetView[2*i+1] = y;
++i;
}
}
SkASSERT(i == kernelArea);
const int lastValidOffset = 2*(kernelArea - 1);
for (; i < kMaxSamples; ++i) {
offsetView[2*i] = offsetView[lastValidOffset];
offsetView[2*i+1] = offsetView[lastValidOffset+1];
}
}
void SkShaderBlurAlgorithm::Compute1DBlurLinearKernel(
float sigma,
int radius,
std::array<SkV4, kMaxSamples/2>& offsetsAndKernel) {
SkASSERT(sigma <= kMaxLinearSigma);
SkASSERT(radius == SkBlurEngine::SigmaToRadius(sigma));
SkASSERT(LinearKernelWidth(radius) <= kMaxSamples);
// Given 2 adjacent gaussian points, they are blended as: Wi * Ci + Wj * Cj.
// The GPU will mix Ci and Cj as Ci * (1 - x) + Cj * x during sampling.
// Compute W', x such that W' * (Ci * (1 - x) + Cj * x) = Wi * Ci + Wj * Cj.
// Solving W' * x = Wj, W' * (1 - x) = Wi:
// W' = Wi + Wj
// x = Wj / (Wi + Wj)
auto get_new_weight = [](float* new_w, float* offset, float wi, float wj) {
*new_w = wi + wj;
*offset = wj / (wi + wj);
};
// Create a temporary standard kernel. The maximum blur radius that can be passed to this
// function is (kMaxBlurSamples-1), so make an array large enough to hold the full kernel width.
static constexpr int kMaxKernelWidth = KernelWidth(kMaxSamples - 1);
SkASSERT(KernelWidth(radius) <= kMaxKernelWidth);
std::array<float, kMaxKernelWidth> fullKernel;
Compute1DBlurKernel(sigma, radius, SkSpan<float>{fullKernel.data(), KernelWidth(radius)});
std::array<float, kMaxSamples> kernel;
std::array<float, kMaxSamples> offsets;
// Note that halfsize isn't just size / 2, but radius + 1. This is the size of the output array.
int halfSize = LinearKernelWidth(radius);
int halfRadius = halfSize / 2;
int lowIndex = halfRadius - 1;
// Compute1DGaussianKernel produces a full 2N + 1 kernel. Since the kernel can be mirrored,
// compute only the upper half and mirror to the lower half.
int index = radius;
if (radius & 1) {
// If N is odd, then use two samples.
// The centre texel gets sampled twice, so halve its influence for each sample.
// We essentially sample like this:
// Texel edges
// v v v v
// | | | |
// \-----^---/ Lower sample
// \---^-----/ Upper sample
get_new_weight(&kernel[halfRadius],
&offsets[halfRadius],
fullKernel[index] * 0.5f,
fullKernel[index + 1]);
kernel[lowIndex] = kernel[halfRadius];
offsets[lowIndex] = -offsets[halfRadius];
index++;
lowIndex--;
} else {
// If N is even, then there are an even number of texels on either side of the centre texel.
// Sample the centre texel directly.
kernel[halfRadius] = fullKernel[index];
offsets[halfRadius] = 0.0f;
}
index++;
// Every other pair gets one sample.
for (int i = halfRadius + 1; i < halfSize; index += 2, i++, lowIndex--) {
get_new_weight(&kernel[i], &offsets[i], fullKernel[index], fullKernel[index + 1]);
offsets[i] += static_cast<float>(index - radius);
// Mirror to lower half.
kernel[lowIndex] = kernel[i];
offsets[lowIndex] = -offsets[i];
}
// Zero out remaining values in the kernel
memset(kernel.data() + halfSize, 0, sizeof(float)*(kMaxSamples - halfSize));
// But copy the last valid offset into the remaining offsets, to increase the chance that
// over-iteration in a fragment shader will have a cache hit.
for (int i = halfSize; i < kMaxSamples; ++i) {
offsets[i] = offsets[halfSize - 1];
}
// Interleave into the output array to match the 1D SkSL effect
for (int i = 0; i < kMaxSamples / 2; ++i) {
offsetsAndKernel[i] = SkV4{offsets[2*i], kernel[2*i], offsets[2*i+1], kernel[2*i+1]};
}
}
static SkKnownRuntimeEffects::StableKey to_stablekey(int kernelWidth, uint32_t baseKey) {
SkASSERT(kernelWidth >= 2 && kernelWidth <= SkShaderBlurAlgorithm::kMaxSamples);
switch(kernelWidth) {
// Batch on multiples of 4 (skipping width=1, since that can't happen)
case 2: [[fallthrough]];
case 3: [[fallthrough]];
case 4: return static_cast<SkKnownRuntimeEffects::StableKey>(baseKey);
case 5: [[fallthrough]];
case 6: [[fallthrough]];
case 7: [[fallthrough]];
case 8: return static_cast<SkKnownRuntimeEffects::StableKey>(baseKey+1);
case 9: [[fallthrough]];
case 10: [[fallthrough]];
case 11: [[fallthrough]];
case 12: return static_cast<SkKnownRuntimeEffects::StableKey>(baseKey+2);
case 13: [[fallthrough]];
case 14: [[fallthrough]];
case 15: [[fallthrough]];
case 16: return static_cast<SkKnownRuntimeEffects::StableKey>(baseKey+3);
case 17: [[fallthrough]];
case 18: [[fallthrough]];
case 19: [[fallthrough]];
// With larger kernels, batch on multiples of eight so up to 7 wasted samples.
case 20: return static_cast<SkKnownRuntimeEffects::StableKey>(baseKey+4);
case 21: [[fallthrough]];
case 22: [[fallthrough]];
case 23: [[fallthrough]];
case 24: [[fallthrough]];
case 25: [[fallthrough]];
case 26: [[fallthrough]];
case 27: [[fallthrough]];
case 28: return static_cast<SkKnownRuntimeEffects::StableKey>(baseKey+5);
default:
SkUNREACHABLE;
}
}
const SkRuntimeEffect* SkShaderBlurAlgorithm::GetLinearBlur1DEffect(int radius) {
return GetKnownRuntimeEffect(
to_stablekey(LinearKernelWidth(radius),
static_cast<uint32_t>(SkKnownRuntimeEffects::StableKey::k1DBlurBase)));
}
const SkRuntimeEffect* SkShaderBlurAlgorithm::GetBlur2DEffect(const SkISize& radii) {
int kernelArea = KernelWidth(radii.width()) * KernelWidth(radii.height());
return GetKnownRuntimeEffect(
to_stablekey(kernelArea,
static_cast<uint32_t>(SkKnownRuntimeEffects::StableKey::k2DBlurBase)));
}
sk_sp<SkSpecialImage> SkShaderBlurAlgorithm::renderBlur(SkRuntimeShaderBuilder* blurEffectBuilder,
SkFilterMode filter,
SkISize radii,
sk_sp<SkSpecialImage> input,
const SkIRect& srcRect,
SkTileMode tileMode,
const SkIRect& dstRect) const {
SkImageInfo outII = SkImageInfo::Make({dstRect.width(), dstRect.height()},
input->colorType(),
kPremul_SkAlphaType,
input->colorInfo().refColorSpace());
sk_sp<SkDevice> device = this->makeDevice(outII);
if (!device) {
return nullptr;
}
SkIRect subset = SkIRect::MakeSize(dstRect.size());
device->clipRect(SkRect::Make(subset), SkClipOp::kIntersect, /*aa=*/false);
device->setLocalToDevice(SkM44::Translate(-dstRect.left(), -dstRect.top()));
// renderBlur() will either mix multiple fast and strict draws to cover dstRect, or will issue
// a single strict draw. While the SkShader object changes (really just strict mode), the rest
// of the SkPaint remains the same.
SkPaint paint;
paint.setBlendMode(SkBlendMode::kSrc);
SkIRect safeSrcRect = srcRect.makeInset(radii.width(), radii.height());
SkIRect fastDstRect = dstRect;
// Only consider the safeSrcRect for shader-based tiling if the original srcRect is different
// from the backing store dimensions; when they match the full image we can use HW tiling.
if (srcRect != SkIRect::MakeSize(input->backingStoreDimensions())) {
if (fastDstRect.intersect(safeSrcRect)) {
// If the area of the non-clamping shader is small, it's better to just issue a single
// draw that performs shader tiling over the whole dst.
if (fastDstRect != dstRect && fastDstRect.width() * fastDstRect.height() < 128 * 128) {
fastDstRect.setEmpty();
}
} else {
fastDstRect.setEmpty();
}
}
if (!fastDstRect.isEmpty()) {
// Fill as much as possible without adding shader tiling logic to each blur sample,
// switching to clamp tiling if we aren't in this block due to HW tiling.
SkIRect untiledSrcRect = srcRect.makeInset(1, 1);
SkTileMode fastTileMode = untiledSrcRect.contains(fastDstRect) ? SkTileMode::kClamp
: tileMode;
blurEffectBuilder->child("child") = input->asShader(
fastTileMode, filter, SkMatrix::I(), /*strict=*/false);
paint.setShader(blurEffectBuilder->makeShader());
device->drawRect(SkRect::Make(fastDstRect), paint);
}
// Switch to a strict shader if there are remaining pixels to fill
if (fastDstRect != dstRect) {
blurEffectBuilder->child("child") = input->makeSubset(srcRect)->asShader(
tileMode, filter, SkMatrix::Translate(srcRect.left(), srcRect.top()));
paint.setShader(blurEffectBuilder->makeShader());
}
if (fastDstRect.isEmpty()) {
// Fill the entire dst with the strict shader
device->drawRect(SkRect::Make(dstRect), paint);
} else if (fastDstRect != dstRect) {
// There will be up to four additional strict draws to fill in the border. The left and
// right sides will span the full height of the dst rect. The top and bottom will span
// the just the width of the fast interior. Strict border draws with zero width/height
// are skipped.
auto drawBorder = [&](const SkIRect& r) {
if (!r.isEmpty()) {
device->drawRect(SkRect::Make(r), paint);
}
};
drawBorder({dstRect.left(), dstRect.top(),
fastDstRect.left(), dstRect.bottom()}); // Left, spanning full height
drawBorder({fastDstRect.right(), dstRect.top(),
dstRect.right(), dstRect.bottom()}); // Right, spanning full height
drawBorder({fastDstRect.left(), dstRect.top(),
fastDstRect.right(), fastDstRect.top()}); // Top, spanning inner width
drawBorder({fastDstRect.left(), fastDstRect.bottom(),
fastDstRect.right(), dstRect.bottom()}); // Bottom, spanning inner width
}
return device->snapSpecial(subset);
}
sk_sp<SkSpecialImage> SkShaderBlurAlgorithm::evalBlur2D(SkSize sigma,
SkISize radii,
sk_sp<SkSpecialImage> input,
const SkIRect& srcRect,
SkTileMode tileMode,
const SkIRect& dstRect) const {
std::array<SkV4, kMaxSamples/4> kernel;
std::array<SkV4, kMaxSamples/2> offsets;
Compute2DBlurKernel(sigma, radii, kernel);
Compute2DBlurOffsets(radii, offsets);
SkRuntimeShaderBuilder builder{sk_ref_sp(GetBlur2DEffect(radii))};
builder.uniform("kernel") = kernel;
builder.uniform("offsets") = offsets;
// NOTE: renderBlur() will configure the "child" shader as needed. The 2D blur effect only
// requires nearest-neighbor filtering.
return this->renderBlur(&builder, SkFilterMode::kNearest, radii,
std::move(input), srcRect, tileMode, dstRect);
}
sk_sp<SkSpecialImage> SkShaderBlurAlgorithm::evalBlur1D(float sigma,
int radius,
SkV2 dir,
sk_sp<SkSpecialImage> input,
SkIRect srcRect,
SkTileMode tileMode,
SkIRect dstRect) const {
std::array<SkV4, kMaxSamples/2> offsetsAndKernel;
Compute1DBlurLinearKernel(sigma, radius, offsetsAndKernel);
SkRuntimeShaderBuilder builder{sk_ref_sp(GetLinearBlur1DEffect(radius))};
builder.uniform("offsetsAndKernel") = offsetsAndKernel;
builder.uniform("dir") = dir;
// NOTE: renderBlur() will configure the "child" shader as needed. The 1D blur effect requires
// linear filtering. Reconstruct the appropriate "2D" radii inset value from 'dir'.
SkISize radii{dir.x ? radius : 0, dir.y ? radius : 0};
return this->renderBlur(&builder, SkFilterMode::kLinear, radii,
std::move(input), srcRect, tileMode, dstRect);
}
sk_sp<SkSpecialImage> SkShaderBlurAlgorithm::blur(SkSize sigma,
sk_sp<SkSpecialImage> src,
const SkIRect& srcRect,
SkTileMode tileMode,
const SkIRect& dstRect) const {
SkASSERT(sigma.width() <= kMaxLinearSigma && sigma.height() <= kMaxLinearSigma);
int radiusX = SkBlurEngine::SigmaToRadius(sigma.width());
int radiusY = SkBlurEngine::SigmaToRadius(sigma.height());
const int kernelArea = KernelWidth(radiusX) * KernelWidth(radiusY);
if (kernelArea <= kMaxSamples && radiusX > 0 && radiusY > 0) {
// Use a single-pass 2D kernel if it fits and isn't just 1D already
return this->evalBlur2D(sigma,
{radiusX, radiusY},
std::move(src),
srcRect,
tileMode,
dstRect);
} else {
// Use two passes of a 1D kernel (one per axis).
SkIRect intermediateSrcRect = srcRect;
SkIRect intermediateDstRect = dstRect;
if (radiusX > 0) {
if (radiusY > 0) {
// May need to maintain extra rows above and below 'dstRect' for the follow-up pass.
if (tileMode == SkTileMode::kRepeat || tileMode == SkTileMode::kMirror) {
// If the srcRect and dstRect are aligned, then we don't need extra rows since
// the periodic tiling on srcRect is the same for the intermediate. If they
// are not aligned, then outset by the Y radius.
const int period = srcRect.height() * (tileMode == SkTileMode::kMirror ? 2 : 1);
if (std::abs(dstRect.fTop - srcRect.fTop) % period != 0 ||
dstRect.height() != srcRect.height()) {
intermediateDstRect.outset(0, radiusY);
}
} else {
// For clamp and decal tiling, we outset by the Y radius up to what's available
// from the srcRect. Anything beyond that is identical to tiling the
// intermediate dst image directly.
intermediateDstRect.outset(0, radiusY);
intermediateDstRect.fTop = std::max(intermediateDstRect.fTop, srcRect.fTop);
intermediateDstRect.fBottom =
std::min(intermediateDstRect.fBottom, srcRect.fBottom);
if (intermediateDstRect.fTop >= intermediateDstRect.fBottom) {
return nullptr;
}
}
}
src = this->evalBlur1D(sigma.width(),
radiusX,
/*dir=*/{1.f, 0.f},
std::move(src),
srcRect,
tileMode,
intermediateDstRect);
if (!src) {
return nullptr;
}
intermediateSrcRect = SkIRect::MakeWH(src->width(), src->height());
intermediateDstRect = dstRect.makeOffset(-intermediateDstRect.left(),
-intermediateDstRect.top());
}
if (radiusY > 0) {
src = this->evalBlur1D(sigma.height(),
radiusY,
/*dir=*/{0.f, 1.f},
std::move(src),
intermediateSrcRect,
tileMode,
intermediateDstRect);
}
return src;
}
}