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/*
* Copyright 2018 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
in half4 circleRect;
in half textureRadius;
in half solidRadius;
in uniform sampler2D blurProfileSampler;
// The data is formatted as:
// x, y - the center of the circle
// z - inner radius that should map to 0th entry in the texture.
// w - the inverse of the distance over which the texture is stretched.
uniform half4 circleData;
@optimizationFlags {
kCompatibleWithCoverageAsAlpha_OptimizationFlag
}
@make {
static std::unique_ptr<GrFragmentProcessor> Make(GrProxyProvider*,
const SkRect& circle, float sigma);
}
@setData(data) {
data.set4f(circleData, circleRect.centerX(), circleRect.centerY(), solidRadius,
1.f / textureRadius);
}
@cpp {
#include "src/gpu/GrProxyProvider.h"
// Computes an unnormalized half kernel (right side). Returns the summation of all the half
// kernel values.
static float make_unnormalized_half_kernel(float* halfKernel, int halfKernelSize, float sigma) {
const float invSigma = 1.f / sigma;
const float b = -0.5f * invSigma * invSigma;
float tot = 0.0f;
// Compute half kernel values at half pixel steps out from the center.
float t = 0.5f;
for (int i = 0; i < halfKernelSize; ++i) {
float value = expf(t * t * b);
tot += value;
halfKernel[i] = value;
t += 1.f;
}
return tot;
}
// Create a Gaussian half-kernel (right side) and a summed area table given a sigma and number
// of discrete steps. The half kernel is normalized to sum to 0.5.
static void make_half_kernel_and_summed_table(float* halfKernel, float* summedHalfKernel,
int halfKernelSize, float sigma) {
// The half kernel should sum to 0.5 not 1.0.
const float tot = 2.f * make_unnormalized_half_kernel(halfKernel, halfKernelSize, sigma);
float sum = 0.f;
for (int i = 0; i < halfKernelSize; ++i) {
halfKernel[i] /= tot;
sum += halfKernel[i];
summedHalfKernel[i] = sum;
}
}
// Applies the 1D half kernel vertically at points along the x axis to a circle centered at the
// origin with radius circleR.
void apply_kernel_in_y(float* results, int numSteps, float firstX, float circleR,
int halfKernelSize, const float* summedHalfKernelTable) {
float x = firstX;
for (int i = 0; i < numSteps; ++i, x += 1.f) {
if (x < -circleR || x > circleR) {
results[i] = 0;
continue;
}
float y = sqrtf(circleR * circleR - x * x);
// In the column at x we exit the circle at +y and -y
// The summed table entry j is actually reflects an offset of j + 0.5.
y -= 0.5f;
int yInt = SkScalarFloorToInt(y);
SkASSERT(yInt >= -1);
if (y < 0) {
results[i] = (y + 0.5f) * summedHalfKernelTable[0];
} else if (yInt >= halfKernelSize - 1) {
results[i] = 0.5f;
} else {
float yFrac = y - yInt;
results[i] = (1.f - yFrac) * summedHalfKernelTable[yInt] +
yFrac * summedHalfKernelTable[yInt + 1];
}
}
}
// Apply a Gaussian at point (evalX, 0) to a circle centered at the origin with radius circleR.
// This relies on having a half kernel computed for the Gaussian and a table of applications of
// the half kernel in y to columns at (evalX - halfKernel, evalX - halfKernel + 1, ..., evalX +
// halfKernel) passed in as yKernelEvaluations.
static uint8_t eval_at(float evalX, float circleR, const float* halfKernel, int halfKernelSize,
const float* yKernelEvaluations) {
float acc = 0;
float x = evalX - halfKernelSize;
for (int i = 0; i < halfKernelSize; ++i, x += 1.f) {
if (x < -circleR || x > circleR) {
continue;
}
float verticalEval = yKernelEvaluations[i];
acc += verticalEval * halfKernel[halfKernelSize - i - 1];
}
for (int i = 0; i < halfKernelSize; ++i, x += 1.f) {
if (x < -circleR || x > circleR) {
continue;
}
float verticalEval = yKernelEvaluations[i + halfKernelSize];
acc += verticalEval * halfKernel[i];
}
// Since we applied a half kernel in y we multiply acc by 2 (the circle is symmetric about
// the x axis).
return SkUnitScalarClampToByte(2.f * acc);
}
// This function creates a profile of a blurred circle. It does this by computing a kernel for
// half the Gaussian and a matching summed area table. The summed area table is used to compute
// an array of vertical applications of the half kernel to the circle along the x axis. The
// table of y evaluations has 2 * k + n entries where k is the size of the half kernel and n is
// the size of the profile being computed. Then for each of the n profile entries we walk out k
// steps in each horizontal direction multiplying the corresponding y evaluation by the half
// kernel entry and sum these values to compute the profile entry.
static void create_circle_profile(uint8_t* weights, float sigma, float circleR,
int profileTextureWidth) {
const int numSteps = profileTextureWidth;
// The full kernel is 6 sigmas wide.
int halfKernelSize = SkScalarCeilToInt(6.0f * sigma);
// round up to next multiple of 2 and then divide by 2
halfKernelSize = ((halfKernelSize + 1) & ~1) >> 1;
// Number of x steps at which to apply kernel in y to cover all the profile samples in x.
int numYSteps = numSteps + 2 * halfKernelSize;
SkAutoTArray<float> bulkAlloc(halfKernelSize + halfKernelSize + numYSteps);
float* halfKernel = bulkAlloc.get();
float* summedKernel = bulkAlloc.get() + halfKernelSize;
float* yEvals = bulkAlloc.get() + 2 * halfKernelSize;
make_half_kernel_and_summed_table(halfKernel, summedKernel, halfKernelSize, sigma);
float firstX = -halfKernelSize + 0.5f;
apply_kernel_in_y(yEvals, numYSteps, firstX, circleR, halfKernelSize, summedKernel);
for (int i = 0; i < numSteps - 1; ++i) {
float evalX = i + 0.5f;
weights[i] = eval_at(evalX, circleR, halfKernel, halfKernelSize, yEvals + i);
}
// Ensure the tail of the Gaussian goes to zero.
weights[numSteps - 1] = 0;
}
static void create_half_plane_profile(uint8_t* profile, int profileWidth) {
SkASSERT(!(profileWidth & 0x1));
// The full kernel is 6 sigmas wide.
float sigma = profileWidth / 6.f;
int halfKernelSize = profileWidth / 2;
SkAutoTArray<float> halfKernel(halfKernelSize);
// The half kernel should sum to 0.5.
const float tot = 2.f * make_unnormalized_half_kernel(halfKernel.get(), halfKernelSize,
sigma);
float sum = 0.f;
// Populate the profile from the right edge to the middle.
for (int i = 0; i < halfKernelSize; ++i) {
halfKernel[halfKernelSize - i - 1] /= tot;
sum += halfKernel[halfKernelSize - i - 1];
profile[profileWidth - i - 1] = SkUnitScalarClampToByte(sum);
}
// Populate the profile from the middle to the left edge (by flipping the half kernel and
// continuing the summation).
for (int i = 0; i < halfKernelSize; ++i) {
sum += halfKernel[i];
profile[halfKernelSize - i - 1] = SkUnitScalarClampToByte(sum);
}
// Ensure tail goes to 0.
profile[profileWidth - 1] = 0;
}
static sk_sp<GrTextureProxy> create_profile_texture(GrProxyProvider* proxyProvider,
const SkRect& circle,
float sigma,
float* solidRadius, float* textureRadius) {
float circleR = circle.width() / 2.0f;
if (circleR < SK_ScalarNearlyZero) {
return nullptr;
}
// Profile textures are cached by the ratio of sigma to circle radius and by the size of the
// profile texture (binned by powers of 2).
SkScalar sigmaToCircleRRatio = sigma / circleR;
// When sigma is really small this becomes a equivalent to convolving a Gaussian with a
// half-plane. Similarly, in the extreme high ratio cases circle becomes a point WRT to the
// Guassian and the profile texture is a just a Gaussian evaluation. However, we haven't yet
// implemented this latter optimization.
sigmaToCircleRRatio = SkTMin(sigmaToCircleRRatio, 8.f);
SkFixed sigmaToCircleRRatioFixed;
static const SkScalar kHalfPlaneThreshold = 0.1f;
bool useHalfPlaneApprox = false;
if (sigmaToCircleRRatio <= kHalfPlaneThreshold) {
useHalfPlaneApprox = true;
sigmaToCircleRRatioFixed = 0;
*solidRadius = circleR - 3 * sigma;
*textureRadius = 6 * sigma;
} else {
// Convert to fixed point for the key.
sigmaToCircleRRatioFixed = SkScalarToFixed(sigmaToCircleRRatio);
// We shave off some bits to reduce the number of unique entries. We could probably
// shave off more than we do.
sigmaToCircleRRatioFixed &= ~0xff;
sigmaToCircleRRatio = SkFixedToScalar(sigmaToCircleRRatioFixed);
sigma = circleR * sigmaToCircleRRatio;
*solidRadius = 0;
*textureRadius = circleR + 3 * sigma;
}
static const GrUniqueKey::Domain kDomain = GrUniqueKey::GenerateDomain();
GrUniqueKey key;
GrUniqueKey::Builder builder(&key, kDomain, 1, "1-D Circular Blur");
builder[0] = sigmaToCircleRRatioFixed;
builder.finish();
sk_sp<GrTextureProxy> blurProfile = proxyProvider->findOrCreateProxyByUniqueKey(
key, GrColorType::kAlpha_8, kTopLeft_GrSurfaceOrigin);
if (!blurProfile) {
static constexpr int kProfileTextureWidth = 512;
SkBitmap bm;
if (!bm.tryAllocPixels(SkImageInfo::MakeA8(kProfileTextureWidth, 1))) {
return nullptr;
}
if (useHalfPlaneApprox) {
create_half_plane_profile(bm.getAddr8(0, 0), kProfileTextureWidth);
} else {
// Rescale params to the size of the texture we're creating.
SkScalar scale = kProfileTextureWidth / *textureRadius;
create_circle_profile(bm.getAddr8(0, 0), sigma * scale, circleR * scale,
kProfileTextureWidth);
}
bm.setImmutable();
sk_sp<SkImage> image = SkImage::MakeFromBitmap(bm);
blurProfile = proxyProvider->createTextureProxy(std::move(image), 1,
SkBudgeted::kYes, SkBackingFit::kExact);
if (!blurProfile) {
return nullptr;
}
SkASSERT(blurProfile->origin() == kTopLeft_GrSurfaceOrigin);
proxyProvider->assignUniqueKeyToProxy(key, blurProfile.get());
}
return blurProfile;
}
std::unique_ptr<GrFragmentProcessor> GrCircleBlurFragmentProcessor::Make(
GrProxyProvider* proxyProvider, const SkRect& circle, float sigma) {
float solidRadius;
float textureRadius;
sk_sp<GrTextureProxy> profile(create_profile_texture(proxyProvider, circle, sigma,
&solidRadius, &textureRadius));
if (!profile) {
return nullptr;
}
return std::unique_ptr<GrFragmentProcessor>(new GrCircleBlurFragmentProcessor(
circle, textureRadius, solidRadius, std::move(profile)));
}
}
void main() {
// We just want to compute "(length(vec) - circleData.z + 0.5) * circleData.w" but need to
// rearrange for precision.
half2 vec = half2(half((sk_FragCoord.x - circleData.x) * circleData.w),
half((sk_FragCoord.y - circleData.y) * circleData.w));
half dist = length(vec) + (0.5 - circleData.z) * circleData.w;
sk_OutColor = sk_InColor * sample(blurProfileSampler, half2(dist, 0.5)).a;
}
@test(testData) {
SkScalar wh = testData->fRandom->nextRangeScalar(100.f, 1000.f);
SkScalar sigma = testData->fRandom->nextRangeF(1.f,10.f);
SkRect circle = SkRect::MakeWH(wh, wh);
return GrCircleBlurFragmentProcessor::Make(testData->proxyProvider(), circle, sigma);
}