chromium/third_party/skia/src/gpu/BlurUtils.cpp

/*
 * Copyright 2023 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#include "src/gpu/BlurUtils.h"

#include "include/core/SkBitmap.h"
#include "include/core/SkColorPriv.h"
#include "include/core/SkImageInfo.h"
#include "include/core/SkRRect.h"
#include "include/core/SkRect.h"
#include "include/core/SkScalar.h"
#include "include/core/SkSize.h"
#include "include/private/base/SkAssert.h"
#include "include/private/base/SkFloatingPoint.h"
#include "include/private/base/SkMath.h"
#include "include/private/base/SkPoint_impl.h"
#include "include/private/base/SkTemplates.h"
#include "include/private/base/SkTo.h"
#include "src/base/SkMathPriv.h"

#include <algorithm>
#include <cmath>
#include <cstdint>
#include <cstring>
#include <memory>
#include <vector>

namespace skgpu {

///////////////////////////////////////////////////////////////////////////////
//  Rect Blur
///////////////////////////////////////////////////////////////////////////////

// TODO: it seems like there should be some synergy with SkBlurMask::ComputeBlurProfile
SkBitmap CreateIntegralTable(int width) { … }

int ComputeIntegralTableWidth(float sixSigma) { … }

///////////////////////////////////////////////////////////////////////////////
//  Circle Blur
///////////////////////////////////////////////////////////////////////////////

// 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) { … }

// 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) { … }

// Applies the 1D half kernel vertically at points along the x axis to a circle centered at the
// origin with radius circleR.
static void apply_kernel_in_y(float* results,
                              int numSteps,
                              float firstX,
                              float circleR,
                              int halfKernelSize,
                              const float* summedHalfKernelTable) { … }

// 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) { … }

// 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.
SkBitmap CreateCircleProfile(float sigma, float radius, int profileWidth) { … }

SkBitmap CreateHalfPlaneProfile(int profileWidth) { … }

///////////////////////////////////////////////////////////////////////////////
//  RRect Blur
///////////////////////////////////////////////////////////////////////////////

// Evaluate the vertical blur at the specified 'y' value given the location of the top of the
// rrect.
static uint8_t eval_V(float top, int y, const uint8_t* integral, int integralSize, float sixSigma) { … }

// Apply a gaussian 'kernel' horizontally at the specified 'x', 'y' location.
static uint8_t eval_H(int x,
                      int y,
                      const std::vector<float>& topVec,
                      const float* kernel,
                      int kernelSize,
                      const uint8_t* integral,
                      int integralSize,
                      float sixSigma) { … }

SkBitmap CreateRRectBlurMask(const SkRRect& rrectToDraw, const SkISize& dimensions, float sigma) { … }

} // namespace skgpu