/* | |

* Copyright 2023 Google LLC | |

* | |

* Use of this source code is governed by a BSD-style license that can be | |

* found in the LICENSE file. | |

*/ | |

#ifndef skgpu_BlurUtils_DEFINED | |

#define skgpu_BlurUtils_DEFINED | |

#include "include/core/SkSize.h" | |

#include "include/core/SkSpan.h" | |

#include "include/private/base/SkFloatingPoint.h" | |

#include <array> | |

class SkRuntimeEffect; | |

struct SkV4; | |

// TODO(b/): Many of these utilities could be lifted even into src/core as part of the backend | |

// agnostic blur engine once that API exists. | |

namespace skgpu { | |

// The kernel width of a Gaussian blur of the given pixel radius, for when all pixels are sampled. | |

constexpr int BlurKernelWidth(int radius) { return 2 * radius + 1; } | |

// The kernel width of a Gaussian blur of the given pixel radius, that relies on HW bilinear | |

// filtering to combine adjacent pixels. | |

constexpr int BlurLinearKernelWidth(int radius) { return radius + 1; } | |

// Any sigmas smaller than this are effectively an identity blur so can skip convolution at a higher | |

// level. The value was chosen because it corresponds roughly to a radius of 1/10px, and because | |

// 2*sigma^2 is slightly greater than SK_ScalarNearlyZero. | |

constexpr bool BlurIsEffectivelyIdentity(float sigma) { return sigma <= 0.03f; } | |

// Convert from a sigma Gaussian standard deviation to a pixel radius such that pixels outside the | |

// radius would have an insignificant contribution to the final blurred value. | |

inline int BlurSigmaRadius(float sigma) { | |

// sk_float_ceil is not constexpr | |

return BlurIsEffectivelyIdentity(sigma) ? 0 : sk_float_ceil2int(3.f * sigma); | |

} | |

// The maximum sigma that can be computed without downscaling is based on the number of uniforms and | |

// texture samples the effects will make in a single pass. For 1D passes, the number of samples | |

// is equal to `BlurLinearKernelWidth`; for 2D passes, it is equal to | |

// `BlurKernelWidth(radiusX)*BlurKernelWidth(radiusY)`. This maps back to different maximum sigmas | |

// depending on the approach used, as well as the ratio between the sigmas for the X and Y axes if | |

// a 2D blur is performed. | |

static constexpr int kMaxBlurSamples = 28; | |

// TODO(b/297393474): Update max linear sigma to 9; it had been 4 when a full 1D kernel was used, | |

// but never updated after the linear filtering optimization reduced the number of sample() calls | |

// required. Keep it at 4 for now to better isolate performance changes due to switching to a | |

// runtime effect and constant loop structure. | |

static constexpr float kMaxLinearBlurSigma = 4.f; // -> radius = 27 -> linear kernel width = 28 | |

// NOTE: There is no defined kMaxBlurSigma for direct 2D blurs since it is entirely dependent on the | |

// ratio between the two axes' sigmas, but generally it will be small on the order of a 5x5 kernel. | |

// Return a runtime effect that applies a 2D Gaussian blur in a single pass. The returned effect can | |

// perform arbitrarily sized blur kernels so long as the kernel area is less than kMaxBlurSamples. | |

// An SkRuntimeEffect is returned to give flexibility for callers to convert it to an SkShader or | |

// a GrFragmentProcessor. Callers are responsible for providing the uniform values (using the | |

// appropriate API of the target effect type). The effect declares the following uniforms: | |

// | |

// uniform half4 kernel[7]; | |

// uniform half4 offsets[14]; | |

// uniform shader child; | |

// | |

// 'kernel' should be set to the output of Compute2DBlurKernel(). 'offsets' should be set to the | |

// output of Compute2DBlurOffsets() with the same 'radii' passed to this function. 'child' should be | |

// bound to whatever input is intended to be blurred, and can use nearest-neighbor sampling | |

// (assuming it's an image). | |

const SkRuntimeEffect* GetBlur2DEffect(const SkISize& radii); | |

// Return a runtime effect that applies a 1D Gaussian blur, taking advantage of HW linear | |

// interpolation to accumulate adjacent pixels with fewer samples. The returned effect can be used | |

// for both X and Y axes by changing the 'dir' uniform value (see below). It can be used for all | |

// 1D blurs such that BlurLinearKernelWidth(radius) is less than or equal to kMaxBlurSamples. | |

// Like GetBlur2DEffect(), the caller is free to convert this to an SkShader or a | |

// GrFragmentProcessor and is responsible for assigning uniforms with the appropriate API. Its | |

// uniforms are declared as: | |

// | |

// uniform half4 offsetsAndKernel[14]; | |

// uniform half2 dir; | |

// uniform int radius; | |

// uniform shader child; | |

// | |

// 'offsetsAndKernel' should be set to the output of Compute1DBlurLinearKernel(). 'radius' should | |

// match the radius passed to that function. 'dir' should either be the vector {1,0} or {0,1} | |

// for X and Y axis passes, respectively. 'child' should be bound to whatever input is intended to | |

// be blurred and must use linear sampling in order for the outer blur effect to function correctly. | |

const SkRuntimeEffect* GetLinearBlur1DEffect(int radius); | |

// Calculates a set of weights for a 2D Gaussian blur of the given sigma and radius. It is assumed | |

// that the radius was from prior calls to BlurSigmaRadius(sigma.width()|height()) and is passed in | |

// to avoid redundant calculations. | |

// | |

// The provided span is fully written. The kernel is stored in row-major order based on the provided | |

// radius. Any remaining indices in the span are zero initialized. The span must have at least | |

// BlurKernelWidth(radius.width())*BlurKernelWidth(radius.height()) elements. | |

// | |

// NOTE: These take spans because it can be useful to compute full kernels that are larger than what | |

// is supported in the GPU effects. | |

void Compute2DBlurKernel(SkSize sigma, | |

SkISize radius, | |

SkSpan<float> kernel); | |

// A convenience function that packs the kMaxBlurSample scalars into SkV4's to match the required | |

// type of the uniforms in GetBlur2DEffect(). | |

void Compute2DBlurKernel(SkSize sigma, | |

SkISize radius, | |

std::array<SkV4, kMaxBlurSamples/4>& kernel); | |

// A convenience for the 2D case where one dimension has a sigma of 0. | |

inline void Compute1DBlurKernel(float sigma, int radius, SkSpan<float> kernel) { | |

Compute2DBlurKernel(SkSize{sigma, 0.f}, SkISize{radius, 0}, kernel); | |

} | |

// Utility function to fill in 'offsets' for the effect returned by GetBlur2DEffect(). It | |

// automatically fills in the elements beyond the kernel size with the last real offset to | |

// maximize texture cache hits. Each offset is really an SkV2 but are packed into SkV4's to match | |

// the uniform declaration, and are otherwise ordered row-major. | |

void Compute2DBlurOffsets(SkISize radius, std::array<SkV4, kMaxBlurSamples/2>& offsets); | |

// Calculates a set of weights and sampling offsets for a 1D blur that uses GPU hardware to linearly | |

// combine two logical source pixel values. This assumes that 'radius' was from a prior call to | |

// BlurSigmaRadius() and is passed in to avoid redundant calculations. To match std140 uniform | |

// packing, the offset and kernel weight for adjacent samples are packed into a single SkV4 as | |

// {offset[2*i], kernel[2*i], offset[2*i+1], kernel[2*i+1]} | |

// | |

// The provided array is fully written to. The calculated values are written to indices 0 through | |

// BlurLinearKernelWidth(radius), with any remaining indices zero initialized. It requires the spans | |

// to be the same size and have at least BlurLinearKernelWidth(radius) elements. | |

// | |

// NOTE: This takes an array of a constrained size because its main use is calculating uniforms for | |

// an effect with a matching constraint. Knowing the size of the linear kernel means the full kernel | |

// can be stored on the stack internally. | |

void Compute1DBlurLinearKernel(float sigma, | |

int radius, | |

std::array<SkV4, kMaxBlurSamples/2>& offsetsAndKernel); | |

} // namespace skgpu | |

#endif // skgpu_BlurUtils_DEFINED |