SkGradientBaseShader.cpp | Explore in Territory

/*
 * Copyright 2022 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "src/shaders/gradients/SkGradientBaseShader.h"

#include "include/core/SkAlphaType.h"
#include "include/core/SkColor.h"
#include "include/core/SkColorSpace.h"
#include "include/core/SkColorType.h"
#include "include/core/SkData.h"
#include "include/core/SkImageInfo.h"
#include "include/core/SkShader.h"
#include "include/core/SkTileMode.h"
#include "include/private/SkColorData.h"
#include "include/private/base/SkFloatingPoint.h"
#include "include/private/base/SkMalloc.h"
#include "include/private/base/SkTArray.h"
#include "include/private/base/SkTPin.h"
#include "include/private/base/SkTo.h"
#include "src/base/SkArenaAlloc.h"
#include "src/base/SkFloatBits.h"
#include "src/base/SkVx.h"
#include "src/core/SkColorSpacePriv.h"
#include "src/core/SkColorSpaceXformSteps.h"
#include "src/core/SkConvertPixels.h"
#include "src/core/SkEffectPriv.h"
#include "src/core/SkPicturePriv.h"
#include "src/core/SkRasterPipeline.h"
#include "src/core/SkRasterPipelineOpContexts.h"
#include "src/core/SkRasterPipelineOpList.h"
#include "src/core/SkReadBuffer.h"
#include "src/core/SkWriteBuffer.h"

#include <algorithm>
#include <cmath>
#include <optional>
#include <utility>

usingnamespaceskia_private;

enum GradientSerializationFlags { … };

SkGradientBaseShader::Descriptor::Descriptor() { … }
SkGradientBaseShader::Descriptor::~Descriptor() = default;

void SkGradientBaseShader::flatten(SkWriteBuffer& buffer) const { … }

template <int N, typename T, bool MEM_MOVE>
static bool validate_array(SkReadBuffer& buffer, size_t count, STArray<N, T, MEM_MOVE>* array) { … }

bool SkGradientBaseShader::DescriptorScope::unflatten(SkReadBuffer& buffer,
                                                      SkMatrix* legacyLocalMatrix) { … }

////////////////////////////////////////////////////////////////////////////////////////////

SkGradientBaseShader::SkGradientBaseShader(const Descriptor& desc, const SkMatrix& ptsToUnit)
        : … { … }

SkGradientBaseShader::~SkGradientBaseShader() { … }

static void add_stop_color(SkRasterPipeline_GradientCtx* ctx,
                           size_t stop,
                           SkPMColor4f Fs,
                           SkPMColor4f Bs) { … }

static void add_const_color(SkRasterPipeline_GradientCtx* ctx, size_t stop, SkPMColor4f color) { … }

// Calculate a factor F and a bias B so that color = F*t + B when t is in range of
// the stop. Assume that the distance between stops is 1/gapCount.
static void init_stop_evenly(SkRasterPipeline_GradientCtx* ctx,
                             float gapCount,
                             size_t stop,
                             SkPMColor4f c_l,
                             SkPMColor4f c_r) { … }

// For each stop we calculate a bias B and a scale factor F, such that
// for any t between stops n and n+1, the color we want is B[n] + F[n]*t.
static void init_stop_pos(SkRasterPipeline_GradientCtx* ctx,
                          size_t stop,
                          float t_l,
                          float c_scale,
                          SkPMColor4f c_l,
                          SkPMColor4f c_r) { … }

void SkGradientBaseShader::AppendGradientFillStages(SkRasterPipeline* p,
                                                    SkArenaAlloc* alloc,
                                                    const SkPMColor4f* pmColors,
                                                    const SkScalar* positions,
                                                    int count) { … }

void SkGradientBaseShader::AppendInterpolatedToDstStages(SkRasterPipeline* p,
                                                         SkArenaAlloc* alloc,
                                                         bool colorsAreOpaque,
                                                         const Interpolation& interpolation,
                                                         const SkColorSpace* intermediateColorSpace,
                                                         const SkColorSpace* dstColorSpace) { … }

bool SkGradientBaseShader::appendStages(const SkStageRec& rec,
                                        const SkShaders::MatrixRec& mRec) const { … }

bool SkGradientBaseShader::isOpaque() const { … }

bool SkGradientBaseShader::onAsLuminanceColor(SkColor4f* lum) const { … }

static sk_sp<SkColorSpace> intermediate_color_space(SkGradientShader::Interpolation::ColorSpace cs,
                                                    SkColorSpace* dst) { … }

ConvertColorProc;
PremulColorProc;

static SkPMColor4f srgb_to_hsl(SkPMColor4f rgb, bool* hueIsPowerless) { … }

static SkPMColor4f srgb_to_hwb(SkPMColor4f rgb, bool* hueIsPowerless) { … }

static SkPMColor4f xyzd50_to_lab(SkPMColor4f xyz, bool* /*hueIsPowerless*/) { … }

// The color space is technically LCH, but we produce HCL, so that all polar spaces have hue in the
// first component. This simplifies the hue handling for HueMethod and premul/unpremul.
static SkPMColor4f xyzd50_to_hcl(SkPMColor4f xyz, bool* hueIsPowerless) { … }

// https://bottosson.github.io/posts/oklab/#converting-from-linear-srgb-to-oklab
static SkPMColor4f lin_srgb_to_oklab(SkPMColor4f rgb, bool* /*hueIsPowerless*/) { … }

// The color space is technically OkLCH, but we produce HCL, so that all polar spaces have hue in
// the first component. This simplifies the hue handling for HueMethod and premul/unpremul.
static SkPMColor4f lin_srgb_to_okhcl(SkPMColor4f rgb, bool* hueIsPowerless) { … }

static SkPMColor4f premul_polar(SkPMColor4f hsl) { … }

static SkPMColor4f premul_rgb(SkPMColor4f rgb) { … }

static bool color_space_is_polar(SkGradientShader::Interpolation::ColorSpace cs) { … }

// Given `colors` in `src` color space, an interpolation space, and a `dst` color space,
// we are doing several things. First, some definitions:
//
// The interpolation color space is "special" if it can't be represented as an SkColorSpace. This
// applies to any color space that isn't an RGB space, like Lab or HSL. These need special handling
// because we have to run bespoke code to do the conversion (before interpolation here, and after
// interpolation in the backend shader/pipeline).
//
// The interpolation color space is "polar" if it involves hue (HSL, HWB, LCH, Oklch). These need
// special handling, becuase hue is never premultiplied, and because HueMethod comes into play.
//
// 1) Pick an `intermediate` SkColorSpace. If the interpolation color space is not "special",
//    (kDestination, kSRGB, etc... ), then `intermediate` is exact. Otherwise, `intermediate` is the
//    RGB space that prepares us to do the final conversion. For example, conversion to Lab starts
//    with XYZD50, so `intermediate` will be XYZD50 if we're actually interpolating in Lab.
// 2) Transform all colors to the `intermediate` color space, leaving them unpremultiplied.
// 3) If the interpolation color space is "special", transform the colors to that space.
// 4) If the interpolation color space is "polar", adjust the angles to respect HueMethod.
// 5) If premul interpolation is requested, apply that. For "polar" interpolated colors, don't
//    premultiply hue, only the other two channels. Note that there are four polar spaces.
//    Two have hue as the first component, and two have it as the third component. To reduce
//    complexity, we always store hue in the first component, swapping it with luminance for
//    LCH and Oklch. The backend code (eg, shaders) needs to know about this.
SkColor4fXformer::SkColor4fXformer(const SkGradientBaseShader* shader,
                                   SkColorSpace* dst,
                                   bool forceExplicitPositions) { … }

SkColorConverter::SkColorConverter(const SkColor* colors, int count) { … }

void SkGradientBaseShader::commonAsAGradient(GradientInfo* info) const { … }

// Return true if these parameters are valid/legal/safe to construct a gradient
//
bool SkGradientBaseShader::ValidGradient(const SkColor4f colors[],
                                         int count,
                                         SkTileMode tileMode,
                                         const Interpolation& interpolation) { … }

SkGradientBaseShader::Descriptor::Descriptor(const SkColor4f colors[],
                                             sk_sp<SkColorSpace> colorSpace,
                                             const SkScalar positions[],
                                             int colorCount,
                                             SkTileMode mode,
                                             const Interpolation& interpolation)
        : … { … }

static SkColor4f average_gradient_color(const SkColor4f colors[],
                                        const SkScalar pos[],
                                        int colorCount) { … }

// Except for special circumstances of clamped gradients, every gradient shape--when degenerate--
// can be mapped to the same fallbacks. The specific shape factories must account for special
// clamped conditions separately, this will always return the last color for clamped gradients.
sk_sp<SkShader> SkGradientBaseShader::MakeDegenerateGradient(const SkColor4f colors[],
                                                             const SkScalar pos[],
                                                             int colorCount,
                                                             sk_sp<SkColorSpace> colorSpace,
                                                             SkTileMode mode) { … }
chromium/third_party/skia/src/shaders/gradients/SkGradientBaseShader.cpp
