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* Copyright 2017 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkShaderBase_DEFINED
#define SkShaderBase_DEFINED
#include "include/core/SkFilterQuality.h"
#include "include/core/SkMatrix.h"
#include "include/core/SkShader.h"
#include "include/private/SkNoncopyable.h"
#include "src/core/SkEffectPriv.h"
#include "src/core/SkMask.h"
#include "src/core/SkTLazy.h"
#include "src/core/SkVM_fwd.h"
#include "src/gpu/GrFPArgs.h"
class GrFragmentProcessor;
class SkArenaAlloc;
class SkColorSpace;
class SkImage;
struct SkImageInfo;
class SkPaint;
class SkRasterPipeline;
class SkRuntimeEffect;
* Shaders can optionally return a subclass of this when appending their stages.
* Doing so tells the caller that the stages can be reused with different CTMs (but nothing
* else can change), by calling the updater's udpate() method before each use.
* This can be a perf-win bulk draws like drawAtlas and drawVertices, where most of the setup
* (i.e. uniforms) are constant, and only something small is changing (i.e. matrices). This
* reuse skips the cost of computing the stages (and/or avoids having to allocate a separate
* shader for each small draw.
class SkStageUpdater {
virtual ~SkStageUpdater() {}
virtual bool SK_WARN_UNUSED_RESULT update(const SkMatrix& ctm, const SkMatrix* localM) = 0;
class SkShaderBase : public SkShader {
~SkShaderBase() override;
sk_sp<SkShader> makeInvertAlpha() const;
sk_sp<SkShader> makeWithCTM(const SkMatrix&) const; // owns its own ctm
* Returns true if the shader is guaranteed to produce only a single color.
* Subclasses can override this to allow loop-hoisting optimization.
virtual bool isConstant() const { return false; }
const SkMatrix& getLocalMatrix() const { return fLocalMatrix; }
enum Flags {
//!< set if all of the colors will be opaque
kOpaqueAlpha_Flag = 1 << 0,
/** set if the spans only vary in X (const in Y).
e.g. an Nx1 bitmap that is being tiled in Y, or a linear-gradient
that varies from left-to-right. This flag specifies this for
kConstInY32_Flag = 1 << 1,
/** hint for the blitter that 4f is the preferred shading mode.
kPrefers4f_Flag = 1 << 2,
* ContextRec acts as a parameter bundle for creating Contexts.
struct ContextRec {
ContextRec(const SkPaint& paint, const SkMatrix& matrix, const SkMatrix* localM,
SkColorType dstColorType, SkColorSpace* dstColorSpace)
: fPaint(&paint)
, fMatrix(&matrix)
, fLocalMatrix(localM)
, fDstColorType(dstColorType)
, fDstColorSpace(dstColorSpace) {}
const SkPaint* fPaint; // the current paint associated with the draw
const SkMatrix* fMatrix; // the current matrix in the canvas
const SkMatrix* fLocalMatrix; // optional local matrix
SkColorType fDstColorType; // the color type of the dest surface
SkColorSpace* fDstColorSpace; // the color space of the dest surface (if any)
bool isLegacyCompatible(SkColorSpace* shadersColorSpace) const;
class Context : public ::SkNoncopyable {
Context(const SkShaderBase& shader, const ContextRec&);
virtual ~Context();
* Called sometimes before drawing with this shader. Return the type of
* alpha your shader will return. The default implementation returns 0.
* Your subclass should override if it can (even sometimes) report a
* non-zero value, since that will enable various blitters to perform
* faster.
virtual uint32_t getFlags() const { return 0; }
* Called for each span of the object being drawn. Your subclass should
* set the appropriate colors (with premultiplied alpha) that correspond
* to the specified device coordinates.
virtual void shadeSpan(int x, int y, SkPMColor[], int count) = 0;
// Reference to shader, so we don't have to dupe information.
const SkShaderBase& fShader;
uint8_t getPaintAlpha() const { return fPaintAlpha; }
const SkMatrix& getTotalInverse() const { return fTotalInverse; }
const SkMatrix& getCTM() const { return fCTM; }
SkMatrix fCTM;
SkMatrix fTotalInverse;
uint8_t fPaintAlpha;
using INHERITED = SkNoncopyable;
* Make a context using the memory provided by the arena.
* @return pointer to context or nullptr if can't be created
Context* makeContext(const ContextRec&, SkArenaAlloc*) const;
* Returns a GrFragmentProcessor that implements the shader for the GPU backend. nullptr is
* returned if there is no GPU implementation.
* The GPU device does not call SkShader::createContext(), instead we pass the view matrix,
* local matrix, and filter quality directly.
* The GrRecordingContext may be used by the to create textures that are required by the
* returned processor.
* The returned GrFragmentProcessor should expect an unpremultiplied input color and
* produce a premultiplied output.
virtual std::unique_ptr<GrFragmentProcessor> asFragmentProcessor(const GrFPArgs&) const;
* If the shader can represent its "average" luminance in a single color, return true and
* if color is not NULL, return that color. If it cannot, return false and ignore the color
* parameter.
* Note: if this returns true, the returned color will always be opaque, as only the RGB
* components are used to compute luminance.
bool asLuminanceColor(SkColor*) const;
// If this returns false, then we draw nothing (do not fall back to shader context)
bool appendStages(const SkStageRec&) const;
bool SK_WARN_UNUSED_RESULT computeTotalInverse(const SkMatrix& ctm,
const SkMatrix* outerLocalMatrix,
SkMatrix* totalInverse) const;
// Returns the total local matrix for this shader:
// M = postLocalMatrix x shaderLocalMatrix x preLocalMatrix
SkTCopyOnFirstWrite<SkMatrix> totalLocalMatrix(const SkMatrix* preLocalMatrix) const;
virtual SkImage* onIsAImage(SkMatrix*, SkTileMode[2]) const {
return nullptr;
virtual SkRuntimeEffect* asRuntimeEffect() const { return nullptr; }
static Type GetFlattenableType() { return kSkShaderBase_Type; }
Type getFlattenableType() const override { return GetFlattenableType(); }
static sk_sp<SkShaderBase> Deserialize(const void* data, size_t size,
const SkDeserialProcs* procs = nullptr) {
return sk_sp<SkShaderBase>(static_cast<SkShaderBase*>(
SkFlattenable::Deserialize(GetFlattenableType(), data, size, procs).release()));
static void RegisterFlattenables();
* If this shader can be represented by another shader + a localMatrix, return that shader and
* the localMatrix. If not, return nullptr and ignore the localMatrix parameter.
virtual sk_sp<SkShader> makeAsALocalMatrixShader(SkMatrix* localMatrix) const;
SkStageUpdater* appendUpdatableStages(const SkStageRec& rec) const {
return this->onAppendUpdatableStages(rec);
skvm::Color program(skvm::Builder*, skvm::Coord device, skvm::Coord local, skvm::Color paint,
const SkMatrixProvider&, const SkMatrix* localM,
SkFilterQuality quality, const SkColorInfo& dst,
skvm::Uniforms* uniforms, SkArenaAlloc* alloc) const;
SkShaderBase(const SkMatrix* localMatrix = nullptr);
void flatten(SkWriteBuffer&) const override;
* Specialize creating a SkShader context using the supplied allocator.
* @return pointer to context owned by the arena allocator.
virtual Context* onMakeContext(const ContextRec&, SkArenaAlloc*) const {
return nullptr;
virtual bool onAsLuminanceColor(SkColor*) const {
return false;
// Default impl creates shadercontext and calls that (not very efficient)
virtual bool onAppendStages(const SkStageRec&) const;
virtual SkStageUpdater* onAppendUpdatableStages(const SkStageRec&) const { return nullptr; }
static skvm::Coord ApplyMatrix(skvm::Builder*, const SkMatrix&, skvm::Coord, skvm::Uniforms*);
// This is essentially const, but not officially so it can be modified in constructors.
SkMatrix fLocalMatrix;
virtual skvm::Color onProgram(skvm::Builder*,
skvm::Coord device, skvm::Coord local, skvm::Color paint,
const SkMatrixProvider&, const SkMatrix* localM,
SkFilterQuality quality, const SkColorInfo& dst,
skvm::Uniforms* uniforms, SkArenaAlloc* alloc) const = 0;
using INHERITED = SkShader;
inline SkShaderBase* as_SB(SkShader* shader) {
return static_cast<SkShaderBase*>(shader);
inline const SkShaderBase* as_SB(const SkShader* shader) {
return static_cast<const SkShaderBase*>(shader);
inline const SkShaderBase* as_SB(const sk_sp<SkShader>& shader) {
return static_cast<SkShaderBase*>(shader.get());
#endif // SkShaderBase_DEFINED