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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 "SkFilterQuality.h"
#include "SkMatrix.h"
#include "SkShader.h"
class GrContext;
class GrFragmentProcessor;
class SkArenaAlloc;
class SkColorSpace;
class SkColorSpaceXformer;
class SkImage;
struct SkImageInfo;
class SkPaint;
class SkRasterPipeline;
class SkShaderBase : public SkShader {
~SkShaderBase() override;
* 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 {
enum DstType {
kPMColor_DstType, // clients prefer shading into PMColor dest
kPM4f_DstType, // clients prefer shading into PM4f dest
ContextRec(const SkPaint& paint, const SkMatrix& matrix, const SkMatrix* localM,
DstType dstType, SkColorSpace* dstColorSpace)
: fPaint(&paint)
, fMatrix(&matrix)
, fLocalMatrix(localM)
, fPreferredDstType(dstType)
, 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
const DstType fPreferredDstType; // the "natural" client dest type
SkColorSpace* fDstColorSpace; // the color space of the dest surface (if any)
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;
virtual void shadeSpan4f(int x, int y, SkPM4f[], int count);
* The const void* ctx is only const because all the implementations are const.
* This can be changed to non-const if a new shade proc needs to change the ctx.
typedef void (*ShadeProc)(const void* ctx, int x, int y, SkPMColor[], int count);
virtual ShadeProc asAShadeProc(void** ctx);
* Similar to shadeSpan, but only returns the alpha-channel for a span.
* The default implementation calls shadeSpan() and then extracts the alpha
* values from the returned colors.
virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);
// Notification from blitter::blitMask in case we need to see the non-alpha channels
virtual void set3DMask(const SkMask*) {}
// 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;
typedef SkNoncopyable INHERITED;
* 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;
* Shaders may opt-in for burst mode, if they can operate
* significantly more efficiently in that mode.
* Burst mode is prioritized in SkRasterPipelineBlitter over
* regular (appendStages) pipeline operation.
Context* makeBurstPipelineContext(const ContextRec&, SkArenaAlloc*) const;
struct AsFPArgs {
AsFPArgs() {}
AsFPArgs(GrContext* context,
const SkMatrix* viewMatrix,
const SkMatrix* localMatrix,
SkFilterQuality filterQuality,
SkColorSpace* dstColorSpace)
: fContext(context)
, fViewMatrix(viewMatrix)
, fLocalMatrix(localMatrix)
, fFilterQuality(filterQuality)
, fDstColorSpace(dstColorSpace) {}
GrContext* fContext;
const SkMatrix* fViewMatrix;
const SkMatrix* fLocalMatrix;
SkFilterQuality fFilterQuality;
SkColorSpace* fDstColorSpace;
* Returns a GrFragmentProcessor that implements the shader for the GPU backend. NULL 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 GrContext 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 sk_sp<GrFragmentProcessor> asFragmentProcessor(const AsFPArgs&) 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;
* Returns a shader transformed into a new color space via the |xformer|.
sk_sp<SkShader> makeColorSpace(SkColorSpaceXformer* xformer) const {
return this->onMakeColorSpace(xformer);
bool isRasterPipelineOnly() const {
// We always use RP when perspective is present.
return fLocalMatrix.hasPerspective() || this->onIsRasterPipelineOnly();
// If this returns false, then we draw nothing (do not fall back to shader context)
bool appendStages(SkRasterPipeline*, SkColorSpace* dstCS, SkArenaAlloc*,
const SkMatrix& ctm, const SkPaint&, const SkMatrix* localM=nullptr) const;
bool computeTotalInverse(const SkMatrix& ctm,
const SkMatrix* outerLocalMatrix,
SkMatrix* totalInverse) const;
virtual bool onIsABitmap(SkBitmap*, SkMatrix*, TileMode[2]) const {
return false;
virtual SkImage* onIsAImage(SkMatrix*, TileMode[2]) const {
return nullptr;
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;
* Overriden by shaders which prefer burst mode.
virtual Context* onMakeBurstPipelineContext(const ContextRec&, SkArenaAlloc*) const {
return nullptr;
virtual bool onAsLuminanceColor(SkColor*) const {
return false;
virtual sk_sp<SkShader> onMakeColorSpace(SkColorSpaceXformer*) const {
return sk_ref_sp(const_cast<SkShaderBase*>(this));
// Default impl creates shadercontext and calls that (not very efficient)
virtual bool onAppendStages(SkRasterPipeline*, SkColorSpace* dstCS, SkArenaAlloc*,
const SkMatrix&, const SkPaint&, const SkMatrix* localM) const;
virtual bool onIsRasterPipelineOnly() const { return false; }
// This is essentially const, but not officially so it can be modified in constructors.
SkMatrix fLocalMatrix;
typedef SkShader INHERITED;
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