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/*
* Copyright 2014 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef GrXferProcessor_DEFINED
#define GrXferProcessor_DEFINED
#include "GrColor.h"
#include "GrFragmentProcessor.h"
#include "GrTypes.h"
#include "SkXfermode.h"
/**
* GrXferProcessor is responsible for implementing the xfer mode that blends the src color and dst
* color. It does this by emitting fragment shader code and controlling the fixed-function blend
* state. The inputs to its shader code are the final computed src color and fractional pixel
* coverage. The GrXferProcessor's shader code writes the fragment shader output color that goes
* into the fixed-function blend. When dual-source blending is available, it may also write a
* seconday fragment shader output color. When allowed by the backend API, the GrXferProcessor may
* read the destination color. The GrXferProcessor is responsible for setting the blend coefficients
* and blend constant color.
*
* A GrXferProcessor is never installed directly into our draw state, but instead is created from a
* GrXPFactory once we have finalized the state of our draw.
*/
class GrXferProcessor : public GrFragmentProcessor {
private:
typedef GrFragmentProcessor INHERITED;
};
/**
* We install a GrXPFactory (XPF) early on in the pipeline before all the final draw information is
* known (e.g. whether there is fractional pixel coverage, will coverage be 1 or 4 channel, is the
* draw opaque, etc.). Once the state of the draw is finalized, we use the XPF along with all the
* draw information to create a GrXferProcessor (XP) which can implement the desired blending for
* the draw.
*
* Before the XP is created, the XPF is able to answer queries about what functionality the XPs it
* creates will have. For example, can it create an XP that supports RGB coverage or will the XP
* blend with the destination color.
*/
class GrXPFactory : public SkRefCnt {
public:
virtual const GrXferProcessor* createXferProcessor() const = 0;
/**
* This function returns true if the GrXferProcessor generated from this factory will be able to
* correctly blend when using RGB coverage. The knownColor and knownColorFlags represent the
* final computed color from the color stages.
*/
virtual bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const = 0;
bool isEqual(const GrXPFactory& that) const {
if (this->classID() != that.classID()) {
return false;
}
return this->onIsEqual(that);
}
/**
* Helper for down-casting to a GrXPFactory subclass
*/
template <typename T> const T& cast() const { return *static_cast<const T*>(this); }
uint32_t classID() const { SkASSERT(kIllegalXPFClassID != fClassID); return fClassID; }
protected:
GrXPFactory() : fClassID(kIllegalXPFClassID) {}
template <typename XPF_SUBCLASS> void initClassID() {
static uint32_t kClassID = GenClassID();
fClassID = kClassID;
}
uint32_t fClassID;
private:
virtual bool onIsEqual(const GrXPFactory&) const = 0;
static uint32_t GenClassID() {
// fCurrXPFactoryID has been initialized to kIllegalXPFactoryID. The
// atomic inc returns the old value not the incremented value. So we add
// 1 to the returned value.
uint32_t id = static_cast<uint32_t>(sk_atomic_inc(&gCurrXPFClassID)) + 1;
if (!id) {
SkFAIL("This should never wrap as it should only be called once for each GrXPFactory "
"subclass.");
}
return id;
}
enum {
kIllegalXPFClassID = 0,
};
static int32_t gCurrXPFClassID;
typedef GrProgramElement INHERITED;
};
#endif
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