63 lines
2.4 KiB
C
63 lines
2.4 KiB
C
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/*
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* Copyright 2014 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef GrXferProcessor_DEFINED
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#define GrXferProcessor_DEFINED
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#include "GrColor.h"
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#include "GrFragmentProcessor.h"
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#include "GrTypes.h"
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#include "SkXfermode.h"
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/**
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* GrXferProcessor is responsible for implementing the xfer mode that blends the src color and dst
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* color. It does this by emitting fragment shader code and controlling the fixed-function blend
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* state. The inputs to its shader code are the final computed src color and fractional pixel
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* coverage. The GrXferProcessor's shader code writes the fragment shader output color that goes
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* into the fixed-function blend. When dual-source blending is available, it may also write a
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* seconday fragment shader output color. When allowed by the backend API, the GrXferProcessor may
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* read the destination color. The GrXferProcessor is responsible for setting the blend coefficients
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* and blend constant color.
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*
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* A GrXferProcessor is never installed directly into our draw state, but instead is created from a
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* GrXPFactory once we have finalized the state of our draw.
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*/
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class GrXferProcessor : public GrFragmentProcessor {
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private:
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typedef GrFragmentProcessor INHERITED;
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};
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/**
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* We install a GrXPFactory (XPF) early on in the pipeline before all the final draw information is
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* known (e.g. whether there is fractional pixel coverage, will coverage be 1 or 4 channel, is the
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* draw opaque, etc.). Once the state of the draw is finalized, we use the XPF along with all the
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* draw information to create a GrXferProcessor (XP) which can implement the desired blending for
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* the draw.
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*
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* Before the XP is created, the XPF is able to answer queries about what functionality the XPs it
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* creates will have. For example, can it create an XP that supports RGB coverage or will the XP
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* blend with the destination color.
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*/
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class GrXPFactory : public GrProgramElement {
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public:
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virtual const GrXferProcessor* createXferProcessor() const = 0;
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/**
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* This function returns true if the GrXferProcessor generated from this factory will be able to
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* correctly blend when using RGB coverage. The knownColor and knownColorFlags represent the
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* final computed color from the color stages.
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*/
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virtual bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const = 0;
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private:
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typedef GrProgramElement INHERITED;
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};
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#endif
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