skia2/include/gpu/GrProcessor.h

/*
 * Copyright 2012 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrProcessor_DEFINED
#define GrProcessor_DEFINED

#include "GrBackendProcessorFactory.h"
#include "GrColor.h"
#include "GrProcessorUnitTest.h"
#include "GrProgramElement.h"
#include "GrTextureAccess.h"
#include "SkMath.h"

class GrContext;
class GrCoordTransform;

/** Provides custom shader code to the Ganesh shading pipeline. GrProcessor objects *must* be
    immutable: after being constructed, their fields may not change.

    Dynamically allocated GrProcessors are managed by a per-thread memory pool. The ref count of an
    processor must reach 0 before the thread terminates and the pool is destroyed. To create a
    static processor use the helper macro GR_CREATE_STATIC_PROCESSOR declared below.
 */
class GrProcessor : public GrProgramElement {
public:
    SK_DECLARE_INST_COUNT(GrProcessor)

    virtual ~GrProcessor();

    struct InvariantOutput{
        InvariantOutput() : fColor(0), fValidFlags(0), fIsSingleComponent(false),
                            fNonMulStageFound(false), fWillUseInputColor(true) {}

        enum ReadInput {
            kWill_ReadInput,
            kWillNot_ReadInput,
        };

        void mulByUnknownOpaqueColor() {
            if (this->isOpaque()) {
                fValidFlags = kA_GrColorComponentFlag;
                fIsSingleComponent = false;
            } else {
                // Since the current state is not opaque we no longer care if the color being
                // multiplied is opaque.
                this->mulByUnknownColor(); 
            }
        }

        void mulByUnknownColor() {
            if (this->hasZeroAlpha()) {
                this->internalSetToTransparentBlack();
            } else {
                this->internalSetToUnknown();
            }
        }

        void mulByUnknownAlpha() {
            if (this->hasZeroAlpha()) {
                this->internalSetToTransparentBlack();
            } else {
                // We don't need to change fIsSingleComponent in this case
                fValidFlags = 0;
            }
        }

        void mulByKnownAlpha(uint8_t alpha) {
            if (this->hasZeroAlpha() || 0 == alpha) {
                this->internalSetToTransparentBlack();
            } else {
                if (alpha != 255) {
                    // Multiply color by alpha
                    fColor = GrColorPackRGBA(SkMulDiv255Round(GrColorUnpackR(fColor), alpha),
                                             SkMulDiv255Round(GrColorUnpackG(fColor), alpha),
                                             SkMulDiv255Round(GrColorUnpackB(fColor), alpha),
                                             SkMulDiv255Round(GrColorUnpackA(fColor), alpha));
                }
            }
        }

        void invalidateComponents(uint8_t invalidateFlags, ReadInput readsInput) {
            fValidFlags &= ~invalidateFlags;
            fIsSingleComponent = false;
            if (kWillNot_ReadInput == readsInput) {
                fWillUseInputColor = false;
            }
        }

        void setToOther(uint8_t validFlags, GrColor color, ReadInput readsInput) {
            fValidFlags = validFlags;
            fColor = color;
            fIsSingleComponent = false;
            fNonMulStageFound = true;
            if (kWillNot_ReadInput == readsInput) {
                fWillUseInputColor = false;
            }
        }

        void setToUnknown(ReadInput readsInput) {
            this->internalSetToUnknown();
            fNonMulStageFound= true;
            if (kWillNot_ReadInput == readsInput) {
                fWillUseInputColor = false;
            }
        }

        bool isOpaque() const {
            return ((fValidFlags & kA_GrColorComponentFlag) && 0xFF == GrColorUnpackA(fColor));
        }

        bool isSolidWhite() const {
            return (fValidFlags == kRGBA_GrColorComponentFlags && 0xFFFFFFFF == fColor);
        }

        GrColor color() const { return fColor; }
        uint8_t validFlags() const { return fValidFlags; }

        /**
         * If isSingleComponent is true, then the flag values for r, g, b, and a must all be the
         * same. If the flags are all set then all color components must be equal.
         */
        SkDEBUGCODE(void validate() const;)

    private:
        void internalSetToTransparentBlack() {
            fValidFlags = kRGBA_GrColorComponentFlags;
            fColor = 0;
            fIsSingleComponent = true;
        }

        void internalSetToUnknown() {
            fValidFlags = 0;
            fIsSingleComponent = false;
        }

        bool hasZeroAlpha() const {
            return ((fValidFlags & kA_GrColorComponentFlag) && 0 == GrColorUnpackA(fColor));
        }

        SkDEBUGCODE(bool colorComponentsAllEqual() const;)
        /**
         * If alpha is valid, check that any valid R,G,B values are <= A
         */
        SkDEBUGCODE(bool validPreMulColor() const;)

        // Friended class that have "controller" code which loop over stages calling
        // computeInvarianteOutput(). These controllers may need to manually adjust the internal
        // members of InvariantOutput
        friend class GrDrawState;
        friend class GrOptDrawState;
        friend class GrPaint;
        friend class GrProcessor;

        GrColor fColor;
        uint32_t fValidFlags;
        bool fIsSingleComponent;
        bool fNonMulStageFound;
        bool fWillUseInputColor;
    };

    /**
     * This function is used to perform optimizations. When called the invarientOuput param
     * indicate whether the input components to this processor in the FS will have known values.
     * In inout the validFlags member is a bitfield of GrColorComponentFlags. The isSingleComponent
     * member indicates whether the input will be 1 or 4 bytes. The function updates the members of
     * inout to indicate known values of its output. A component of the color member only has
     * meaning if the corresponding bit in validFlags is set.
     */
    void computeInvariantOutput(InvariantOutput* inout) const {
        inout->fWillUseInputColor = true;
        this->onComputeInvariantOutput(inout);
#ifdef SK_DEBUG
        inout->validate();
#endif
    }

    /** This object, besides creating back-end-specific helper objects, is used for run-time-type-
        identification. The factory should be an instance of templated class,
        GrTBackendProcessorFactory. It is templated on the subclass of GrProcessor. The subclass
        must have a nested type (or typedef) named GLProcessor which will be the subclass of
        GrGLProcessor created by the factory.

        Example:
        class MyCustomProcessor : public GrProcessor {
        ...
            virtual const GrBackendProcessorFactory& getFactory() const SK_OVERRIDE {
                return GrTBackendProcessorFactory<MyCustomProcessor>::getInstance();
            }
        ...
        };
     */
    virtual const GrBackendProcessorFactory& getFactory() const = 0;

    /** Human-meaningful string to identify this prcoessor; may be embedded
        in generated shader code. */
    const char* name() const;

    int numTextures() const { return fTextureAccesses.count(); }

    /** Returns the access pattern for the texture at index. index must be valid according to
        numTextures(). */
    const GrTextureAccess& textureAccess(int index) const { return *fTextureAccesses[index]; }

    /** Shortcut for textureAccess(index).texture(); */
    GrTexture* texture(int index) const { return this->textureAccess(index).getTexture(); }

    /** Will this processor read the fragment position? */
    bool willReadFragmentPosition() const { return fWillReadFragmentPosition; }

    void* operator new(size_t size);
    void operator delete(void* target);

    void* operator new(size_t size, void* placement) {
        return ::operator new(size, placement);
    }
    void operator delete(void* target, void* placement) {
        ::operator delete(target, placement);
    }

    /**
      * Helper for down-casting to a GrProcessor subclass
      */
    template <typename T> const T& cast() const { return *static_cast<const T*>(this); }

protected:
    /**
     * Subclasses call this from their constructor to register GrTextureAccesses. The processor
     * subclass manages the lifetime of the accesses (this function only stores a pointer). The
     * GrTextureAccess is typically a member field of the GrProcessor subclass. This must only be
     * called from the constructor because GrProcessors are immutable.
     */
    void addTextureAccess(const GrTextureAccess* textureAccess);

    GrProcessor()
        : fWillReadFragmentPosition(false) {}

    /**
     * If the prcoessor will generate a backend-specific processor that will read the fragment
     * position in the FS then it must call this method from its constructor. Otherwise, the
     * request to access the fragment position will be denied.
     */
    void setWillReadFragmentPosition() { fWillReadFragmentPosition = true; }

    SkDEBUGCODE(void assertTexturesEqual(const GrProcessor& other) const;)

private:

    /** 
     * Subclass implements this to support getConstantColorComponents(...).
     */
    virtual void onComputeInvariantOutput(InvariantOutput* inout) const = 0;

    SkSTArray<4, const GrTextureAccess*, true>   fTextureAccesses;
    bool                                         fWillReadFragmentPosition;

    typedef GrProgramElement INHERITED;
};


/**
 * This creates a processor outside of the memory pool. The processor's destructor will be called
 * at global destruction time. NAME will be the name of the created instance.
 */
#define GR_CREATE_STATIC_PROCESSOR(NAME, PROC_CLASS, ARGS)                                 \
static SkAlignedSStorage<sizeof(PROC_CLASS)> g_##NAME##_Storage;                           \
static PROC_CLASS* NAME SkNEW_PLACEMENT_ARGS(g_##NAME##_Storage.get(), PROC_CLASS, ARGS);  \
static SkAutoTDestroy<GrProcessor> NAME##_ad(NAME);

#endif