src/gpu/GrDrawState.h

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrDrawState_DEFINED
#define GrDrawState_DEFINED


#include "GrBlend.h"
#include "GrDrawTargetCaps.h"
#include "GrGeometryProcessor.h"
#include "GrGpuResourceRef.h"
#include "GrProcessorStage.h"
#include "GrProcOptInfo.h"
#include "GrRenderTarget.h"
#include "GrStencil.h"
#include "SkMatrix.h"
#include "effects/GrSimpleTextureEffect.h"

class GrDrawTargetCaps;
class GrOptDrawState;
class GrPaint;
class GrTexture;

class GrDrawState {
public:
    GrDrawState() {
        SkDEBUGCODE(fBlockEffectRemovalCnt = 0;)
        this->reset();
    }

    GrDrawState(const SkMatrix& initialViewMatrix) {
        SkDEBUGCODE(fBlockEffectRemovalCnt = 0;)
        this->reset(initialViewMatrix);
    }

    /**
     * Copies another draw state.
     **/
    GrDrawState(const GrDrawState& state) {
        SkDEBUGCODE(fBlockEffectRemovalCnt = 0;)
        *this = state;
    }

    /**
     * Copies another draw state with a preconcat to the view matrix.
     **/
    GrDrawState(const GrDrawState& state, const SkMatrix& preConcatMatrix);

    virtual ~GrDrawState();

    /**
     * Resets to the default state. GrProcessors will be removed from all stages.
     */
    void reset() { this->onReset(NULL); }

    void reset(const SkMatrix& initialViewMatrix) { this->onReset(&initialViewMatrix); }

    /**
     * Initializes the GrDrawState based on a GrPaint, view matrix and render target. Note that
     * GrDrawState encompasses more than GrPaint. Aspects of GrDrawState that have no GrPaint
     * equivalents are set to default values with the exception of vertex attribute state which
     * is unmodified by this function and clipping which will be enabled.
     */
    void setFromPaint(const GrPaint& , const SkMatrix& viewMatrix, GrRenderTarget*);

    ///////////////////////////////////////////////////////////////////////////
    /// @name Vertex Attributes
    ////

    enum {
        kMaxVertexAttribCnt = kLast_GrVertexAttribBinding + 4,
    };

    const GrVertexAttrib* getVertexAttribs() const { return fVAPtr; }
    int getVertexAttribCount() const { return fVACount; }

    size_t getVertexStride() const { return fVAStride; }

    bool hasLocalCoordAttribute() const {
        return -1 != fFixedFunctionVertexAttribIndices[kLocalCoord_GrVertexAttribBinding];
    }
    bool hasColorVertexAttribute() const {
        return -1 != fFixedFunctionVertexAttribIndices[kColor_GrVertexAttribBinding];
    }
    bool hasCoverageVertexAttribute() const {
        return -1 != fFixedFunctionVertexAttribIndices[kCoverage_GrVertexAttribBinding];
    }

    const int* getFixedFunctionVertexAttribIndices() const {
        return fFixedFunctionVertexAttribIndices;
    }

    bool validateVertexAttribs() const;

   /**
     * The format of vertices is represented as an array of GrVertexAttribs, with each representing
     * the type of the attribute, its offset, and semantic binding (see GrVertexAttrib in
     * GrTypesPriv.h).
     *
     * The mapping of attributes with kEffect bindings to GrProcessor inputs is specified when
     * setEffect is called.
     */

    /**
     *  Sets vertex attributes for next draw. The object driving the templatization
     *  should be a global GrVertexAttrib array that is never changed.
     *
     *  @param count      the number of attributes being set, limited to kMaxVertexAttribCnt.
     *  @param stride     the number of bytes between successive vertex data.
     */
    template <const GrVertexAttrib A[]> void setVertexAttribs(int count, size_t stride) {
        this->internalSetVertexAttribs(A, count, stride);
    }

    /**
     *  Sets default vertex attributes for next draw. The default is a single attribute:
     *  {kVec2f_GrVertexAttribType, 0, kPosition_GrVertexAttribType}
     */
    void setDefaultVertexAttribs();

    /**
     * Helper to save/restore vertex attribs
     */
     class AutoVertexAttribRestore {
     public:
         AutoVertexAttribRestore(GrDrawState* drawState);

         ~AutoVertexAttribRestore() { fDrawState->internalSetVertexAttribs(fVAPtr, fVACount,
                                                                           fVAStride); }

     private:
         GrDrawState*          fDrawState;
         const GrVertexAttrib* fVAPtr;
         int                   fVACount;
         size_t                fVAStride;
     };

    /// @}

    /**
     * Depending on features available in the underlying 3D API and the color blend mode requested
     * it may or may not be possible to correctly blend with fractional pixel coverage generated by
     * the fragment shader.
     *
     * This function considers the current draw state and the draw target's capabilities to
     * determine whether coverage can be handled correctly. This function assumes that the caller
     * intends to specify fractional pixel coverage (via setCoverage(), through a coverage vertex
     * attribute, or a coverage effect) but may not have specified it yet.
     */
    bool couldApplyCoverage(const GrDrawTargetCaps& caps) const;

    /**
     * Determines whether the output coverage is guaranteed to be one for all pixels hit by a draw.
     */
    bool hasSolidCoverage() const;

    /**
     * This function returns true if the render target destination pixel values will be read for
     * blending during draw.
     */
    bool willBlendWithDst() const;

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name Color
    ////

    GrColor getColor() const { return fColor; }

    /**
     *  Sets color for next draw to a premultiplied-alpha color.
     *
     *  @param color    the color to set.
     */
    void setColor(GrColor color) {
        if (color != fColor) {
            fColor = color;
            fColorProcInfoValid = false;
        }
    }

    /**
     *  Sets the color to be used for the next draw to be
     *  (r,g,b,a) = (alpha, alpha, alpha, alpha).
     *
     *  @param alpha The alpha value to set as the color.
     */
    void setAlpha(uint8_t a) { this->setColor((a << 24) | (a << 16) | (a << 8) | a); }

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name Coverage
    ////

    uint8_t getCoverage() const { return fCoverage; }

    GrColor getCoverageColor() const {
        return GrColorPackRGBA(fCoverage, fCoverage, fCoverage, fCoverage);
    }

    /**
     * Sets a constant fractional coverage to be applied to the draw. The
     * initial value (after construction or reset()) is 0xff. The constant
     * coverage is ignored when per-vertex coverage is provided.
     */
    void setCoverage(uint8_t coverage) {
        if (coverage != fCoverage) {
            fCoverage = coverage;
            fCoverageProcInfoValid = false;
        }
    }

    /// @}

    /**
     * The geometry processor is the sole element of the skia pipeline which can use the vertex,
     * geometry, and tesselation shaders.  The GP may also compute a coverage in its fragment shader
     * but is never put in the color processing pipeline.
     */

    const GrGeometryProcessor* setGeometryProcessor(const GrGeometryProcessor* geometryProcessor) {
        SkASSERT(geometryProcessor);
        SkASSERT(!this->hasGeometryProcessor());
        fGeometryProcessor.reset(SkRef(geometryProcessor));
        fCoverageProcInfoValid = false;
        return geometryProcessor;
    }

    ///////////////////////////////////////////////////////////////////////////
    /// @name Effect Stages
    /// Each stage hosts a GrProcessor. The effect produces an output color or coverage in the
    /// fragment shader. Its inputs are the output from the previous stage as well as some variables
    /// available to it in the fragment and vertex shader (e.g. the vertex position, the dst color,
    /// the fragment position, local coordinates).
    ///
    /// The stages are divided into two sets, color-computing and coverage-computing. The final
    /// color stage produces the final pixel color. The coverage-computing stages function exactly
    /// as the color-computing but the output of the final coverage stage is treated as a fractional
    /// pixel coverage rather than as input to the src/dst color blend step.
    ///
    /// The input color to the first color-stage is either the constant color or interpolated
    /// per-vertex colors. The input to the first coverage stage is either a constant coverage
    /// (usually full-coverage) or interpolated per-vertex coverage.
    ///
    /// See the documentation of kCoverageDrawing_StateBit for information about disabling the
    /// the color / coverage distinction.
    ////

    int numColorStages() const { return fColorStages.count(); }
    int numCoverageStages() const { return fCoverageStages.count(); }
    int numFragmentStages() const { return this->numColorStages() + this->numCoverageStages(); }
    int numTotalStages() const {
         return this->numFragmentStages() + (this->hasGeometryProcessor() ? 1 : 0);
    }

    bool hasGeometryProcessor() const { return SkToBool(fGeometryProcessor.get()); }
    const GrGeometryProcessor* getGeometryProcessor() const { return fGeometryProcessor.get(); }
    const GrFragmentStage& getColorStage(int idx) const { return fColorStages[idx]; }
    const GrFragmentStage& getCoverageStage(int idx) const { return fCoverageStages[idx]; }

    /**
     * Checks whether any of the effects will read the dst pixel color.
     */
    bool willEffectReadDstColor() const;

    const GrFragmentProcessor* addColorProcessor(const GrFragmentProcessor* effect) {
        SkASSERT(effect);
        SkNEW_APPEND_TO_TARRAY(&fColorStages, GrFragmentStage, (effect));
        fColorProcInfoValid = false;
        return effect;
    }

    const GrFragmentProcessor* addCoverageProcessor(const GrFragmentProcessor* effect) {
        SkASSERT(effect);
        SkNEW_APPEND_TO_TARRAY(&fCoverageStages, GrFragmentStage, (effect));
        fCoverageProcInfoValid = false;
        return effect;
    }

    /**
     * Creates a GrSimpleTextureEffect that uses local coords as texture coordinates.
     */
    void addColorTextureProcessor(GrTexture* texture, const SkMatrix& matrix) {
        this->addColorProcessor(GrSimpleTextureEffect::Create(texture, matrix))->unref();
    }

    void addCoverageTextureProcessor(GrTexture* texture, const SkMatrix& matrix) {
        this->addCoverageProcessor(GrSimpleTextureEffect::Create(texture, matrix))->unref();
    }

    void addColorTextureProcessor(GrTexture* texture,
                                  const SkMatrix& matrix,
                                  const GrTextureParams& params) {
        this->addColorProcessor(GrSimpleTextureEffect::Create(texture, matrix, params))->unref();
    }

    void addCoverageTextureProcessor(GrTexture* texture,
                                     const SkMatrix& matrix,
                                     const GrTextureParams& params) {
        this->addCoverageProcessor(GrSimpleTextureEffect::Create(texture, matrix, params))->unref();
    }

    /**
     * When this object is destroyed it will remove any color/coverage effects from the draw state
     * that were added after its constructor.
     *
     * This class has strange behavior around geometry processor. If there is a GP on the draw state
     * it will assert that the GP is not modified until after the destructor of the ARE. If the
     * draw state has a NULL GP when the ARE is constructed then it will reset it to null in the
     * destructor.
     *
     * TODO: We'd prefer for the ARE to just save and restore the GP. However, this would add
     * significant complexity to the multi-ref architecture for deferred drawing. Once GrDrawState
     * and GrOptDrawState are fully separated then GrDrawState will never be in the deferred
     * execution state and GrOptDrawState always will be (and will be immutable and therefore
     * unable to have an ARE). At this point we can restore sanity and have the ARE save and restore
     * the GP.
     */
    class AutoRestoreEffects : public ::SkNoncopyable {
    public:
        AutoRestoreEffects() 
            : fDrawState(NULL)
            , fOriginalGPID(SK_InvalidUniqueID)
            , fColorEffectCnt(0)
            , fCoverageEffectCnt(0) {}

        AutoRestoreEffects(GrDrawState* ds)
            : fDrawState(NULL)
            , fOriginalGPID(SK_InvalidUniqueID)
            , fColorEffectCnt(0)
            , fCoverageEffectCnt(0) {
            this->set(ds);
        }

        ~AutoRestoreEffects() { this->set(NULL); }

        void set(GrDrawState* ds);

        bool isSet() const { return SkToBool(fDrawState); }

    private:
        GrDrawState*    fDrawState;
        uint32_t        fOriginalGPID;
        int             fColorEffectCnt;
        int             fCoverageEffectCnt;
    };

    /**
     * AutoRestoreStencil
     *
     * This simple struct saves and restores the stencil settings
     */
    class AutoRestoreStencil : public ::SkNoncopyable {
    public:
        AutoRestoreStencil() : fDrawState(NULL) {}

        AutoRestoreStencil(GrDrawState* ds) : fDrawState(NULL) { this->set(ds); }

        ~AutoRestoreStencil() { this->set(NULL); }

        void set(GrDrawState* ds) {
            if (fDrawState) {
                fDrawState->setStencil(fStencilSettings);
            }
            fDrawState = ds;
            if (ds) {
                fStencilSettings = ds->getStencil();
            }
        }

        bool isSet() const { return SkToBool(fDrawState); }

    private:
        GrDrawState*       fDrawState;
        GrStencilSettings  fStencilSettings;
    };

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name Blending
    ////

    GrBlendCoeff getSrcBlendCoeff() const { return fSrcBlend; }
    GrBlendCoeff getDstBlendCoeff() const { return fDstBlend; }

    /**
     * Retrieves the last value set by setBlendConstant()
     * @return the blending constant value
     */
    GrColor getBlendConstant() const { return fBlendConstant; }

    /**
     * Determines whether multiplying the computed per-pixel color by the pixel's fractional
     * coverage before the blend will give the correct final destination color. In general it
     * will not as coverage is applied after blending.
     */
    bool canTweakAlphaForCoverage() const;

    /**
     * Sets the blending function coefficients.
     *
     * The blend function will be:
     *    D' = sat(S*srcCoef + D*dstCoef)
     *
     *   where D is the existing destination color, S is the incoming source
     *   color, and D' is the new destination color that will be written. sat()
     *   is the saturation function.
     *
     * @param srcCoef coefficient applied to the src color.
     * @param dstCoef coefficient applied to the dst color.
     */
    void setBlendFunc(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff) {
        if (srcCoeff != fSrcBlend || dstCoeff != fDstBlend) {
            fSrcBlend = srcCoeff;
            fDstBlend = dstCoeff;
        }
    #ifdef SK_DEBUG
        if (GrBlendCoeffRefsDst(dstCoeff)) {
            SkDebugf("Unexpected dst blend coeff. Won't work correctly with coverage stages.\n");
        }
        if (GrBlendCoeffRefsSrc(srcCoeff)) {
            SkDebugf("Unexpected src blend coeff. Won't work correctly with coverage stages.\n");
        }
    #endif
    }

    /**
     * Sets the blending function constant referenced by the following blending
     * coefficients:
     *      kConstC_GrBlendCoeff
     *      kIConstC_GrBlendCoeff
     *      kConstA_GrBlendCoeff
     *      kIConstA_GrBlendCoeff
     *
     * @param constant the constant to set
     */
    void setBlendConstant(GrColor constant) {
        if (constant != fBlendConstant) {
            fBlendConstant = constant;
        }
    }

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name View Matrix
    ////

    /**
     * Retrieves the current view matrix
     * @return the current view matrix.
     */
    const SkMatrix& getViewMatrix() const { return fViewMatrix; }

    /**
     *  Retrieves the inverse of the current view matrix.
     *
     *  If the current view matrix is invertible, return true, and if matrix
     *  is non-null, copy the inverse into it. If the current view matrix is
     *  non-invertible, return false and ignore the matrix parameter.
     *
     * @param matrix if not null, will receive a copy of the current inverse.
     */
    bool getViewInverse(SkMatrix* matrix) const {
        SkMatrix inverse;
        if (fViewMatrix.invert(&inverse)) {
            if (matrix) {
                *matrix = inverse;
            }
            return true;
        }
        return false;
    }

    /**
     * Sets the view matrix to identity and updates any installed effects to compensate for the
     * coord system change.
     */
    bool setIdentityViewMatrix();

    ////////////////////////////////////////////////////////////////////////////

    /**
     * Preconcats the current view matrix and restores the previous view matrix in the destructor.
     * Effect matrices are automatically adjusted to compensate and adjusted back in the destructor.
     */
    class AutoViewMatrixRestore : public ::SkNoncopyable {
    public:
        AutoViewMatrixRestore() : fDrawState(NULL) {}

        AutoViewMatrixRestore(GrDrawState* ds, const SkMatrix& preconcatMatrix) {
            fDrawState = NULL;
            this->set(ds, preconcatMatrix);
        }

        ~AutoViewMatrixRestore() { this->restore(); }

        /**
         * Can be called prior to destructor to restore the original matrix.
         */
        void restore();

        void set(GrDrawState* drawState, const SkMatrix& preconcatMatrix);

        /** Sets the draw state's matrix to identity. This can fail because the current view matrix
            is not invertible. */
        bool setIdentity(GrDrawState* drawState);

    private:
        void doEffectCoordChanges(const SkMatrix& coordChangeMatrix);

        GrDrawState*                                           fDrawState;
        SkMatrix                                               fViewMatrix;
        int                                                    fNumColorStages;
        SkAutoSTArray<8, GrFragmentStage::SavedCoordChange>    fSavedCoordChanges;
    };

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name Render Target
    ////

    /**
     * Retrieves the currently set render-target.
     *
     * @return    The currently set render target.
     */
    GrRenderTarget* getRenderTarget() const { return fRenderTarget.get(); }

    /**
     * Sets the render-target used at the next drawing call
     *
     * @param target  The render target to set.
     */
    void setRenderTarget(GrRenderTarget* target) {
        fRenderTarget.set(SkSafeRef(target), kWrite_GrIOType);
    }

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name Stencil
    ////

    const GrStencilSettings& getStencil() const { return fStencilSettings; }

    /**
     * Sets the stencil settings to use for the next draw.
     * Changing the clip has the side-effect of possibly zeroing
     * out the client settable stencil bits. So multipass algorithms
     * using stencil should not change the clip between passes.
     * @param settings  the stencil settings to use.
     */
    void setStencil(const GrStencilSettings& settings) {
        if (settings != fStencilSettings) {
            fStencilSettings = settings;
        }
    }

    /**
     * Shortcut to disable stencil testing and ops.
     */
    void disableStencil() {
        if (!fStencilSettings.isDisabled()) {
            fStencilSettings.setDisabled();
        }
    }

    GrStencilSettings* stencil() { return &fStencilSettings; }

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name State Flags
    ////

    /**
     *  Flags that affect rendering. Controlled using enable/disableState(). All
     *  default to disabled.
     */
    enum StateBits {
        /**
         * Perform dithering. TODO: Re-evaluate whether we need this bit
         */
        kDither_StateBit        = 0x01,
        /**
         * Perform HW anti-aliasing. This means either HW FSAA, if supported by the render target,
         * or smooth-line rendering if a line primitive is drawn and line smoothing is supported by
         * the 3D API.
         */
        kHWAntialias_StateBit   = 0x02,
        /**
         * Draws will respect the clip, otherwise the clip is ignored.
         */
        kClip_StateBit          = 0x04,
        /**
         * Disables writing to the color buffer. Useful when performing stencil
         * operations.
         */
        kNoColorWrites_StateBit = 0x08,

        /**
         * Usually coverage is applied after color blending. The color is blended using the coeffs
         * specified by setBlendFunc(). The blended color is then combined with dst using coeffs
         * of src_coverage, 1-src_coverage. Sometimes we are explicitly drawing a coverage mask. In
         * this case there is no distinction between coverage and color and the caller needs direct
         * control over the blend coeffs. When set, there will be a single blend step controlled by
         * setBlendFunc() which will use coverage*color as the src color.
         */
         kCoverageDrawing_StateBit = 0x10,
         kLast_StateBit = kCoverageDrawing_StateBit,
    };

    uint32_t getFlagBits() const { return fFlagBits; }

    bool isStateFlagEnabled(uint32_t stateBit) const { return 0 != (stateBit & fFlagBits); }

    bool isClipState() const { return 0 != (fFlagBits & kClip_StateBit); }
    bool isColorWriteDisabled() const { return 0 != (fFlagBits & kNoColorWrites_StateBit); }
    bool isCoverageDrawing() const { return 0 != (fFlagBits & kCoverageDrawing_StateBit); }

    void resetStateFlags() {
        if (0 != fFlagBits) {
            fFlagBits = 0;
        }
    }

    /**
     * Enable render state settings.
     *
     * @param stateBits bitfield of StateBits specifying the states to enable
     */
    void enableState(uint32_t stateBits) {
        if (stateBits & ~fFlagBits) {
            fFlagBits |= stateBits;
        }
    }

    /**
     * Disable render state settings.
     *
     * @param stateBits bitfield of StateBits specifying the states to disable
     */
    void disableState(uint32_t stateBits) {
        if (stateBits & fFlagBits) {
            fFlagBits &= ~(stateBits);
        }
    }

    /**
     * Enable or disable stateBits based on a boolean.
     *
     * @param stateBits bitfield of StateBits to enable or disable
     * @param enable    if true enable stateBits, otherwise disable
     */
    void setState(uint32_t stateBits, bool enable) {
        if (enable) {
            this->enableState(stateBits);
        } else {
            this->disableState(stateBits);
        }
    }

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name Face Culling
    ////

    enum DrawFace {
        kInvalid_DrawFace = -1,

        kBoth_DrawFace,
        kCCW_DrawFace,
        kCW_DrawFace,
    };

    /**
     * Gets whether the target is drawing clockwise, counterclockwise,
     * or both faces.
     * @return the current draw face(s).
     */
    DrawFace getDrawFace() const { return fDrawFace; }

    /**
     * Controls whether clockwise, counterclockwise, or both faces are drawn.
     * @param face  the face(s) to draw.
     */
    void setDrawFace(DrawFace face) {
        SkASSERT(kInvalid_DrawFace != face);
        fDrawFace = face;
    }

    /// @}

    ///////////////////////////////////////////////////////////////////////////
    /// @name Hints
    /// Hints that when provided can enable optimizations.
    ////

    enum Hints {
        kVertexColorsAreOpaque_Hint = 0x1,
        kLast_Hint = kVertexColorsAreOpaque_Hint
    };

    void setHint(Hints hint, bool value) { fHints = value ? (fHints | hint) : (fHints & ~hint); }

    bool vertexColorsAreOpaque() const { return kVertexColorsAreOpaque_Hint & fHints; }

    /// @}

    ///////////////////////////////////////////////////////////////////////////

    /** Return type for CombineIfPossible. */
    enum CombinedState {
        /** The GrDrawStates cannot be combined. */
        kIncompatible_CombinedState,
        /** Either draw state can be used in place of the other. */
        kAOrB_CombinedState,
        /** Use the first draw state. */
        kA_CombinedState,
        /** Use the second draw state. */
        kB_CombinedState,
    };

    /** This function determines whether the GrDrawStates used for two draws can be combined into
        a single GrDrawState. This is used to avoid storing redundant GrDrawStates and to determine
        if draws can be batched. The return value indicates whether combining is possible and, if
        so, which of the two inputs should be used. */
    static CombinedState CombineIfPossible(const GrDrawState& a, const GrDrawState& b,
                                           const GrDrawTargetCaps& caps);

    GrDrawState& operator= (const GrDrawState& that);

private:
    /**
     * Converts refs on GrGpuResources owned directly or indirectly by this GrDrawState into
     * pending reads and writes. This should be called when a GrDrawState is recorded into
     * a GrDrawTarget for later execution. Subclasses of GrDrawState may add setters. However,
     * once this call has been made the GrDrawState is immutable. It is also no longer copyable.
     * In the future this conversion will automatically happen when converting a GrDrawState into
     * an optimized draw state.
     */
    void convertToPendingExec();

    friend class GrDrawTarget;

    bool isEqual(const GrDrawState& that) const;

    /**
     * Optimizations for blending / coverage to that can be applied based on the current state.
     */
    enum BlendOptFlags {
        /**
         * No optimization
         */
        kNone_BlendOpt                  = 0,
        /**
         * Don't draw at all
         */
        kSkipDraw_BlendOptFlag          = 0x1,
        /**
         * The coverage value does not have to be computed separately from alpha, the the output
         * color can be the modulation of the two.
         */
        kCoverageAsAlpha_BlendOptFlag   = 0x2,
        /**
         * Instead of emitting a src color, emit coverage in the alpha channel and r,g,b are
         * "don't cares".
         */
        kEmitCoverage_BlendOptFlag      = 0x4,
        /**
         * Emit transparent black instead of the src color, no need to compute coverage.
         */
        kEmitTransBlack_BlendOptFlag    = 0x8,
    };
    GR_DECL_BITFIELD_OPS_FRIENDS(BlendOptFlags);

    /**
     * Determines what optimizations can be applied based on the blend. The coefficients may have
     * to be tweaked in order for the optimization to work. srcCoeff and dstCoeff are optional
     * params that receive the tweaked coefficients. Normally the function looks at the current
     * state to see if coverage is enabled. By setting forceCoverage the caller can speculatively
     * determine the blend optimizations that would be used if there was partial pixel coverage.
     *
     * Subclasses of GrDrawTarget that actually draw (as opposed to those that just buffer for
     * playback) must call this function and respect the flags that replace the output color.
     *
     * If the cached BlendOptFlags does not have the invalidate bit set, then getBlendOpts will
     * simply returned the cached flags and coefficients. Otherwise it will calculate the values. 
     */
    BlendOptFlags getBlendOpts(bool forceCoverage = false,
                               GrBlendCoeff* srcCoeff = NULL,
                               GrBlendCoeff* dstCoeff = NULL) const;

    const GrProcOptInfo& colorProcInfo() const { 
        this->calcColorInvariantOutput();
        return fColorProcInfo;
    }

    const GrProcOptInfo& coverageProcInfo() const {
        this->calcCoverageInvariantOutput();
        return fCoverageProcInfo;
    }

    /**
     * Determines whether src alpha is guaranteed to be one for all src pixels
     */
    bool srcAlphaWillBeOne() const;

    /**
     * If fColorProcInfoValid is false, function calculates the invariant output for the color
     * stages and results are stored in fColorProcInfo.
     */
    void calcColorInvariantOutput() const;

    /**
     * If fCoverageProcInfoValid is false, function calculates the invariant output for the coverage
     * stages and results are stored in fCoverageProcInfo.
     */
    void calcCoverageInvariantOutput() const;

    void onReset(const SkMatrix* initialViewMatrix);

    // Some of the auto restore objects assume that no effects are removed during their lifetime.
    // This is used to assert that this condition holds.
    SkDEBUGCODE(int fBlockEffectRemovalCnt;)

    void internalSetVertexAttribs(const GrVertexAttrib attribs[], int count, size_t stride);

    typedef GrTGpuResourceRef<GrRenderTarget> ProgramRenderTarget;
    // These fields are roughly sorted by decreasing likelihood of being different in op==
    ProgramRenderTarget                 fRenderTarget;
    GrColor                             fColor;
    SkMatrix                            fViewMatrix;
    GrColor                             fBlendConstant;
    uint32_t                            fFlagBits;
    const GrVertexAttrib*               fVAPtr;
    int                                 fVACount;
    size_t                              fVAStride;
    GrStencilSettings                   fStencilSettings;
    uint8_t                             fCoverage;
    DrawFace                            fDrawFace;
    GrBlendCoeff                        fSrcBlend;
    GrBlendCoeff                        fDstBlend;

    typedef SkSTArray<4, GrFragmentStage> FragmentStageArray;
    typedef GrProgramElementRef<const GrGeometryProcessor> ProgramGeometryProcessor;
    ProgramGeometryProcessor            fGeometryProcessor;
    FragmentStageArray                  fColorStages;
    FragmentStageArray                  fCoverageStages;

    uint32_t                            fHints;

    // This is simply a different representation of info in fVertexAttribs and thus does
    // not need to be compared in op==.
    int fFixedFunctionVertexAttribIndices[kGrFixedFunctionVertexAttribBindingCnt];

    mutable GrProcOptInfo fColorProcInfo;
    mutable GrProcOptInfo fCoverageProcInfo;
    mutable bool fColorProcInfoValid;
    mutable bool fCoverageProcInfoValid;

    friend class GrOptDrawState;
};

GR_MAKE_BITFIELD_OPS(GrDrawState::BlendOptFlags);

#endif