gpu/include/GrDrawTarget.h

/*
    Copyright 2010 Google Inc.

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

         http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
 */


#ifndef GrDrawTarget_DEFINED
#define GrDrawTarget_DEFINED

#include "GrMatrix.h"
#include "GrColor.h"
#include "GrRefCnt.h"
#include "GrSamplerState.h"
#include "GrClip.h"
#include "GrTexture.h"
#include "GrStencil.h"

#include "SkXfermode.h"

class GrTexture;
class GrClipIterator;
class GrVertexBuffer;
class GrIndexBuffer;

class GrDrawTarget : public GrRefCnt {
public:
    /**
     * Number of texture stages. Each stage takes as input a color and
     * 2D texture coordinates. The color input to the first enabled stage is the
     * per-vertex color or the constant color (setColor/setAlpha) if there are
     * no per-vertex colors. For subsequent stages the input color is the output
     * color from the previous enabled stage. The output color of each stage is
     * the input color modulated with the result of a texture lookup. Texture
     * lookups are specified by a texture a sampler (setSamplerState). Texture
     * coordinates for each stage come from the vertices based on a
     * GrVertexLayout bitfield. The output fragment color is the output color of
     * the last enabled stage. The presence or absence of texture coordinates
     * for each stage in the vertex layout indicates whether a stage is enabled
     * or not.
     */
    enum {
        kNumStages = 2,
        kMaxTexCoords = kNumStages
    };

    /**
     *  Bitfield used to indicate which stages are in use.
     */
    typedef int StageBitfield;
    GR_STATIC_ASSERT(sizeof(StageBitfield)*8 >= kNumStages);

    /**
     *  Flags that affect rendering. Controlled using enable/disableState(). All
     *  default to disabled.
     */
    enum StateBits {
        kDither_StateBit        = 0x01, //<! Perform color dithering
        kAntialias_StateBit     = 0x02, //<! Perform anti-aliasing. The render-
                                        //   target must support some form of AA
                                        //   (msaa, coverage sampling, etc). For
                                        //   GrGpu-created rendertarget/textures
                                        //   this is controlled by parameters
                                        //   passed to createTexture.
        kClip_StateBit          = 0x04, //<! Controls whether drawing is clipped
                                        //   against the region specified by
                                        //   setClip.
        kNoColorWrites_StateBit = 0x08, //<! If set it disables writing colors.
                                        //   Useful while performing stencil
                                        //   ops.
        kEdgeAA_StateBit        = 0x10, //<! Perform edge anti-aliasing.
                                        //   Requires the edges to be passed in
                                        //   setEdgeAAData().

        // subclass may use additional bits internally
        kDummyStateBit,
        kLastPublicStateBit = kDummyStateBit-1
    };

    enum DrawFace {
        kBoth_DrawFace,
        kCCW_DrawFace,
        kCW_DrawFace,
    };

    /**
     * The DrawTarget may reserve some of the high bits of the stencil. The draw
     * target will automatically trim reference and mask values so that the
     * client doesn't overwrite these bits.
     * The number of bits available is relative to the currently set render
      *target.
     * @return the number of bits usable by the draw target client.
     */
    int getUsableStencilBits() const {
        int bits = fCurrDrawState.fRenderTarget->stencilBits();
        if (bits) {
            return bits - 1;
        } else {
            return 0;
        }
    }

    /**
     * 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) {
        fCurrDrawState.fStencilSettings = settings;
    }

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

protected:

    struct DrState {
        DrState() {
            // make sure any pad is zero for memcmp
            // all DrState members should default to something
            // valid by the memset
            memset(this, 0, sizeof(DrState));
            
            // memset exceptions
            fColorFilterXfermode = SkXfermode::kDstIn_Mode;
            fFirstCoverageStage = kNumStages;

            // pedantic assertion that our ptrs will
            // be NULL (0 ptr is mem addr 0)
            GrAssert((intptr_t)(void*)NULL == 0LL);

            // default stencil setting should be disabled
            GrAssert(fStencilSettings.isDisabled());
        }
        uint32_t                fFlagBits;
        GrBlendCoeff            fSrcBlend;
        GrBlendCoeff            fDstBlend;
        GrColor                 fBlendConstant;
        GrTexture*              fTextures[kNumStages];
        GrSamplerState          fSamplerStates[kNumStages];
        int                     fFirstCoverageStage;
        GrRenderTarget*         fRenderTarget;
        GrColor                 fColor;
        DrawFace                fDrawFace;
        GrColor                 fColorFilterColor;
        SkXfermode::Mode        fColorFilterXfermode;

        GrStencilSettings       fStencilSettings;
        GrMatrix                fViewMatrix;
        float                   fEdgeAAEdges[18];
        bool operator ==(const DrState& s) const {
            return 0 == memcmp(this, &s, sizeof(DrState));
        }
        bool operator !=(const DrState& s) const { return !(*this == s); }
    };

public:
    ///////////////////////////////////////////////////////////////////////////

    GrDrawTarget();

    /**
     * Sets the current clip to the region specified by clip. All draws will be
     * clipped against this clip if kClip_StateBit is enabled.
     *
     * Setting the clip may (or may not) zero out the client's stencil bits.
     *
     * @param description of the clipping region
     */
    void setClip(const GrClip& clip);

    /**
     * Gets the current clip.
     *
     * @return the clip.
     */
    const GrClip& getClip() const;

    /**
     * Sets the texture used at the next drawing call
     *
     * @param stage The texture stage for which the texture will be set
     *
     * @param texture The texture to set. Can be NULL though there is no advantage
     * to settings a NULL texture if doing non-textured drawing
     */
    void setTexture(int stage, GrTexture* texture);

    /**
     * Retrieves the currently set texture.
     *
     * @return    The currently set texture. The return value will be NULL if no
     *            texture has been set, NULL was most recently passed to
     *            setTexture, or the last setTexture was destroyed.
     */
    const GrTexture* getTexture(int stage) const;
    GrTexture* getTexture(int stage);

    /**
     * Sets the rendertarget used at the next drawing call
     *
     * @param target  The render target to set.
     */
    void setRenderTarget(GrRenderTarget* target);

    /**
     * Retrieves the currently set rendertarget.
     *
     * @return    The currently set render target.
     */
    const GrRenderTarget* getRenderTarget() const;
    GrRenderTarget* getRenderTarget();

    /**
     * Sets the sampler state for a stage used in subsequent draws.
     *
     * The sampler state determines how texture coordinates are
     * intepretted and used to sample the texture.
     *
     * @param stage           the stage of the sampler to set
     * @param samplerState    Specifies the sampler state.
     */
    void setSamplerState(int stage, const GrSamplerState& samplerState);

    /**
     * Concats the matrix of a stage's sampler.
     *
     * @param stage   the stage of the sampler to set
     * @param matrix  the matrix to concat
     */
    void preConcatSamplerMatrix(int stage, const GrMatrix& matrix)  {
        GrAssert(stage >= 0 && stage < kNumStages);
        fCurrDrawState.fSamplerStates[stage].preConcatMatrix(matrix);
    }

    /**
     * Gets the matrix of a stage's sampler
     *
     * @param stage     the stage to of sampler to get
     * @return the sampler state's matrix
     */
    const GrMatrix& getSamplerMatrix(int stage) const {
        return fCurrDrawState.fSamplerStates[stage].getMatrix();
    }

    /**
     * Sets the matrix of a stage's sampler
     *
     * @param stage     the stage of sampler set
     * @param matrix    the matrix to set
     */
    void setSamplerMatrix(int stage, const GrMatrix& matrix) {
        fCurrDrawState.fSamplerStates[stage].setMatrix(matrix);
    }

    /**
     * Sets the matrix applied to veretx positions.
     *
     * In the post-view-matrix space the rectangle [0,w]x[0,h]
     * fully covers the render target. (w and h are the width and height of the
     * the rendertarget.)
     *
     * @param m the matrix used to transform the vertex positions.
     */
    void setViewMatrix(const GrMatrix& m);

    /**
     *  Multiplies the current view matrix by a matrix
     *
     *  After this call V' = V*m where V is the old view matrix,
     *  m is the parameter to this function, and V' is the new view matrix.
     *  (We consider positions to be column vectors so position vector p is
     *  transformed by matrix X as p' = X*p.)
     *
     *  @param m the matrix used to modify the view matrix.
     */
    void preConcatViewMatrix(const GrMatrix& m);

    /**
     *  Multiplies the current view matrix by a matrix
     *
     *  After this call V' = m*V where V is the old view matrix,
     *  m is the parameter to this function, and V' is the new view matrix.
     *  (We consider positions to be column vectors so position vector p is
     *  transformed by matrix X as p' = X*p.)
     *
     *  @param m the matrix used to modify the view matrix.
     */
    void postConcatViewMatrix(const GrMatrix& m);

    /**
     * Retrieves the current view matrix
     * @return the current view matrix.
     */
    const GrMatrix& getViewMatrix() const;

    /**
     *  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(GrMatrix* matrix) const;

    /**
     *  Sets color for next draw to a premultiplied-alpha color.
     *
     *  @param the color to set.
     */
    void setColor(GrColor);

    /**
     * Add a color filter that can be represented by a color and a mode.
     */
    void setColorFilter(GrColor, SkXfermode::Mode);

    /**
     *  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 alpha);

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

    /**
     * A common pattern is to compute a color with the initial stages and then
     * modulate that color by a coverage value in later stage(s) (AA, mask-
     * filters, glyph mask, etc). Color-filters, xfermodes, etc should be 
     * computed based on the pre-coverage-modulated color. The division of 
     * stages between color-computing and coverage-computing is specified by 
     * this method. Initially this is kNumStages (all stages are color-
     * computing).
     */
    void setFirstCoverageStage(int firstCoverageStage) { 
        fCurrDrawState.fFirstCoverageStage = firstCoverageStage; 
    }

    /**
     * Gets the index of the first coverage-computing stage.
     */
    int getFirstCoverageStage() const { 
        return fCurrDrawState.fFirstCoverageStage; 
    }

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

    /**
     * Enable render state settings.
     *
     * @param flags   bitfield of StateBits specifing the states to enable
     */
    void enableState(uint32_t stateBits);

    /**
     * Disable render state settings.
     *
     * @param flags   bitfield of StateBits specifing the states to disable
     */
    void disableState(uint32_t stateBits);

    bool isDitherState() const {
        return 0 != (fCurrDrawState.fFlagBits & kDither_StateBit);
    }

    bool isAntialiasState() const {
        return 0 != (fCurrDrawState.fFlagBits & kAntialias_StateBit);
    }

    bool isClipState() const {
        return 0 != (fCurrDrawState.fFlagBits & kClip_StateBit);
    }

    bool isColorWriteDisabled() const {
        return 0 != (fCurrDrawState.fFlagBits & kNoColorWrites_StateBit);
    }

    /**
     * Sets the blending function coeffecients.
     *
     * 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 coeffecient applied to the src color.
     * @param dstCoef coeffecient applied to the dst color.
     */
    void setBlendFunc(GrBlendCoeff srcCoef, GrBlendCoeff dstCoef);

    /**
     * Sets the blending function constant referenced by the following blending
     * coeffecients:
     *      kConstC_BlendCoeff
     *      kIConstC_BlendCoeff
     *      kConstA_BlendCoeff
     *      kIConstA_BlendCoeff
     *
     * @param constant the constant to set
     */
    void setBlendConstant(GrColor constant) { fCurrDrawState.fBlendConstant = constant; }

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

    /**
     * Used to save and restore the GrGpu's drawing state
     */
    struct SavedDrawState {
    private:
        DrState fState;
        friend class GrDrawTarget;
    };

    /**
     * Saves the current draw state. The state can be restored at a later time
     * with restoreDrawState.
     *
     * See also AutoStateRestore class.
     *
     * @param   state will hold the state after the function returns.
     */
    void saveCurrentDrawState(SavedDrawState* state) const;

    /**
     * Restores previously saved draw state. The client guarantees that state
     * was previously passed to saveCurrentDrawState and that the rendertarget
     * and texture set at save are still valid.
     *
     * See also AutoStateRestore class.
     *
     * @param   state the previously saved state to restore.
     */
    void restoreDrawState(const SavedDrawState& state);

    /**
     * Copies the draw state from another target to this target.
     *
     * @param srcTarget     draw target used as src of the draw state.
     */
    void copyDrawState(const GrDrawTarget& srcTarget);

    /**
     * The format of vertices is represented as a bitfield of flags.
     * Flags that indicate the layout of vertex data. Vertices always contain
     * positions and may also contain up to kMaxTexCoords sets of 2D texture
     * coordinates and per-vertex colors. Each stage can use any of the texture
     * coordinates as its input texture coordinates or it may use the positions.
     *
     * If no texture coordinates are specified for a stage then the stage is
     * disabled.
     *
     * Only one type of texture coord can be specified per stage. For
     * example StageTexCoordVertexLayoutBit(0, 2) and
     * StagePosAsTexCoordVertexLayoutBit(0) cannot both be specified.
     *
     * The order in memory is always (position, texture coord 0, ..., color)
     * with any unused fields omitted. Note that this means that if only texture
     * coordinates 1 is referenced then there is no texture coordinates 0 and
     * the order would be (position, texture coordinate 1[, color]).
     */

    /**
     * Generates a bit indicating that a texture stage uses texture coordinates
     *
     * @param stage       the stage that will use texture coordinates.
     * @param texCoordIdx the index of the texture coordinates to use
     *
     * @return the bit to add to a GrVertexLayout bitfield.
     */
    static int StageTexCoordVertexLayoutBit(int stage, int texCoordIdx) {
        GrAssert(stage < kNumStages);
        GrAssert(texCoordIdx < kMaxTexCoords);
        return 1 << (stage + (texCoordIdx * kNumStages));
    }

    /**
     * Determines if blend is effectively disabled.
     *
     * @return true if blend can be disabled without changing the rendering
     *  result given the current state including the vertex layout specified
     *  with the vertex source.
     */
    bool canDisableBlend() const;

    /**
     * Sets the edge data required for edge antialiasing.
     *
     * @param edges       3 * 6 float values, representing the edge
     *                    equations in Ax + By + C form
     */
     void setEdgeAAData(const float edges[18]);

private:
    static const int TEX_COORD_BIT_CNT = kNumStages*kMaxTexCoords;
public:
    /**
     * Generates a bit indicating that a texture stage uses the position
     * as its texture coordinate.
     *
     * @param stage       the stage that will use position as texture
     *                    coordinates.
     *
     * @return the bit to add to a GrVertexLayout bitfield.
     */
    static int StagePosAsTexCoordVertexLayoutBit(int stage) {
        GrAssert(stage < kNumStages);
        return (1 << (TEX_COORD_BIT_CNT + stage));
    }
private:
    static const int STAGE_BIT_CNT = TEX_COORD_BIT_CNT + kNumStages;

public:

    /**
     * Additional Bits that can be specified in GrVertexLayout.
     */
    enum VertexLayoutBits {

        kColor_VertexLayoutBit              = 1 << (STAGE_BIT_CNT + 0),
                                                //<! vertices have colors
        kTextFormat_VertexLayoutBit         = 1 << (STAGE_BIT_CNT + 1),
                                                //<! use text vertices. (Pos
                                                //   and tex coords may be
                                                //   a different type for
                                                //   text [GrGpuTextVertex vs
                                                //   GrPoint].)
        // for below assert
        kDummyVertexLayoutBit,
        kHighVertexLayoutBit = kDummyVertexLayoutBit - 1
    };
    // make sure we haven't exceeded the number of bits in GrVertexLayout.
    GR_STATIC_ASSERT(kHighVertexLayoutBit < ((uint64_t)1 << 8*sizeof(GrVertexLayout)));

    /**
     * There are three paths for specifying geometry (vertices and optionally
     * indices) to the draw target. When indexed drawing the indices and vertices
     * can be each use a different path.
     *
     * 1. Provide a cpu array (set*SourceToArray). This is useful when the
     *    caller's client has already provided vertex data in a format
     *    the time compatible with a GrVertexLayout. The array must contain the
     *    data at set*SourceToArray is called. The source stays in effect for
     *    drawIndexed & drawNonIndexed calls until set*SourceToArray is called
     *    again or one of the other two paths is chosen.
     *
     * 2. Reserve and Lock. This is most useful when the caller has data it must
     *    transform before drawing and will not likely render it again. The
     *    caller requests that the draw target make room for some amount of
     *    vertex and/or index data. The target provides ptrs to hold the data
     *    data. The caller can write the data into the pts up until the first
     *    drawIndexed or drawNonIndexed call. At this point the data is frozen
     *    and the ptrs are no longer guaranteed to be valid. All subsequent
     *    drawIndexed & drawNonIndexed calls will use this data until
     *    releaseReserved geometry is called. This must be called before another
     *    source is set.
     *
     * 3. Vertex and Index Buffers. This is most useful for geometry that will
     *    be rendered multiple times. SetVertexSourceToBuffer &
     *    SetIndexSourceToBuffer are used to set the buffer and subsequent
     *    drawIndexed and drawNonIndexed calls use this source until another
     *    source is set.
     */

    /**
     * Reserves space for vertices and/or indices. Draw target will use
     * reserved vertices / indices at next draw.
     *
     * If succeeds:
     *          if vertexCount is nonzero, *vertices will be the array
     *          of vertices to be filled by caller. The next draw will read
     *          these vertices.
     *
     *          if indexCount is nonzero, *indices will be the array of indices
     *          to be filled by caller. The next indexed draw will read from
     *          these indices.
     *
     * If a client does not already have a vertex buffer then this is the
     * preferred way to allocate vertex/index array. It allows the subclass of
     * GrDrawTarget to decide whether to put data in buffers, to group vertex
     * data that uses the same state (e.g. for deferred rendering), etc.
     *
     * Following the first draw after reserveAndLockGeometry the ptrs returned
     * by releaseReservedGeometry are no longer valid and the geometry data
     * cannot be further modified. The contents that were put in the reserved
     * space can be drawn by multiple draws, however.
     *
     * reserveAndLockGeometry must be matched with a releaseReservedGeometry
     * call after all draws that reference the reserved geometry data have
     * been called.
     *
     * AutoGeometryRelease can be used to automatically call the release.
     *
     * @param vertexCount  the number of vertices to reserve space for. Can be 0.
     * @param indexCount   the number of indices to reserve space for. Can be 0.
     * @param vertexLayout the format of vertices (ignored if vertexCount == 0).
     * @param vertices     will point to reserved vertex space if vertexCount is
     *                     non-zero. Illegal to pass NULL if vertexCount > 0.
     * @param indices      will point to reserved index space if indexCount is
     *                     non-zero. Illegal to pass NULL if indexCount > 0.
     *
     * @return  true if succeeded in allocating space for the vertices and false
     *               if not.
     */
    bool reserveAndLockGeometry(GrVertexLayout    vertexLayout,
                                uint32_t          vertexCount,
                                uint32_t          indexCount,
                                void**            vertices,
                                void**            indices);
    /**
     * Provides hints to caller about the number of vertices and indices
     * that can be allocated cheaply. This can be useful if caller is reserving
     * space but doesn't know exactly how much geometry is needed.
     *
     * Also may hint whether the draw target should be flushed first. This is
     * useful for deferred targets.
     *
     * @param vertexLayout layout of vertices caller would like to reserve
     * @param vertexCount  in: hint about how many vertices the caller would
     *                     like to allocate.
     *                     out: a hint about the number of vertices that can be
     *                     allocated cheaply. Negative means no hint.
     *                     Ignored if NULL.
     * @param indexCount   in: hint about how many indices the caller would
     *                     like to allocate.
     *                     out: a hint about the number of indices that can be
     *                     allocated cheaply. Negative means no hint.
     *                     Ignored if NULL.
     *
     * @return  true if target should be flushed based on the input values.
     */
    virtual bool geometryHints(GrVertexLayout vertexLayout,
                               int* vertexCount,
                               int* indexCount) const;

    /**
     * Releases reserved vertex/index data from reserveAndLockGeometry().
     */
    void releaseReservedGeometry();

    /**
     * Sets source of vertex data for the next draw. Array must contain
     * the vertex data when this is called.
     *
     * @param array         cpu array containing vertex data.
     * @param size          size of the vertex data.
     * @param vertexCount   the number of vertices in the array.
     */
    void setVertexSourceToArray(GrVertexLayout vertexLayout,
                                const void* vertexArray,
                                int vertexCount);

    /**
     * Sets source of index data for the next indexed draw. Array must contain
     * the indices when this is called.
     *
     * @param array         cpu array containing index data.
     * @param indexCount    the number of indices in the array.
     */
    void setIndexSourceToArray(const void* indexArray, int indexCount);

    /**
     * Sets source of vertex data for the next draw. Data does not have to be
     * in the buffer until drawIndexed or drawNonIndexed.
     *
     * @param buffer        vertex buffer containing vertex data. Must be
     *                      unlocked before draw call.
     * @param vertexLayout  layout of the vertex data in the buffer.
     */
    void setVertexSourceToBuffer(GrVertexLayout vertexLayout,
                                 const GrVertexBuffer* buffer);

    /**
     * Sets source of index data for the next indexed draw. Data does not have
     * to be in the buffer until drawIndexed or drawNonIndexed.
     *
     * @param buffer index buffer containing indices. Must be unlocked
     *               before indexed draw call.
     */
    void setIndexSourceToBuffer(const GrIndexBuffer* buffer);

    /**
     * Draws indexed geometry using the current state and current vertex / index
     * sources.
     *
     * @param type         The type of primitives to draw.
     * @param startVertex  the vertex in the vertex array/buffer corresponding
     *                     to index 0
     * @param startIndex   first index to read from index src.
     * @param vertexCount  one greater than the max index.
     * @param indexCount   the number of index elements to read. The index count
     *                     is effectively trimmed to the last completely
     *                     specified primitive.
     */
    virtual void drawIndexed(GrPrimitiveType type,
                             int startVertex,
                             int startIndex,
                             int vertexCount,
                             int indexCount) = 0;

    /**
     * Draws non-indexed geometry using the current state and current vertex
     * sources.
     *
     * @param type         The type of primitives to draw.
     * @param startVertex  the vertex in the vertex array/buffer corresponding
     *                     to index 0
     * @param vertexCount  one greater than the max index.
     */
    virtual void drawNonIndexed(GrPrimitiveType type,
                                int startVertex,
                                int vertexCount)  = 0;

    /**
     * Helper function for drawing rects. This does not use the current index
     * and vertex sources. After returning, the vertex and index sources may
     * have changed. They should be reestablished before the next drawIndexed
     * or drawNonIndexed. This cannot be called between reserving and releasing
     * geometry. The GrDrawTarget subclass may be able to perform additional
     * optimizations if drawRect is used rather than drawIndexed or
     * drawNonIndexed.
     * @param rect      the rect to draw
     * @param matrix    optional matrix applied to rect (before viewMatrix)
     * @param stageEnableBitfield bitmask indicating which stages are enabled.
     *                            Bit i indicates whether stage i is enabled.
     * @param srcRects  specifies rects for stages enabled by stageEnableMask.
     *                  if stageEnableMask bit i is 1, srcRects is not NULL,
     *                  and srcRects[i] is not NULL, then srcRects[i] will be
     *                  used as coordinates for stage i. Otherwise, if stage i
     *                  is enabled then rect is used as the coordinates.
     * @param srcMatrices   optional matrices applied to srcRects. If
     *                      srcRect[i] is non-NULL and srcMatrices[i] is
     *                      non-NULL then srcRect[i] will be transformed by
     *                      srcMatrix[i]. srcMatrices can be NULL when no
     *                      srcMatrices are desired.
     */
    virtual void drawRect(const GrRect& rect,
                          const GrMatrix* matrix,
                          StageBitfield stageEnableBitfield,
                          const GrRect* srcRects[],
                          const GrMatrix* srcMatrices[]);

    /**
     * Helper for drawRect when the caller doesn't need separate src rects or
     * matrices.
     */
    void drawSimpleRect(const GrRect& rect,
                        const GrMatrix* matrix,
                        StageBitfield stageEnableBitfield) {
         drawRect(rect, matrix, stageEnableBitfield, NULL, NULL);
    }

    /**
     * Clear the render target. Ignores the clip and all other draw state
     * (blend mode, stages, etc). Clears the whole thing if rect is NULL,
     * otherwise just the rect.
     */
    virtual void clear(const GrIRect* rect, GrColor color) = 0;

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

    class AutoStateRestore : ::GrNoncopyable {
    public:
        AutoStateRestore();
        AutoStateRestore(GrDrawTarget* target);
        ~AutoStateRestore();

        /**
         * if this object is already saving state for param target then
         * this does nothing. Otherise, it restores previously saved state on
         * previous target (if any) and saves current state on param target.
         */
        void set(GrDrawTarget* target);

    private:
        GrDrawTarget*       fDrawTarget;
        SavedDrawState      fDrawState;
    };

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

    class AutoViewMatrixRestore : ::GrNoncopyable {
    public:
        AutoViewMatrixRestore() {
            fDrawTarget = NULL;
        }

        AutoViewMatrixRestore(GrDrawTarget* target)
            : fDrawTarget(target), fMatrix(fDrawTarget->getViewMatrix()) {
            GrAssert(NULL != target);
        }

        void set(GrDrawTarget* target) {
            GrAssert(NULL != target);
            if (NULL != fDrawTarget) {
                fDrawTarget->setViewMatrix(fMatrix);
            }
            fDrawTarget = target;
            fMatrix = target->getViewMatrix();
        }

        ~AutoViewMatrixRestore() {
            if (NULL != fDrawTarget) {
                fDrawTarget->setViewMatrix(fMatrix);
            }
        }

    private:
        GrDrawTarget*       fDrawTarget;
        GrMatrix            fMatrix;
    };

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

    class AutoReleaseGeometry : ::GrNoncopyable {
    public:
        AutoReleaseGeometry(GrDrawTarget*  target,
                            GrVertexLayout vertexLayout,
                            uint32_t       vertexCount,
                            uint32_t       indexCount) {
            fTarget = NULL;
            this->set(target, vertexLayout, vertexCount, indexCount);
        }

        AutoReleaseGeometry() {
            fTarget = NULL;
        }

        ~AutoReleaseGeometry() {
            if (NULL != fTarget) {
                fTarget->releaseReservedGeometry();
            }
        }

        bool set(GrDrawTarget*  target,
                 GrVertexLayout vertexLayout,
                 uint32_t       vertexCount,
                 uint32_t       indexCount) {
            if (NULL != fTarget) {
                fTarget->releaseReservedGeometry();
            }
            fTarget = target;
            if (NULL != fTarget) {
                if (!fTarget->reserveAndLockGeometry(vertexLayout,
                                                     vertexCount,
                                                     indexCount,
                                                     &fVertices,
                                                     &fIndices)) {
                    fTarget = NULL;
                }
            }
            return NULL != fTarget;
        }

        bool succeeded() const { return NULL != fTarget; }
        void* vertices() const { return fVertices; }
        void* indices() const { return fIndices; }

        GrPoint* positions() const {
            return static_cast<GrPoint*>(fVertices);
        }

    private:
        GrDrawTarget* fTarget;
        void*         fVertices;
        void*         fIndices;
    };

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

    class AutoClipRestore : ::GrNoncopyable {
    public:
        AutoClipRestore(GrDrawTarget* target) {
            fTarget = target;
            fClip = fTarget->getClip();
        }

        ~AutoClipRestore() {
            fTarget->setClip(fClip);
        }
    private:
        GrDrawTarget* fTarget;
        GrClip        fClip;
    };

    ////////////////////////////////////////////////////////////////////////////
    // Helpers for picking apart vertex layouts

    /**
     * Helper function to compute the size of a vertex from a vertex layout
     * @return size of a single vertex.
     */
    static size_t VertexSize(GrVertexLayout vertexLayout);

    /**
     * Helper function for determining the index of texture coordinates that
     * is input for a texture stage. Note that a stage may instead use positions
     * as texture coordinates, in which case the result of the function is
     * indistinguishable from the case when the stage is disabled.
     *
     * @param stage         the stage to query
     * @param vertexLayout  layout to query
     *
     * @return the texture coordinate index or -1 if the stage doesn't use
     *         separate (non-position) texture coordinates.
     */
    static int VertexTexCoordsForStage(int stage, GrVertexLayout vertexLayout);

    /**
     * Helper function to compute the offset of texture coordinates in a vertex
     * @return offset of texture coordinates in vertex layout or -1 if the
     *         layout has no texture coordinates. Will be 0 if positions are
     *         used as texture coordinates for the stage.
     */
    static int VertexStageCoordOffset(int stage, GrVertexLayout vertexLayout);

    /**
     * Helper function to compute the offset of the color in a vertex
     * @return offset of color in vertex layout or -1 if the
     *         layout has no color.
     */
    static int VertexColorOffset(GrVertexLayout vertexLayout);

    /**
     * Helper function to determine if vertex layout contains explicit texture
     * coordinates of some index.
     *
     * @param coordIndex    the tex coord index to query
     * @param vertexLayout  layout to query
     *
     * @return true if vertex specifies texture coordinates for the index,
     *              false otherwise.
     */
    static bool VertexUsesTexCoordIdx(int coordIndex,
                                      GrVertexLayout vertexLayout);

    /**
     * Helper function to determine if vertex layout contains either explicit or
     * implicit texture coordinates for a stage.
     *
     * @param stage         the stage to query
     * @param vertexLayout  layout to query
     *
     * @return true if vertex specifies texture coordinates for the stage,
     *              false otherwise.
     */
    static bool VertexUsesStage(int stage, GrVertexLayout vertexLayout);

    /**
     * Helper function to compute the size of each vertex and the offsets of
     * texture coordinates and color. Determines tex coord offsets by tex coord
     * index rather than by stage. (Each stage can be mapped to any t.c. index
     * by StageTexCoordVertexLayoutBit.)
     *
     * @param vertexLayout          the layout to query
     * @param texCoordOffsetsByIdx  after return it is the offset of each
     *                              tex coord index in the vertex or -1 if
     *                              index isn't used.
     * @return size of a single vertex
     */
    static int VertexSizeAndOffsetsByIdx(GrVertexLayout vertexLayout,
                                         int texCoordOffsetsByIdx[kMaxTexCoords],
                                         int *colorOffset);

    /**
     * Helper function to compute the size of each vertex and the offsets of
     * texture coordinates and color. Determines tex coord offsets by stage
     * rather than by index. (Each stage can be mapped to any t.c. index
     * by StageTexCoordVertexLayoutBit.) If a stage uses positions for
     * tex coords then that stage's offset will be 0 (positions are always at 0).
     *
     * @param vertexLayout              the layout to query
     * @param texCoordOffsetsByStage    after return it is the offset of each
     *                                  tex coord index in the vertex or -1 if
     *                                  index isn't used.
     * @return size of a single vertex
     */
    static int VertexSizeAndOffsetsByStage(GrVertexLayout vertexLayout,
                                           int texCoordOffsetsByStage[kNumStages],
                                           int *colorOffset);

    /**
     * Accessing positions, texture coords, or colors, of a vertex within an
     * array is a hassle involving casts and simple math. These helpers exist
     * to keep GrDrawTarget clients' code a bit nicer looking.
     */

    /**
     * Gets a pointer to a GrPoint of a vertex's position or texture
     * coordinate.
     * @param vertices      the vetex array
     * @param vertexIndex   the index of the vertex in the array
     * @param vertexSize    the size of each vertex in the array
     * @param offset        the offset in bytes of the vertex component.
     *                      Defaults to zero (corresponding to vertex position)
     * @return pointer to the vertex component as a GrPoint
     */
    static GrPoint* GetVertexPoint(void* vertices,
                                   int vertexIndex,
                                   int vertexSize,
                                   int offset = 0) {
        intptr_t start = GrTCast<intptr_t>(vertices);
        return GrTCast<GrPoint*>(start + offset +
                                 vertexIndex * vertexSize);
    }
    static const GrPoint* GetVertexPoint(const void* vertices,
                                         int vertexIndex,
                                         int vertexSize,
                                         int offset = 0) {
        intptr_t start = GrTCast<intptr_t>(vertices);
        return GrTCast<const GrPoint*>(start + offset +
                                       vertexIndex * vertexSize);
    }

    /**
     * Gets a pointer to a GrColor inside a vertex within a vertex array.
     * @param vertices      the vetex array
     * @param vertexIndex   the index of the vertex in the array
     * @param vertexSize    the size of each vertex in the array
     * @param offset        the offset in bytes of the vertex color
     * @return pointer to the vertex component as a GrColor
     */
    static GrColor* GetVertexColor(void* vertices,
                                   int vertexIndex,
                                   int vertexSize,
                                   int offset) {
        intptr_t start = GrTCast<intptr_t>(vertices);
        return GrTCast<GrColor*>(start + offset +
                                 vertexIndex * vertexSize);
    }
    static const GrColor* GetVertexColor(const void* vertices,
                                         int vertexIndex,
                                         int vertexSize,
                                         int offset) {
        const intptr_t start = GrTCast<intptr_t>(vertices);
        return GrTCast<const GrColor*>(start + offset +
                                       vertexIndex * vertexSize);
    }

    static void VertexLayoutUnitTest();

protected:
    // given a vertex layout and a draw state, will a stage be used?
    static bool StageWillBeUsed(int stage, GrVertexLayout layout, 
                         const DrState& state) {
        return NULL != state.fTextures[stage] && VertexUsesStage(stage, layout);
    }

    bool isStageEnabled(int stage) const {
        return StageWillBeUsed(stage, fGeometrySrc.fVertexLayout, fCurrDrawState);
    }

    // Helpers for GrDrawTarget subclasses that won't have private access to
    // SavedDrawState but need to peek at the state values.
    static DrState& accessSavedDrawState(SavedDrawState& sds)
                                                        { return sds.fState; }
    static const DrState& accessSavedDrawState(const SavedDrawState& sds)
                                                        { return sds.fState; }

    // implemented by subclass
    virtual bool onAcquireGeometry(GrVertexLayout vertexLayout,
                                   void** vertices,
                                   void** indices) = 0;

    virtual void onReleaseGeometry() = 0;

    // subclass overrides to be notified when clip is set.
    virtual void clipWillBeSet(const GrClip& clip) = 0;

    virtual void onSetVertexSourceToArray(const void* vertexArray,
                                          int vertexCount) = 0;

    virtual void onSetIndexSourceToArray(const void* indexArray,
                                         int indexCount) = 0;

    // Helpers for drawRect, protected so subclasses that override drawRect
    // can use them.
    static GrVertexLayout GetRectVertexLayout(StageBitfield stageEnableBitfield,
                                              const GrRect* srcRects[]);

    static void SetRectVertices(const GrRect& rect,
                                const GrMatrix* matrix,
                                const GrRect* srcRects[],
                                const GrMatrix* srcMatrices[],
                                GrVertexLayout layout,
                                void* vertices);

    enum GeometrySrcType {
        kReserved_GeometrySrcType,  // src was set using reserveAndLockGeometry
        kArray_GeometrySrcType,     // src was set using set*SourceToArray
        kBuffer_GeometrySrcType     // src was set using set*SourceToBuffer
    };

    struct ReservedGeometry {
        bool            fLocked;
        uint32_t        fVertexCount;
        uint32_t        fIndexCount;
    } fReservedGeometry;

    struct GeometrySrc {
        GeometrySrcType         fVertexSrc;
        const GrVertexBuffer*   fVertexBuffer; // valid if src type is buffer
        GeometrySrcType         fIndexSrc;
        const GrIndexBuffer*    fIndexBuffer; // valid if src type is buffer
        GrVertexLayout          fVertexLayout;
    } fGeometrySrc;

    GrClip fClip;

    DrState fCurrDrawState;

    // Not meant for external use. Only setVertexSourceToBuffer and
    // setIndexSourceToBuffer will work since GrDrawTarget subclasses don't
    // support nested reserveAndLockGeometry (and cpu arrays internally use the
    // same path).
    class AutoGeometrySrcRestore {
    public:
        AutoGeometrySrcRestore(GrDrawTarget* target) {
            fTarget = target;
            fGeometrySrc = fTarget->fGeometrySrc;
        }
        ~AutoGeometrySrcRestore() {
            fTarget->fGeometrySrc = fGeometrySrc;
        }
    private:
        GrDrawTarget *fTarget;
        GeometrySrc  fGeometrySrc;

        AutoGeometrySrcRestore();
        AutoGeometrySrcRestore(const AutoGeometrySrcRestore&);
        AutoGeometrySrcRestore& operator =(AutoGeometrySrcRestore&);
    };
};

#endif