include/gpu/GrRenderTarget.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 GrRenderTarget_DEFINED
#define GrRenderTarget_DEFINED

#include "GrRect.h"
#include "GrSurface.h"

class GrStencilBuffer;
class GrTexture;

/**
 * GrRenderTarget represents a 2D buffer of pixels that can be rendered to.
 * A context's render target is set by setRenderTarget(). Render targets are
 * created by a createTexture with the kRenderTarget_TextureFlag flag.
 * Additionally, GrContext provides methods for creating GrRenderTargets
 * that wrap externally created render targets.
 */
class GrRenderTarget : public GrSurface {
public:
    SK_DECLARE_INST_COUNT(GrRenderTarget)

    // GrResource overrides
    virtual size_t sizeInBytes() const SK_OVERRIDE;

    // GrSurface overrides
    /**
     * @return the texture associated with the render target, may be NULL.
     */
    virtual GrTexture* asTexture() SK_OVERRIDE { return fTexture; }
    virtual const GrTexture* asTexture() const SK_OVERRIDE { return fTexture; }

    /**
     * @return this render target.
     */
    virtual GrRenderTarget* asRenderTarget() SK_OVERRIDE { return this; }
    virtual const GrRenderTarget* asRenderTarget() const  SK_OVERRIDE {
        return this;
    }

    virtual bool readPixels(int left, int top, int width, int height,
                            GrPixelConfig config,
                            void* buffer,
                            size_t rowBytes = 0,
                            uint32_t pixelOpsFlags = 0) SK_OVERRIDE;

    virtual void writePixels(int left, int top, int width, int height,
                             GrPixelConfig config,
                             const void* buffer,
                             size_t rowBytes = 0,
                             uint32_t pixelOpsFlags = 0) SK_OVERRIDE;

    // GrRenderTarget
    /**
     * If this RT is multisampled, this is the multisample buffer
     * @return the 3D API's handle to this object (e.g. FBO ID in OpenGL)
     */
    virtual GrBackendObject getRenderTargetHandle() const = 0;

    /**
     * If this RT is multisampled, this is the buffer it is resolved to.
     * Otherwise, same as getRenderTargetHandle().
     * (In GL a separate FBO ID is used for the MSAA and resolved buffers)
     * @return the 3D API's handle to this object (e.g. FBO ID in OpenGL)
     */
    virtual GrBackendObject getRenderTargetResolvedHandle() const = 0;

    /**
     * @return true if the surface is multisampled, false otherwise
     */
    bool isMultisampled() const { return 0 != fDesc.fSampleCnt; }

    /**
     * @return the number of samples-per-pixel or zero if non-MSAA.
     */
    int numSamples() const { return fDesc.fSampleCnt; }

    /**
     * Call to indicate the multisample contents were modified such that the
     * render target needs to be resolved before it can be used as texture. Gr
     * tracks this for its own drawing and thus this only needs to be called
     * when the render target has been modified outside of Gr. This has no
     * effect on wrapped backend render targets.
     *
     * @param rect  a rect bounding the area needing resolve. NULL indicates
     *              the whole RT needs resolving.
     */
    void flagAsNeedingResolve(const GrIRect* rect = NULL);

    /**
     * Call to override the region that needs to be resolved.
     */
    void overrideResolveRect(const GrIRect rect);

    /**
     * Call to indicate that GrRenderTarget was externally resolved. This may
     * allow Gr to skip a redundant resolve step.
     */
    void flagAsResolved() { fResolveRect.setLargestInverted(); }

    /**
     * @return true if the GrRenderTarget requires MSAA resolving
     */
    bool needsResolve() const { return !fResolveRect.isEmpty(); }

    /**
     * Returns a rect bounding the region needing resolving.
     */
    const GrIRect& getResolveRect() const { return fResolveRect; }

    /**
     * If the render target is multisampled this will perform a multisample
     * resolve. Any pending draws to the target are first flushed. This only
     * applies to render targets that are associated with GrTextures. After the
     * function returns the GrTexture will contain the resolved pixels.
     */
    void resolve();

    // a MSAA RT may require explicit resolving , it may auto-resolve (e.g. FBO
    // 0 in GL), or be unresolvable because the client didn't give us the
    // resolve destination.
    enum ResolveType {
        kCanResolve_ResolveType,
        kAutoResolves_ResolveType,
        kCantResolve_ResolveType,
    };
    virtual ResolveType getResolveType() const = 0;

    /**
     * GrStencilBuffer is not part of the public API.
     */
    GrStencilBuffer* getStencilBuffer() const { return fStencilBuffer; }
    void setStencilBuffer(GrStencilBuffer* stencilBuffer);

protected:
    GrRenderTarget(GrGpu* gpu,
                   bool isWrapped,
                   GrTexture* texture,
                   const GrTextureDesc& desc,
                   GrSurfaceOrigin origin)
        : INHERITED(gpu, isWrapped, desc, origin)
        , fStencilBuffer(NULL)
        , fTexture(texture) {
        fResolveRect.setLargestInverted();
    }

    friend class GrTexture;
    // When a texture unrefs an owned render target this func
    // removes the back pointer. This could be called from
    // texture's destructor but would have to be done in derived
    // classes. By the time of texture base destructor it has already
    // lost its pointer to the rt.
    void onTextureReleaseRenderTarget() {
        GrAssert(NULL != fTexture);
        fTexture = NULL;
    }

    // override of GrResource
    virtual void onAbandon() SK_OVERRIDE;
    virtual void onRelease() SK_OVERRIDE;

private:
    GrStencilBuffer*  fStencilBuffer;
    GrTexture*        fTexture; // not ref'ed

    GrIRect           fResolveRect;

    typedef GrSurface INHERITED;
};

#endif