skia2/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 "GrSurface.h"
#include "SkRect.h"

class GrStencilBuffer;
class GrRenderTargetPriv;

/**
 * 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_SurfaceFlag flag.
 * Additionally, GrContext provides methods for creating GrRenderTargets
 * that wrap externally created render targets.
 */
class GrRenderTarget : virtual public GrSurface {
public:
    SK_DECLARE_INST_COUNT(GrRenderTarget)

    // GrSurface overrides
    GrRenderTarget* asRenderTarget() SK_OVERRIDE { return this; }
    const GrRenderTarget* asRenderTarget() const  SK_OVERRIDE { return this; }

    // GrRenderTarget
    /**
     * @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 SkIRect* rect = NULL);

    /**
     * Call to override the region that needs to be resolved.
     */
    void overrideResolveRect(const SkIRect 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 SkIRect& getResolveRect() const { return fResolveRect; }

    /**
     * Provide a performance hint that the render target's contents are allowed
     * to become undefined.
     */
    void discard();

    // 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;

    // Provides access to functions that aren't part of the public API.
    GrRenderTargetPriv renderTargetPriv();
    const GrRenderTargetPriv renderTargetPriv() const;

protected:
    GrRenderTarget(GrGpu* gpu, LifeCycle lifeCycle, const GrSurfaceDesc& desc)
        : INHERITED(gpu, lifeCycle, desc)
        , fStencilBuffer(NULL) {
        fResolveRect.setLargestInverted();
    }

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

private:
    // Checked when this object is asked to attach a stencil buffer.
    virtual bool canAttemptStencilAttachment() const = 0;

    friend class GrRenderTargetPriv;

    GrStencilBuffer*  fStencilBuffer;

    SkIRect           fResolveRect;

    typedef GrSurface INHERITED;
};

#endif