void
GLScreenBuffer::Attach(SharedSurface* surface, const gfx::IntSize& size)
{
    ScopedBindFramebuffer autoFB(mGL);

    SharedSurface_GL* surf = SharedSurface_GL::Cast(surface);
    if (mRead && SharedSurf())
        SharedSurf()->UnlockProd();

    surf->LockProd();

    if (mRead &&
        surf->AttachType() == SharedSurf()->AttachType() &&
        size == Size())
    {
        // Same size, same type, ready for reuse!
        mRead->Attach(surf);
    } else {
        // Else something changed, so resize:
        DrawBuffer* draw = CreateDraw(size);  // Can be null.
        ReadBuffer* read = CreateRead(surf);
        MOZ_ASSERT(read); // Should never fail if SwapProd succeeded.

        delete mDraw;
        delete mRead;

        mDraw = draw;
        mRead = read;
    }

    // Check that we're all set up.
    MOZ_ASSERT(SharedSurf() == surf);

    if (!PreserveBuffer()) {
        // DiscardFramebuffer here could help perf on some mobile platforms.
    }
}
// |src| must begin and end locked, though we may
// temporarily unlock it if we need to.
void
SharedSurface_GL::ProdCopy(SharedSurface_GL* src, SharedSurface_GL* dest,
                           SurfaceFactory_GL* factory)
{
    GLContext* gl = src->GL();

    gl->MakeCurrent();

    if (src->AttachType() == AttachmentType::Screen &&
        dest->AttachType() == AttachmentType::Screen)
    {
        // Here, we actually need to blit through a temp surface, so let's make one.
        nsAutoPtr<SharedSurface_GLTexture> tempSurf(
            SharedSurface_GLTexture::Create(gl, gl,
                                            factory->Formats(),
                                            src->Size(),
                                            factory->Caps().alpha));

        ProdCopy(src, tempSurf, factory);
        ProdCopy(tempSurf, dest, factory);
        return;
    }

    if (src->AttachType() == AttachmentType::Screen) {
        SharedSurface_GL* origLocked = gl->GetLockedSurface();
        bool srcNeedsUnlock = false;
        bool origNeedsRelock = false;
        if (origLocked != src) {
            if (origLocked) {
                origLocked->UnlockProd();
                origNeedsRelock = true;
            }

            src->LockProd();
            srcNeedsUnlock = true;
        }

        if (dest->AttachType() == AttachmentType::GLTexture) {
            GLuint destTex = dest->ProdTexture();
            GLenum destTarget = dest->ProdTextureTarget();

            gl->BlitHelper()->BlitFramebufferToTexture(0, destTex, src->Size(), dest->Size(), destTarget);
        } else if (dest->AttachType() == AttachmentType::GLRenderbuffer) {
            GLuint destRB = dest->ProdRenderbuffer();
            ScopedFramebufferForRenderbuffer destWrapper(gl, destRB);

            gl->BlitHelper()->BlitFramebufferToFramebuffer(0, destWrapper.FB(),
                                                           src->Size(), dest->Size());
        } else {
            MOZ_CRASH("Unhandled dest->AttachType().");
        }

        if (srcNeedsUnlock)
            src->UnlockProd();

        if (origNeedsRelock)
            origLocked->LockProd();

        return;
    }

    if (dest->AttachType() == AttachmentType::Screen) {
        SharedSurface_GL* origLocked = gl->GetLockedSurface();
        bool destNeedsUnlock = false;
        bool origNeedsRelock = false;
        if (origLocked != dest) {
            if (origLocked) {
                origLocked->UnlockProd();
                origNeedsRelock = true;
            }

            dest->LockProd();
            destNeedsUnlock = true;
        }

        if (src->AttachType() == AttachmentType::GLTexture) {
            GLuint srcTex = src->ProdTexture();
            GLenum srcTarget = src->ProdTextureTarget();

            gl->BlitHelper()->BlitTextureToFramebuffer(srcTex, 0, src->Size(), dest->Size(), srcTarget);
        } else if (src->AttachType() == AttachmentType::GLRenderbuffer) {
            GLuint srcRB = src->ProdRenderbuffer();
            ScopedFramebufferForRenderbuffer srcWrapper(gl, srcRB);

            gl->BlitHelper()->BlitFramebufferToFramebuffer(srcWrapper.FB(), 0,
                                                           src->Size(), dest->Size());
        } else {
            MOZ_CRASH("Unhandled src->AttachType().");
        }

        if (destNeedsUnlock)
            dest->UnlockProd();

        if (origNeedsRelock)
            origLocked->LockProd();

        return;
    }

    // Alright, done with cases involving Screen types.
    // Only {src,dest}x{texture,renderbuffer} left.

    if (src->AttachType() == AttachmentType::GLTexture) {
        GLuint srcTex = src->ProdTexture();
        GLenum srcTarget = src->ProdTextureTarget();

        if (dest->AttachType() == AttachmentType::GLTexture) {
            GLuint destTex = dest->ProdTexture();
            GLenum destTarget = dest->ProdTextureTarget();

            gl->BlitHelper()->BlitTextureToTexture(srcTex, destTex,
                                                   src->Size(), dest->Size(),
                                                   srcTarget, destTarget);

            return;
        }

        if (dest->AttachType() == AttachmentType::GLRenderbuffer) {
            GLuint destRB = dest->ProdRenderbuffer();
            ScopedFramebufferForRenderbuffer destWrapper(gl, destRB);

            gl->BlitHelper()->BlitTextureToFramebuffer(srcTex, destWrapper.FB(),
                                                       src->Size(), dest->Size(), srcTarget);

            return;
        }

        MOZ_CRASH("Unhandled dest->AttachType().");
    }

    if (src->AttachType() == AttachmentType::GLRenderbuffer) {
        GLuint srcRB = src->ProdRenderbuffer();
        ScopedFramebufferForRenderbuffer srcWrapper(gl, srcRB);

        if (dest->AttachType() == AttachmentType::GLTexture) {
            GLuint destTex = dest->ProdTexture();
            GLenum destTarget = dest->ProdTextureTarget();

            gl->BlitHelper()->BlitFramebufferToTexture(srcWrapper.FB(), destTex,
                                                       src->Size(), dest->Size(), destTarget);

            return;
        }

        if (dest->AttachType() == AttachmentType::GLRenderbuffer) {
            GLuint destRB = dest->ProdRenderbuffer();
            ScopedFramebufferForRenderbuffer destWrapper(gl, destRB);

            gl->BlitHelper()->BlitFramebufferToFramebuffer(srcWrapper.FB(), destWrapper.FB(),
                                                           src->Size(), dest->Size());

            return;
        }

        MOZ_CRASH("Unhandled dest->AttachType().");
    }

    MOZ_CRASH("Unhandled src->AttachType().");
}