Add discard API to SkCanvas, plumb it to glDiscardFramebuffer()

BUG=skia:2349
R=robertphillips@google.com, reed@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/211683002

git-svn-id: http://skia.googlecode.com/svn/trunk@13976 2bbb7eff-a529-9590-31e7-b0007b416f81

5 files changed, 27 insertions, 8 deletions

diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 47f3f0f0c8..bf7939ccee 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -45,7 +45,6 @@ void GrGLCaps::reset() {
     fUseNonVBOVertexAndIndexDynamicData = false;
     fIsCoreProfile = false;
     fFixedFunctionSupport = false;
-    fDiscardFBSupport = false;
     fFullClearIsFree = false;
     fDropsTileOnZeroDivide = false;
 }
@@ -83,7 +82,6 @@ GrGLCaps& GrGLCaps::operator = (const GrGLCaps& caps) {
     fUseNonVBOVertexAndIndexDynamicData = caps.fUseNonVBOVertexAndIndexDynamicData;
     fIsCoreProfile = caps.fIsCoreProfile;
     fFixedFunctionSupport = caps.fFixedFunctionSupport;
-    fDiscardFBSupport = caps.fDiscardFBSupport;
     fFullClearIsFree = caps.fFullClearIsFree;
     fDropsTileOnZeroDivide = caps.fDropsTileOnZeroDivide;
 
@@ -224,7 +222,7 @@ void GrGLCaps::init(const GrGLContextInfo& ctxInfo, const GrGLInterface* gli) {
         fUseNonVBOVertexAndIndexDynamicData = true;
     }
 
-    fDiscardFBSupport = ctxInfo.hasExtension("GL_EXT_discard_framebuffer");
+    fDiscardRenderTargetSupport = ctxInfo.hasExtension("GL_EXT_discard_framebuffer");
 
     if (kARM_GrGLVendor == ctxInfo.vendor() || kImagination_GrGLVendor == ctxInfo.vendor()) {
         fFullClearIsFree = true;
@@ -664,7 +662,6 @@ SkString GrGLCaps::dump() const {
     r.appendf("Vertex array object support: %s\n", (fVertexArrayObjectSupport ? "YES": "NO"));
     r.appendf("Use non-VBO for dynamic data: %s\n",
              (fUseNonVBOVertexAndIndexDynamicData ? "YES" : "NO"));
-    r.appendf("Discard FrameBuffer support: %s\n", (fDiscardFBSupport ? "YES" : "NO"));
     r.appendf("Full screen clear is free: %s\n", (fFullClearIsFree ? "YES" : "NO"));
     r.appendf("Drops tile on zero divide: %s\n", (fDropsTileOnZeroDivide ? "YES" : "NO"));
     return r;
diff --git a/src/gpu/gl/GrGLCaps.h b/src/gpu/gl/GrGLCaps.h
index 0939f80c26..21176d16dd 100644
--- a/src/gpu/gl/GrGLCaps.h
+++ b/src/gpu/gl/GrGLCaps.h
@@ -245,9 +245,6 @@ public:
 
     bool fixedFunctionSupport() const { return fFixedFunctionSupport; }
 
-    /// Is there support for discarding the frame buffer
-    bool discardFBSupport() const { return fDiscardFBSupport; }
-
     bool fullClearIsFree() const { return fFullClearIsFree; }
 
     bool dropsTileOnZeroDivide() const { return fDropsTileOnZeroDivide; }
@@ -332,7 +329,6 @@ private:
     bool fUseNonVBOVertexAndIndexDynamicData : 1;
     bool fIsCoreProfile : 1;
     bool fFixedFunctionSupport : 1;
-    bool fDiscardFBSupport : 1;
     bool fFullClearIsFree : 1;
     bool fDropsTileOnZeroDivide : 1;
 
diff --git a/src/gpu/gl/GrGLDefines.h b/src/gpu/gl/GrGLDefines.h
index 0dbd425f0d..a4dc2f782b 100644
--- a/src/gpu/gl/GrGLDefines.h
+++ b/src/gpu/gl/GrGLDefines.h
@@ -691,6 +691,11 @@
 #define GR_GL_DEPTH_ATTACHMENT               0x8D00
 #define GR_GL_STENCIL_ATTACHMENT             0x8D20
 
+// GL_EXT_discard_framebuffer
+#define GR_GL_COLOR                          0x1800
+#define GR_GL_DEPTH                          0x1801
+#define GR_GL_STENCIL                        0x1802
+
 #define GR_GL_NONE                           0
 
 #define GR_GL_FRAMEBUFFER_COMPLETE                      0x8CD5
diff --git a/src/gpu/gl/GrGpuGL.cpp b/src/gpu/gl/GrGpuGL.cpp
index dc2ef7d84e..78bf8f91cf 100644
--- a/src/gpu/gl/GrGpuGL.cpp
+++ b/src/gpu/gl/GrGpuGL.cpp
@@ -1295,6 +1295,25 @@ void GrGpuGL::onClear(const SkIRect* rect, GrColor color, bool canIgnoreRect) {
     GL_CALL(Clear(GR_GL_COLOR_BUFFER_BIT));
 }
 
+void GrGpuGL::discard(GrRenderTarget* renderTarget) {
+    if (NULL == renderTarget) {
+        renderTarget = this->drawState()->getRenderTarget();
+        if (NULL == renderTarget) {
+            return;
+        }
+    }
+
+    GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(renderTarget);
+    if (renderTarget != fHWBoundRenderTarget) {
+        fHWBoundRenderTarget = NULL;
+        GL_CALL(BindFramebuffer(GR_GL_FRAMEBUFFER, glRT->renderFBOID()));
+    }
+    GrGLenum attachments[] = { GR_GL_COLOR };
+    GL_CALL(DiscardFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments), attachments));
+    renderTarget->flagAsResolved();
+}
+
+
 void GrGpuGL::clearStencil() {
     if (NULL == this->getDrawState().getRenderTarget()) {
         return;
diff --git a/src/gpu/gl/GrGpuGL.h b/src/gpu/gl/GrGpuGL.h
index 6a895750c5..e173aeff71 100644
--- a/src/gpu/gl/GrGpuGL.h
+++ b/src/gpu/gl/GrGpuGL.h
@@ -40,6 +40,8 @@ public:
     GrGLSLGeneration glslGeneration() const { return fGLContext.glslGeneration(); }
     const GrGLCaps& glCaps() const { return *fGLContext.caps(); }
 
+    virtual void discard(GrRenderTarget*) SK_OVERRIDE;
+
     // Used by GrGLProgram and GrGLTexGenProgramEffects to configure OpenGL state.
     void bindTexture(int unitIdx, const GrTextureParams& params, GrGLTexture* texture);
     void setProjectionMatrix(const SkMatrix& matrix,