Bug 701269 - Deguarantee that ResizeOffscreenFBO clears its buffers - r=bjacob

content/canvas/src/WebGLContext.cpp

@@ -471,6 +471,8 @@ WebGLContext::SetDimensions(PRInt32 width, PRInt32 height)
 
     // If we already have a gl context, then we just need to resize it
     if (gl) {
+        MakeContextCurrent();
+
         gl->ResizeOffscreen(gfxIntSize(width, height)); // Doesn't matter if it succeeds (soft-fail)
         // It's unlikely that we'll get a proper-sized context if we recreate if we didn't on resize
 
@@ -478,6 +480,9 @@ WebGLContext::SetDimensions(PRInt32 width, PRInt32 height)
         mWidth = gl->OffscreenActualSize().width;
         mHeight = gl->OffscreenActualSize().height;
         mResetLayer = true;
+
+        gl->ClearSafely();
+
         return NS_OK;
     }
 
@@ -669,11 +674,13 @@ WebGLContext::SetDimensions(PRInt32 width, PRInt32 height)
     // Make sure that we clear this out, otherwise
     // we'll end up displaying random memory
     gl->fBindFramebuffer(LOCAL_GL_FRAMEBUFFER, gl->GetOffscreenFBO());
+
     gl->fViewport(0, 0, mWidth, mHeight);
     gl->fClearColor(0.0f, 0.0f, 0.0f, 0.0f);
     gl->fClearDepth(1.0f);
     gl->fClearStencil(0);
-    gl->fClear(LOCAL_GL_COLOR_BUFFER_BIT | LOCAL_GL_DEPTH_BUFFER_BIT | LOCAL_GL_STENCIL_BUFFER_BIT);
+
+    gl->ClearSafely();
 
     reporter.SetSuccessful();
     return NS_OK;

gfx/gl/GLContext.cpp

@@ -1086,8 +1086,10 @@ GLContext::ResizeOffscreenFBO(const gfxIntSize& aSize, const bool aUseReadFBO, c
 
     const bool useDrawMSFBO = (samples > 0);
 
-    if (!useDrawMSFBO && !aUseReadFBO)
+    if (!useDrawMSFBO && !aUseReadFBO) {
+        // Early out, as no FBO resize work is necessary.
         return true;
+    }
 
     const bool firstTime = (mOffscreenDrawFBO == 0 && mOffscreenReadFBO == 0);
 
@@ -1401,20 +1403,11 @@ GLContext::ResizeOffscreenFBO(const gfxIntSize& aSize, const bool aUseReadFBO, c
     }
 #endif
 
-    // We're good, and the framebuffer is already attached, so let's
-    // clear out our new framebuffer; otherwise we'll end up displaying
-    // random memory.  We saved all of these things earlier so that we
-    // can restore them.
-    fViewport(0, 0, aSize.width, aSize.height);
-
     // Make sure we know that the buffers are new and thus dirty:
     ForceDirtyFBOs();
 
-    // Clear the new framebuffer with the full viewport
-    fBindFramebuffer(LOCAL_GL_FRAMEBUFFER, GetOffscreenFBO());
-    ClearSafely();
-
-    // Ok, now restore the GL state back to what it was before the resize took place.
+    // We're good, and the framebuffer is already attached.
+    // Now restore the GL state back to what it was before the resize took place.
     BindDrawFBO(curBoundFramebufferDraw);
     BindReadFBO(curBoundFramebufferRead);
     fBindTexture(LOCAL_GL_TEXTURE_2D, curBoundTexture);
@@ -1422,7 +1415,9 @@ GLContext::ResizeOffscreenFBO(const gfxIntSize& aSize, const bool aUseReadFBO, c
 
     // -don't- restore the viewport the first time through this, since
     // the previous one isn't valid.
-    if (!firstTime)
+    if (firstTime)
+        fViewport(0, 0, aSize.width, aSize.height); // XXX This is coming out in 711642
+    else
         fViewport(viewport[0], viewport[1], viewport[2], viewport[3]);
 
     return true;

gfx/gl/GLContext.h

@@ -742,16 +742,16 @@ public:
           return false;
         }
 
-        if (!aOffscreen->mOffscreenDrawFBO && !aOffscreen->mOffscreenReadFBO) {
-            return false;
-        }
-
         if (!aOffscreen->mSharedContext ||
             aOffscreen->mSharedContext != mSharedContext)
         {
             return false;
         }
 
+        if (!aOffscreen->mOffscreenTexture) {
+            return false;
+        }
+
         fBindTexture(LOCAL_GL_TEXTURE_2D, aOffscreen->mOffscreenTexture);
 
         return true;
@@ -770,7 +770,8 @@ public:
     void SetFlushGuaranteesResolve(bool aFlushGuaranteesResolve) {
         mFlushGuaranteesResolve = aFlushGuaranteesResolve;
     }
-
+    
+    // Before reads from offscreen texture
     void GuaranteeResolve() {
         if (mFlushGuaranteesResolve) {
             BlitDirtyFBOs();
@@ -1053,7 +1054,6 @@ public:
         BindReadFBO(read);
     }
 
-    // Before reads from offscreen texture
     void fFinish() {
         BeforeGLReadCall();
         raw_fFinish();
@@ -1423,8 +1423,9 @@ protected:
     void UseBlitProgram();
     void SetBlitFramebufferForDestTexture(GLuint aTexture);
 
-    // helper to create/resize an offscreen FBO,
+    // Helper to create/resize an offscreen FBO,
     // for offscreen implementations that use FBOs.
+    // Note that it does -not- clear the resized buffers.
     bool ResizeOffscreenFBO(const gfxIntSize& aSize, const bool aUseReadFBO, const bool aDisableAA);
     bool ResizeOffscreenFBO(const gfxIntSize& aSize, const bool aUseReadFBO) {
         if (ResizeOffscreenFBO(aSize, aUseReadFBO, false))
@@ -1451,8 +1452,11 @@ protected:
     // Clear to transparent black, with 0 depth and stencil,
     // while preserving current ClearColor etc. values.
     // Useful for resizing offscreen buffers.
+public:
     void ClearSafely();
 
+protected:
+
     nsDataHashtable<nsVoidPtrHashKey, void*> mUserData;
 
     void SetIsGLES2(bool aIsGLES2) {