commit e755774407d24be85d764b5f871fe05a699eea42
author Corentin Wallez <cwallez@chromium.org> Thu Jun 01 13:09:57 2017 -0400
committer Commit Bot <commit-bot@chromium.org> Fri Jun 02 18:32:55 2017 +0000
tree 8a17bb9bba95fdf326dce74dd586c8a0c94e6854
parent fff7a7dd138c8d3a6f3046a371d9a62e59e2f8b0

WebGL compatibility: remove UB for draw buffers in the GL backend.

WebGL adds two rules:
 - Fragment outputs declared but not written to should default to black.
 - FBO attachments for outputs not declared in the shader should not be
written to (it is UB in OpenGL ES).

Fix the first one by using the SH_INIT_OUTPUT_VARIABLES compiler
options, and the second one by messing with glDrawBuffers so that the
enabled draw buffers are always a subset of the ones declared by the
shader.

BUG=angleproject:2048

Change-Id: I1d851c190959c1acfc3e41d837e6990aec1d4086
Reviewed-on: https://chromium-review.googlesource.com/521682
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>

src/libANGLE/Framebuffer.cpp

diff --git a/src/libANGLE/Framebuffer.cpp b/src/libANGLE/Framebuffer.cpp
index a2aac1d..2952201 100644
--- a/src/libANGLE/Framebuffer.cpp
+++ b/src/libANGLE/Framebuffer.cpp
@@ -176,7 +176,7 @@
 FramebufferState::FramebufferState()
     : mLabel(),
       mColorAttachments(1),
-      mDrawBufferStates(IMPLEMENTATION_MAX_DRAW_BUFFERS, GL_NONE),
+      mDrawBufferStates(1, GL_BACK),
       mReadBufferState(GL_BACK),
       mDefaultWidth(0),
       mDefaultHeight(0),
@@ -185,7 +185,6 @@
       mWebGLDepthStencilConsistent(true)
 {
     ASSERT(mDrawBufferStates.size() > 0);
-    mDrawBufferStates[0] = GL_BACK;
     mEnabledDrawBuffers.set(0);
 }
 
@@ -202,6 +201,7 @@
 {
     ASSERT(mDrawBufferStates.size() > 0);
     mDrawBufferStates[0] = GL_COLOR_ATTACHMENT0_EXT;
+    mEnabledDrawBuffers.set(0);
 }
 
 FramebufferState::~FramebufferState()
@@ -1243,6 +1243,8 @@
                              &mDirtyColorAttachmentBindings[colorIndex], type, binding,
                              textureIndex, resource);
 
+            // TODO(jmadill): ASSERT instead of checking the attachment exists in
+            // formsRenderingFeedbackLoopWith
             bool enabled = (type != GL_NONE && getDrawBufferState(colorIndex) != GL_NONE);
             mState.mEnabledDrawBuffers.set(colorIndex, enabled);
         }