Bug 775843 - Always BindAttribLocation something to attrib 0 if possible. r=jgilbert

content/canvas/src/WebGLContext.h

@@ -872,6 +872,7 @@ private:
     void VertexAttrib4fv_base(WebGLuint idx, uint32_t arrayLength, const WebGLfloat* ptr);
 
     bool ValidateBufferFetching(const char *info);
+    bool BindArrayAttribToLocation0(WebGLProgram *program);
 
 // -----------------------------------------------------------------------------
 // PROTECTED

content/canvas/src/WebGLContextGL.cpp

@@ -1966,6 +1966,36 @@ WebGLContext::IsTexture(WebGLTexture *tex)
         tex->HasEverBeenBound();
 }
 
+// Try to bind an attribute that is an array to location 0:
+bool WebGLContext::BindArrayAttribToLocation0(WebGLProgram *program)
+{
+    if (mBoundVertexArray->mAttribBuffers[0].enabled) {
+        return false;
+    }
+
+    GLint leastArrayLocation = -1;
+
+    std::map<GLint, nsCString>::iterator itr;
+    for (itr = program->mActiveAttribMap.begin();
+         itr != program->mActiveAttribMap.end();
+         itr++) {
+        int32_t index = itr->first;
+        if (mBoundVertexArray->mAttribBuffers[index].enabled &&
+            index < leastArrayLocation)
+        {
+            leastArrayLocation = index;
+        }
+    }
+
+    if (leastArrayLocation > 0) {
+        nsCString& attrName = program->mActiveAttribMap.find(leastArrayLocation)->second;
+        const char* attrNameCStr = attrName.get();
+        gl->fBindAttribLocation(program->GLName(), 0, attrNameCStr);
+        return true;
+    }
+    return false;
+}
+
 void
 WebGLContext::LinkProgram(WebGLProgram *program)
 {
@@ -2003,7 +2033,8 @@ WebGLContext::LinkProgram(WebGLProgram *program)
         return;
     }
 
-    GLint ok;
+    bool updateInfoSucceeded = false;
+    GLint ok = 0;
     if (gl->WorkAroundDriverBugs() &&
         program->HasBadShaderAttached())
     {
@@ -2015,12 +2046,25 @@ WebGLContext::LinkProgram(WebGLProgram *program)
         MakeContextCurrent();
         gl->fLinkProgram(progname);
         gl->fGetProgramiv(progname, LOCAL_GL_LINK_STATUS, &ok);
+
+        if (ok) {
+            updateInfoSucceeded = program->UpdateInfo();
+            program->SetLinkStatus(updateInfoSucceeded);
+
+            if (BindArrayAttribToLocation0(program)) {
+                GenerateWarning("linkProgram: relinking program to make attrib0 an "
+                                "array.");
+                gl->fLinkProgram(progname);
+                gl->fGetProgramiv(progname, LOCAL_GL_LINK_STATUS, &ok);
+                if (ok) {
+                    updateInfoSucceeded = program->UpdateInfo();
+                    program->SetLinkStatus(updateInfoSucceeded);
+                }
+            }
+        }
     }
 
     if (ok) {
-        bool updateInfoSucceeded = program->UpdateInfo();
-        program->SetLinkStatus(updateInfoSucceeded);
-
         // Bug 750527
         if (gl->WorkAroundDriverBugs() &&
             updateInfoSucceeded &&

content/canvas/src/WebGLContextValidate.cpp

@@ -86,6 +86,25 @@ WebGLProgram::UpdateInfo()
         }
     }
 
+    mActiveAttribMap.clear();
+
+    GLint numActiveAttrs = 0;
+    mContext->gl->fGetProgramiv(mGLName, LOCAL_GL_ACTIVE_ATTRIBUTES, &numActiveAttrs);
+
+    // Spec says the maximum attrib name length is 256 chars, so this is
+    // sufficient to hold any attrib name.
+    char attrName[257];
+
+    GLint dummySize;
+    GLenum dummyType;
+    for (GLint i = 0; i < numActiveAttrs; i++) {
+        mContext->gl->fGetActiveAttrib(mGLName, i, 257, nullptr, &dummySize,
+                                       &dummyType, attrName);
+        GLint attrLoc = mContext->gl->fGetAttribLocation(mGLName, attrName);
+        MOZ_ASSERT(attrLoc >= 0);
+        mActiveAttribMap.insert(std::make_pair(attrLoc, nsCString(attrName)));
+    }
+
     return true;
 }
 

content/canvas/src/WebGLProgram.h

@@ -110,6 +110,9 @@ public:
     NS_DECL_CYCLE_COLLECTING_ISUPPORTS
     NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(WebGLProgram)
 
+    // public post-link data
+    std::map<GLint, nsCString> mActiveAttribMap;
+
 protected:
 
     WebGLuint mGLName;