Bug 777028 - WebGL: allow only 16 samplers per program on Mesa - r=jgilbert

content/canvas/src/WebGLContext.h

@@ -1099,6 +1099,7 @@ protected:
     bool mMinCapability;
     bool mDisableExtensions;
     bool mHasRobustness;
+    bool mIsMesa;
 
     template<typename WebGLObjectType>
     void DeleteWebGLObjectsArray(nsTArray<WebGLObjectType>& array);
@@ -2324,6 +2325,24 @@ public:
         return false;
     }
 
+    size_t UpperBoundNumSamplerUniforms() {
+        size_t numSamplerUniforms = 0;
+        for (size_t i = 0; i < mAttachedShaders.Length(); ++i) {
+            const WebGLShader *shader = mAttachedShaders[i];
+            if (!shader)
+                continue;
+            for (size_t j = 0; j < shader->mUniformInfos.Length(); ++j) {
+                WebGLUniformInfo u = shader->mUniformInfos[j];
+                if (u.type == SH_SAMPLER_2D ||
+                    u.type == SH_SAMPLER_CUBE)
+                {
+                    numSamplerUniforms += u.arraySize;
+                }
+            }
+        }
+        return numSamplerUniforms;
+    }
+
     bool NextGeneration()
     {
         if (!(mGeneration + 1).isValid())

content/canvas/src/WebGLContextGL.cpp

@@ -3706,6 +3706,17 @@ WebGLContext::LinkProgram(WebGLProgram *program, ErrorResult& rv)
         return;
     }
 
+    // bug 777028
+    // Mesa can't handle more than 16 samplers per program, counting each array entry.
+    if (mIsMesa) {
+        if (program->UpperBoundNumSamplerUniforms() > 16) {
+            GenerateWarning("Programs with more than 16 samplers are disallowed on Mesa drivers "
+                            "to avoid a Mesa crasher.");
+            program->SetLinkStatus(false);
+            return;
+        }
+    }
+
     GLint ok;
     if (gl->WorkAroundDriverBugs() &&
         program->HasBadShaderAttached())
@@ -5029,7 +5040,6 @@ WebGLContext::CompileShader(WebGLShader *shader)
         nsAutoArrayPtr<char> uniform_name(new char[uniform_max_length+1]);
         nsAutoArrayPtr<char> mapped_name(new char[mapped_max_length+1]);
 
-
         for (int i = 0; i < num_uniforms; i++) {
             int length, size;
             ShDataType type;

content/canvas/src/WebGLContextValidate.cpp

@@ -771,6 +771,9 @@ WebGLContext::InitAndValidateGL()
     }
 #endif
 
+    // Mesa can only be detected with the GL_VERSION string, of the form "2.1 Mesa 7.11.0"
+    mIsMesa = strstr((const char *)(gl->fGetString(LOCAL_GL_VERSION)), "Mesa");
+
     // notice that the point of calling GetAndClearError here is not only to check for error,
     // it is also to reset the error flags so that a subsequent WebGL getError call will give the correct result.
     error = gl->GetAndClearError();