Fix xfb mode validation with geometry/tessellation

src/libANGLE/ProgramExecutable.h

@@ -328,6 +328,8 @@ class ProgramExecutable final : public angle::Subject
 
     int getGeometryShaderMaxVertices() const { return mGeometryShaderMaxVertices; }
 
+    GLenum getTessGenMode() const { return mTessGenMode; }
+
   private:
     // TODO(timvp): http://anglebug.com/3570: Investigate removing these friend
     // class declarations and accessing the necessary members with getters/setters.

src/libANGLE/validationES.cpp

@@ -735,6 +735,22 @@ bool ValidateTransformFeedbackPrimitiveMode(const Context *context,
         return transformFeedbackPrimitiveMode == renderPrimitiveMode;
     }
 
+    const ProgramExecutable *executable = context->getState().getProgramExecutable();
+    ASSERT(executable);
+    if (executable->hasLinkedShaderStage(ShaderType::Geometry))
+    {
+        // If geometry shader is active, transform feedback mode must match what is output from this
+        // stage.
+        renderPrimitiveMode = executable->getGeometryShaderOutputPrimitiveType();
+    }
+    else if (executable->hasLinkedShaderStage(ShaderType::TessEvaluation))
+    {
+        // Similarly with tessellation shaders, but only if no geometry shader is present.  With
+        // tessellation shaders, only triangles are possibly output.
+        return transformFeedbackPrimitiveMode == PrimitiveMode::Triangles &&
+               executable->getTessGenMode() == GL_TRIANGLES;
+    }
+
     // [GL_EXT_geometry_shader] Table 12.1gs
     switch (renderPrimitiveMode)
     {