add hotfix addressing OSX bug in glDrawBuffers

src/ACGL/OpenGL/Objects/FrameBufferObject.cc

@@ -154,6 +154,19 @@ void FrameBufferObject::remapAttachments()
     // end debug
 
     bind(); // glDrawBuffers will get part of the FBO state!
+
+#ifdef __APPLE__
+    // Somehow, Apple's current (OSX 10.7) OpenGL implementation skips over all
+    // GL_NONE entries in the bufferMappings array if the only color attachment
+    // specified is GL_COLOR_ATTACHMENT0.
+    // This however causes that no change from the initial FBO state is
+    // detected when the only color attachment should be assigned to a FragData
+    // location other than 0.
+    // Hotfix: Temporarily set all draw buffers to GL_NONE before setting the
+    // actual configuration:
+    glDrawBuffers(0, (GLenum*)NULL);
+#endif // __APPLE__
+
     glDrawBuffers( maxColorBuffers, bufferMappings );
 
     delete[] bufferMappings;