Examples: Fixed webgl_tiled_forward.html.

examples/webgl_tiled_forward.html

@@ -233,6 +233,8 @@
 						transparent: tIndex === index ? true : false,
 					} );
 
+					mtl.extensions.derivatives = true;
+
 					mtl.uniforms[ "opacity" ].value = tIndex === index ? 0.9 : 1;
 					mtl.uniforms[ "tileData" ] = State.tileData;
 					mtl.uniforms[ "tileTexture" ] = State.tileTexture;