Make shading of CAOs optional (#10033)

client/shaders/object_shader/opengl_vertex.glsl

@@ -39,11 +39,15 @@ void main(void)
 	lightVec = sunPosition - worldPosition;
 	eyeVec = -(gl_ModelViewMatrix * gl_Vertex).xyz;
 
+#if (MATERIAL_TYPE == TILE_MATERIAL_PLAIN) || (MATERIAL_TYPE == TILE_MATERIAL_PLAIN_ALPHA)
+	vIDiff = 1.0;
+#else
 	// This is intentional comparison with zero without any margin.
 	// If normal is not equal to zero exactly, then we assume it's a valid, just not normalized vector
 	vIDiff = length(gl_Normal) == 0.0
 		? 1.0
 		: directional_ambient(normalize(gl_Normal));
+#endif
 
 	gl_FrontColor = gl_BackColor = gl_Color;
 }