message: Store color and depth format as statics in rt_ref
diff: @@ -44,6 +44,9 @@ private:
  template <pixel_format ColorFormat, pixel_format DepthFormat = PF_UNSPECIFIED>
  struct render_target_ref
  {
  + constexpr static pixel_format color_format = ColorFormat;
  + constexpr static pixel_format depth_format = DepthFormat;
  +
  using color_type = typename pixel_traits<ColorFormat>::type;
  using depth_type = typename pixel_traits<DepthFormat>::type;
  