Support devices without glCopyImageSubData or rendering to RGBAF32 target

[jfizz]

I ran into the edge case referenced in this TODO.

// TODO(gw): We still need a proper solution for the subset of devices
//           that don't support glCopyImageSubData *OR* rendering to a
//           RGBAF32 render target. These devices will currently fail
//           to resize the GPU cache texture.

Has anyone put thought into how this could be accomplished? I am interested in giving it a shot.

[kvark]

I guess you could copy the data to a PBO and then copy from it into the destination, as a workaround. It would be good to first identify the class of hardware where this would be needed.

[jfizz]

I was able to resolve it (in my case anyway) with the following changes to renderer.rs:

let supports_copy_image_sub_data = device.get_capabilities().supports_copy_image_sub_data;
let supports_blit_to_texture_array =
    device.get_capabilities().supports_blit_to_texture_array;
let rt_info = if supports_copy_image_sub_data || supports_blit_to_texture_array {
    None
} else {
    Some(RenderTargetInfo { has_depth: false })
};

Note the new supports_blit_to_texture_array variable. My device supports blit_to_texture_array but not copy_image_sub_data. Since blit_render_target is a fallback for devices which don't support copy_image_sub_data, I think it works out.