Blend option for Multi Render Target has RT index like Blend 0 One One, but the number is different from the attached SV_Target’s index. It looks like the index of AttachmentDescriptor array.
If you assign the AttachmentDescriptor{ color, depthCopy, normal} and start subPass{0,2}, On the shader side, SV_Target0 is the color and SV_Target1 is the normal RT. Blend 0 One One woks for color but Blend 1 One One doesn’t work for normal. You must use Blend 2 One One for normal RT.
Is this by design or a bug of (Native)RenderPass API with Metal’s frame buffer fetch?