I think you have to conceptualize how diffusion models work, which is that once the green triangle has been put into the image in the early steps, the later gen

I think you have to conceptualize how diffusion models work, which is that once the green triangle has been put into the image in the early steps, the later generations will be influenced by the presence of it, and fill in fine details like reflection as it goes along. The reason it knows this is that this is how any light in a real photograph works, not just CGI. Or if your prompt was “A green triangle looking at itself in the mirror” then early generation steps would have two green triangle like shapes. It doesn’t need to know about the concept of light reflection. It does know about composition of an image based on the word mirror though.