I'm trying to setup forward rendering with additive blending, and I'm running into some problems with blending. I'm getting weird artifacts when I render my lighting pass. The first stage is a depth pre-pass that just outputs ambient light from the pixel shader (and renders any shadeless/special single pass materials). The second stage is multiple forward lighting passes, I only have one directional light setup in the screenshot, but for some reason, when I output anything in the lighting passes, I end up with blue background pixels randomly showing through. I also tested with a lighting shader that just outputs a plain white color, and it still gives artifacts, so I'm pretty sure it's not some sort of weird alpha blending bug. If I just leave my lighting pass disabled, then no artifacts appear. Does anyone have an idea what could be causing these? I've attached a screenshot of the artifacts, and a screenshot from GPU Perf Studio showing my render states.