I am writing because of an effect that I have observed for a long time, but never understood nor got rid of.
When you write to a texture with clearing off, and do the clearing manually with a semitransparent black quad, you get a fade or maotionblur effect. Now I want this effect to be really slow, or lines to make really long trails. Thus I set the transparency of the clearing quad to 1/256. Yet, this doesn’t clear the buffer completely over time. You always end up seeing remainders of the trails or a grey instead of black background.
I remember using an ATI card some years ago, and it didn’t show this effect. So it seems to be a hardware specific thing.
When I change the texture format to A16B16G16R16 (why is it BGR and not RGB in this case?), clearing is always on. When I set it to A2R10B10G10 the effect appears to be less.
Right now I work around this effect by raising the contrast on the result in an extra pass and a color transform.
Any ideas regarding this?
Does anybody know how to perform a 16bit clearing / overwrite (ideally 1/(2^16))?