Re: Additive Blending on a floating point PBuffer

• Subject: Re: Additive Blending on a floating point PBuffer
• From: James Milne <email@hidden>
• Date: Tue, 30 Nov 2004 22:03:01 +0000
• Delivered-to: email@hidden
• Delivered-to: email@hidden

 
On Tuesday, November 30, 2004, at 09:37PM, Ben Blundell <email@hidden> wrote:

>Im not so sure about this. I have managed to blend several polygons that 
>have been processed using Cg on a floating point buffer or so it appears. 
>Essentially, the fragment is processed using Cg in order to calculate its 
>addition to the scene. the algorithm is written so is to reduce the 
>"colours" down towards black which it indeed does. However, trying to see 
>all this visually is pretty much impossible so maybe i've been fooled by 
>the output perhaps? So if it cant blend, i wonder what it is actually 
>doing then? Rounding off maybe? Certainly there is a floating point 
>buffer, floating point textures and such like being loaded, but just not 
>blended?

Everything will work in floating-point up until it tries to blend into the framebuffer. Most hardware, save for the very very latest, will not support blending into a floating-point framebuffer.

If your framebuffer is not floating-point, then your fragment will be clamped to [0...1] and blended 8bit-componentwise with values ranging [0..255], just like a normal fragment. This will probably just introduce clamping/saturation artefacts. Perhaps this is what you have been seeing? Have you been using floating-point textures, but not a floating-point framebuffer?

--
James Milne
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