mad_murdock

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GPU.
Softshadows from my understanding is the smoothing of the edges around the shadow to make it more real looking, versus the more blocky fixed shadows.
 

BigMac

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That soft shadows is about smoothing of the edges around a shadow is kind of obvious, why else call it smooth? However there is a little more to it than just that. Why are shadows often soft in real life? The only occurrance of a "hard" shadow is when you have a point ligh source. If the source of light is more than a point (a light bulb for instance) then soft shadows come in to play (if you're close enough to the source). Furthermore when having multiple (non point) light sources, the situation gets even more complex.

If you're interested in stuf like this, you might enjoy this link:
http://www.agdsummit.com/slides/Eric%20Vidal.pdf

The original question though is an interesting one because I'm not too sure (as I'm not an expert) whether the computations for soft shadowing are done on the GPU exclusively, but my bet is yes.
 

mad_murdock

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We read the question, Bigmac was just expanding on what I said, and was probably offering out more info to me, and not just to you.

It's my understanding that soft shadows as a whole is a graphics card feature over a CPU. I myself just upgraded from a AMD64 3800+ Newcastle chip to a AMD64 4800+ toledo chip and saw very little in perfomance gain under Fear and Fear XP. I see a bigger jump in performance when I turn off Soft Shadows and Volumetric Lighting.

That implies to me, that it's more on the video card than the CPU. I thought Toms site had an article on this and some benchmark numbers with shadows on and off.