It may sound simple but…
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Is there a speed difference on nowadays’ hardware between rendering a normal triangle and a blended triangle ?
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Is there a speed difference when using GL_MODULATE against GL_DECAL ?
Y.
It may sound simple but…
Is there a speed difference on nowadays’ hardware between rendering a normal triangle and a blended triangle ?
Is there a speed difference when using GL_MODULATE against GL_DECAL ?
Y.
Sorry,I can only answer your first question:
If you have a card which is able to do multitexturing(voodoo2,tnt,…) the texture and the blended one can be drawn in one single pass,which means there is nearly no performance-loss.On cards which aren´t able,you´ll have to do this with two single passes(first the texture,than the other texture to blend).Which means that on these cards you´ll only get half the performance with blending.
HTH,XBTC!
Ok, thanks for the answers… but:
If not considering multi-pass, do you know a ratio of speed difference between normal/blend rendering ? I just want to know if it’s a lot slower, or if the difference is hardly noticable.
So, what’s exactly the interest of using GL_DECAL…?
Y.
i’d say blended rendering is twice slower than normal, because of the memory accesses involved.
probably mults are hardwired, maybe with a barrel multiplier, don’t know exactly: so they are pratically free.
i suppose memory access is the heavy task.
about decals… effectively i never made use of it, just tested, and found it is much the same as modulate. now i give a look to the red book… wait… no it is not.
by the functions i see GL_DECAL mode isn’t influenced by the previous color fragment, so a decal is… well… a decal
it appears on the surface with it’s color, and is not modulated with primitive lighting results.
Dolo//\ightY
[This message has been edited by dmy (edited 05-23-2000).]