VMD-L Mailing List

From: John Stone (johns_at_ks.uiuc.edu)
Date: Wed Jul 21 2004 - 09:50:13 CDT

Hi,
  This is a function of whether your graphics board has enough
resources to perform clipping in hardware or not. As an example,
the NVidia boards prior to the GeForce 4 series do clipping with
a hardware trick via their texture units as I recall. They have
a limited number of texture units available, and when the number of
textures and clip planes exceeds a certain number, they fall back
to a slower software-based rendering mode. Most games don't use
clipping planes, so the NVidia cards aren't optimized for this
particular use case. Game oriented cards only support clipping
planes because they are a required feature of the basic OpenGL
standard, and are not optional. Believe me, if they could get
away with it, they would probably just skip implementing things
like clipping planes, polygon stippling, etc. These are things
that CAD-like programs like VMD want, but no game has much use for,
and so the video card companies tend to think of them as extra work,
an afterthought if you will. This leads them to implement these
features with whatever leftover hardware resources are on the
card rather than dedicating logic just for clipping etc.

Anyway, the solution to your problem is to either stay with a smaller
number of clip planes or get a video card that implements all 6
clipping planes in hardware.

Thanks,
  John Stone
  vmd_at_ks.uiuc.edu

On Wed, Jul 21, 2004 at 09:03:44AM +0200, Simon Latapie wrote:
> Hye,
>
> I tried to use the "mol clipplane" command. It works fine, but VMD seems
> to become very slow if I enable all the clip planes. Is it normal ?
>
> --
> Garf 

-- 
NIH Resource for Macromolecular Modeling and Bioinformatics
Beckman Institute for Advanced Science and Technology
University of Illinois, 405 N. Mathews Ave, Urbana, IL 61801
Email: johns_at_ks.uiuc.edu                 Phone: 217-244-3349              
  WWW: http://www.ks.uiuc.edu/~johns/      Fax: 217-244-6078