[Chimera-users] mac pro theoretical question

Tom Goddard goddard at cgl.ucsf.edu
Tue Jan 29 16:33:15 PST 2008

Hi Jeff,

  I don't know much about any of the current Apple graphics cards 
(Radeon HD 2600 XT 256Mb, Nvidia GeForce 8800 GT 512Mb, Nvidia Quadro FX 
5600 1.5Gb).  My first concern would be whether bugs in the drivers for 
these cards are going to cause trouble in Chimera.  We have a web page 
that lists problems with graphics drivers observed using Chimera:


There was a recently reported problem (squashed atom spheres) with 
GeForce 8800 GTX (not GT) on Windows.  The Apple driver may be much 
different.  The Quadro FX 4500 which was Apple's high-end offering 
before the 5600 crashed with solid volume rendering.  Don't know if the 
current 5600 would have the same problem -- but there is a fair chance 
it does.  Chimera uses many different OpenGL calls and I'd guess 1 in 10 
drivers exhibit bugs of varying severity when using Chimera.

  Some of Chimera performance is related to graphics card speed and 
memory, and some is related to CPU speed and memory.  When the displayed 
models rotate slowly that is the graphics card except if you are using 
transparent volume surfaces or meshes which are sorted by depth on the 
CPU for every new view angle.  Everything else is the CPU, main memory, 
memory cache performance, and hard-drive speed.

  Solid style volume rendering makes a lot of textures which usually 
will be stored in graphics card memory.  More graphics card memory could 
make larger volume rotate faster because they fit on the card.  256^3 
volumes (16 million voxels, 4 bytes per voxel) typically rotate at 10 
frames per second with graphics memory sizes 128 Mb and up.   Textures 
have to have power of 2 sizes so just knowing that can get you better 
performance if you trim your 550x550x100 region to 512x512x100 you'll 
get a factor of 4 speed-up.

  I don't know if a single application using one display can use more 
than one graphics card in Apple's multicard options.  Chimera has no 
special code to do that.

  For large volume data, hard-drive speed, main memory size, and CPU 
speed are likely to be noticable factors in Chimera performance, each of 
about equal importance to graphics card speed.


> hi Tom,
> if you were considering a Mac Pro at some point in the future, what 
> graphics card would you pick when thinking of chimera (if you don't 
> mind peeking at some point at the list at 
> http://store.apple.com/1-800-MY-APPLE/WebObjects/AppleStore.woa/9354001/wo/Gd396p47oXEG3YxkIQUaeKq85Yd/5.?p=0 
> are rendering bottlenecks in chimera largely a processor-limited thing 
> (and thus one of the 'lower end' cards listed would be fine), or 
> something that benefits dramatically from spending $2000 on a graphics 
> card (I am not in that kind of market, just wondering what kind of 
> decision you would make if evaluating that platform)
> best,
> -Jeff

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