[Chimera-users] graphics performance: amira v. chimera

[Greg Couch]

On Wed, 2 Jul 2008, Matthew Dougherty wrote:

> I loaded a MRC file, isosurfaced it, gave it a transparency around
> 0.48, and generated a vrml in chimera.
> I loaded the vrml into amira.
>
> initial comparison:
> I reloaded the vrml into chimera, I turned off the fog on chimera,
> moving the object around the refresh rate seems to be around 8 fps.
> On amira it seems to be around 24fps.
>
> results:
> The graphics on Chimera seems to be better during the rotation of
> transparent objects:
> full rotation in chimera is flawless,
> full rotation in amira results in flipping of the object (vertices in
> back quantum-ly jump to the front, front vertices go to back, looks
> like a z buffer error) periodically at 180 degrees, making it useless
> for many camera positions.
>
> Any comments or suggestions?

What's wrong with just using chimera?  If it's just that it's too 
slow, then please file a bug report and provide a sample data file.

Typical transparency implementations require that the graphics primitives 
be drawn in a back-to-front order.  It sounds like amira is just drawning 
the primitives in the order in which they are given in the vrml file, so 
the transparency effect is haphazard.  You would probably get better 
results from a dedicated vrml viewer, like Octaga, BS Contact, Flux, 
FreeWrl, etc.  Chimera uses an alternate, 2-pass, transparency technique 
that works well, but is not perfect (except within surfaces, where chimera 
does depth-sort the triangles).

 	Greg Couch
 	UCSF Computer Graphics Lab