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

[Tom Goddard]

Hi Matt,

  First, Chimera VRML rendering of transparent objects is wrong and 
generally not useful.  It simply adds the brightness of all overlying 
surface layers.  Correct behavior dims the appearance of layers in back 
because they are viewed through the layers in front.  The wrong behavior 
gives no cues as to what is in front or in back and results in saturated 
full intensity colors when surfaces are more opaque than transparent.  
The Chimera implementation is just a cheap approximation to correct 
transparency.  The code would have to be much more complex to draw the 
transparency correctly.

  Given that Chimera ignores the depth of VRML surface layers I'm 
surprised it renders slowly.  How does the rendering speed of the 
original volume data in Chimera compare?  I would expect that to be 
slower because it actually resorts the surface triangles by depth each 
time they are drawn.  You can check exact frame rates using the Chimera 
benchmark tool, menu entry Tools / Utilities / Benchmark.  I have plans 
to optimize the rendering of transparent volume surfaces -- I think it 
could be nearly as fast as opaque surfaces with some fancier code.  It 
is unlikely we will make our VRML drawing handle transparency correctly 
since VRML viewing is not a primary function of Chimera.  It might be 
possible to change the VRML implementation to use our volume / molecule 
surface code but many other Chimera projects have higher priority.

    Tom