Posting this question here is a long shot, but if I am lucky someone can
help, by giving new ideas, or maybe by having solved a similar problem
I am developing 3D graphics for a medical application, where grey scale
images from computer X-ray tomography or magnetic resonance are the basic
objects. From these images various volumes like organs and bony structures
are defined. In the 3D display we show these defined volumes, and
additionally one or more grey scale images.
Typically the objects are rendered as triangulated surfaces with a few
thousand triangles, lit and smoothly shaded. No alpha blending is used. The
grey scale images are displayed as texture decals pasted on squares, no
Occasionally, the user wants to rotate the view, and in order to speed up
the display we show everything as non-lit wireframes during the rotation.
Our application runs on DEC AlphaStations. For the graphics, at a
reasonable price/performance level, we use the DEC ZLXp-L1 board (Hardware
acceleration of OpenGL, but not of textures, quite old board), but for new
installations DEC wants us to use the PowerStorm 4D20 (No hardware
acceleration at all), since on fast machines (like the AlphaStation 500)
the 4D20 board performs as good as or better than the ZLXp-L1, and 4D20 is
Our problem is that we do not get the performance we should from the 4D20.
If we use a small test program just doing the display described above, the
two boards are roughly equal in performance (as a matter of fact the 4D20
is much faster in the wireframe mode; when the texture image is included
the ZLXp-L1 is faster since the CPU does the texture at the same time as
the board does the rest). But within our large medical application the 4D20
performance is much, much slower than the ZLXp-L1 and much slower than for
the stand alone test program, eventhough everything else in the
configuration is the same!
We cannot find the reason for this performance difference: In a small
program the 4D20 performance is good , but in a large application the speed
is lost. The large application has allocated 5 - 10 widgets, and several X
pixmaps. However, we cannot detect any swapping between the board and the
main RAM or something similar. And it seems like it is the triangulated
volumes that cause the trouble, the texture image takes roughly the same
time for all cases.
Furthermore, we are not able not obtain a double buffered 24-bit visual on
the 4D20, only a 12-bit double buffered or a 24 bit single buffered one.
We are running under OpenVMS 6.1, DEC Open3D 3.3(?). (OpenVMS is the reason
for why we cannot use PowerStorm 4D40T,50T,60T).
A hint on why our large application slows down the PowerStorm 4D20, anyone?
Any help is appreciated, thanks.