Performance drawing stereo dots

[Gavin A. Bell]

Whenever I'm presented with a graphics benchmark, I first do a few
back-of-the-envelope calculations to figure out what kind of
performance to expect.  For this application, I calculate:

Quoted speed of point drawing:  400,000 /second (on GT / GTX)

Desired frames/second:          60
     ... therefore, each frame is 1/60 second, = 17 milliseconds long

Screen Clear speed:             8.2 milliseconds (on GTX)
     ... This is half of the time spent on each frame.

So, half of the time will be spent clearing the screen (on a GTX; I
believe screen clear rates are lower for GT machines, but I don't have
those numbers handy ).  Each frame you should be able to draw a total
of:

(400,000 / 60) * 1/2 = 3,333 points

If you are doing stereo, however, you must draw each point twice,
resulting in only ~1,500 points/frame.

And, as you noted, this assumes that you are doing nothing but drawing
points and clearing the screen; any CPU work, transformations, color
commands, user interaction, etc.  will likely further slow you down.
Profiling your application (using pixie) can be extremely helpful
in finding bottlenecks.

This probably doesn't help much, but it will hopefully help you set
performance expectations in the future.

--gavin
--gavin     (gavin at sgi.com,  (415)335-1024)