Terrain Rendering: Performance Issues
- Yon Clipping
- the simplest way to improve performance: enable yon clipping and use
fog to hide the hard visual edge of the clipping plant
- can improve framerate dramatically by avoiding pixel fill
- Visibility
(Occlusion Culling)
- because terrain heightfield geometry is special, you can do visibility
occlusion more easily than in the general case
- paper on
Visibility in Terrains by
James Stewart
- Hybrid dVPS
- a commercial library which does several kinds of occlusion
culling, independent of the scene graph library it is used with
- licensing costs $1 for pure research uses, commercial licensing is
done via a partnership with Criterion
- you can download several demos, which include urban and large-area
terrain scenes
- tried the demo on my machine (P3-800, GeForce2) - interestingly,
although the occlusion culling worked well as shown in wireframe
rendering, it was not significantly faster
- Fillrate
- usually measured in millions of pixels per second (Mpixels)
- how much fillrate is needed for an entirely-drawn window without
overdraw?
- 800x600 @ 60Hz = 29 Mpixels
- 1024x768 @ 60Hz = 48 Mpixels
- 1280x1024 @ 60 Hz = 79 Mpixels
- so, in theory all that's needed for a scene with depth complexity of 1
is a card that does ~100 real-world megapixels
- however, thanks to modern scenes having high depth complexity and
multiple rendering passes, several hundred Mpixels are needed
- Floating-point accuracy and world scale
- Parallel Rendering (high end)
- IEEE Transactions on Visualization and Computer Graphics (TVCG), Vol.
2, No. 3 (Sept. 1996)
RIVA: A Versatile Parallel Rendering System for Interactive
Scientific Visualization
P. Peggy Li, William H. Duquette, and David W. Curkendall
Abstract is online, IEEE membership required to access paper
- 5/99 studied the paper
- implementation was run on two platforms: Cray T3D (256 CPUs) and a
Paragon (512 CPUs)
- despite the massive computational power, they only get 1-3 fps
- can handle a whole planet (spherical data)