Performance and Conclusions
So why don’t we see raytracing right now in games? The problem still is performance. Rendering all these effects through the CPU is not as fast as using special purpose hardware like current graphic cards for the rasterization algorithm. But the evolution of CPUs is fast and comparing the CPU power available for development in 2004 with Q3RT with the CPU power available now is by more than a factor of 4. Intel’s new quad core is out and the efficiency using the same CPU clock rate is about 30% higher then before.
One big advantage of raytracing is that it is perfect for parallelization. As explained in the introduction for every pixel of the image a ray is shot through the 3D scene. So if you render an image with 640×480 pixels, you have about 300,000 rays. Each of them can be calculated independently of the others. This means: The image could be split up into four parts and every core of a quad-core CPU can go ahead and calculate the color values of the image without waiting on any of the others cores for intermediate results. Therefore the scaling of performance with the number of cores in Quake 4: Ray traced with OpenRT on Intel’s quad-core ‘Core 2 Extreme QX6700’ is great. The following benchmarks were taken at a resolution of 256×256 pixels on the Quake 4 map ‘Over the Edge (Q4DM7)’.
Problems
Unfortunately ray tracing does not only offer advantages. Right now there are some performance issues regarding to rendering dynamic, randomized changes of the 3D scene that cannot be precalculated. But research on this topic will continue and in the area of dynamics for skeletal animation (e.g. for player models) there are already promising solutions (http://www.mpi-sb.mpg.de/~guenther/modecomp/).
Future
Ray tracing has the potential to become the widely used rendering technology on desktop computers. The number of CPU cores is increasing and special purpose ray tracing-hardware-prototypes (http://www.saarcor.de/) show impressive results in speed improvement. It is still a long way to playing computer games in graphics like the ‘Lord of the Ring’-movies, but we are getting closer to it.
About the author
Daniel Pohl (http://www.idfun.de/temp/q4rt/Daniel%20Pohl/index.html), 26 years old, has recently completed his study of computer science at University Erlangen in Germany. Right now he is looking for a job in the computer games industry or a sponsor for continuation of his research in the area of ray tracing games.
Editor’s note: our sincere thanks goes out to Daniel for sharing this article with our readers at PC Perspective. Please send him some comments and thoughts on the article, or leave them in our forums. Hopefully Daniel’s research and investigations into ray tracing will produce even more fantastic results!
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