Adding More Special Effects

In our ray-tracing conversion, once we reached the same quality as the original game, we began adding enhancements and more special effects. Ray tracing does a very good job with reflections and refractions. The most common everyday objects in the world that exhibit this behavior are glass and water.

Glass

A large dome exists in the original game. We changed the surface properties of the dome so that it would appear to be made out of glass (Figure 8). Using the refraction index for glass (which you can find in your favorite physics books), we wrote a shader to accurately depict the reflections and refractions. The code is about 15 lines long in our HLSL- like ray-tracing shading language and generates very pleasing results.

Water

Rendering water can be accomplished different ways. We investigated two approaches: water on a 2D surface and water with genuine 3D properties (Source: Implementation by Jacco Bikker).

To render the water in 2D, we used a bump map to simulate waves [Figure 9(a)]. The 3D water image uses a mesh with around 100,000 triangles in several subgrids [Figure 9(b)]. Those subgrids are updated every frame, depending on their visibility. (During rendering, subgrids that are not visible are ignored.) The visibility test is performed over rays.

The Performance Issue

Performance is the main reason why ray tracing is not yet used in mainstream games. Compared to special-purpose rasterization graphics hardware—such as current-generation GPUs—ray tracing is fairly slow. Also, a lack of texture units for our CPU-based approach to ray tracing causes significant slowdowns when trilinear filtering is used for all texture samples. With Intel’s latest quad-socket systems—equipped with a 2.66 GHz Dunnington processor in each socket—we can achieve approximately 20 to 35 fps at a resolution of 1280x720. Nonetheless, this represents a significant improvement over the experiments in 2004 that required 20 machines to render a simpler game more slowly and at a lower resolution. The greatest performance gains result from research efforts around the world that improve efficiency and the new, many-core hardware platforms that use parallelism to accelerate graphics operations.

The Future of Ray Tracing

As mentioned earlier, creating very realistic shadows in games is not an easy task. Given the current state of our demo work, only hard-edged shadows are produced. Modern games tend toward soft shadows, which usually require many more rays. This important topic deserves more study; smarter approaches to this task need to be developed. Also, to obtain higher quality images, better anti-aliasing methods are needed. Adaptive super-sampling is a smart way of refining the rendering of the scene at those exact places where it will deliver the greatest benefit. There are experimental implementations, but they need to be tested and tuned for the best results. With the industry moving from multi-core to many-core (that is, greater than ten cores), improving the algorithms so they can fully use the newly acquired power will be interesting.

Even though Intel’s upcoming many-core graphics architecture, code named Larrabee, has been primarily developed as a rasterizer card, it will also be freely programmable. This opens up some extremely interesting opportunities to perform ray tracing with the Larrabee architecture.

Stay tuned for more information about our upcoming ray-tracing projects!