[Ray tracing can offer amazing graphical renderings, but it is often seen as too computationally taxing for real-time use. In this sponsored article, part of the Intel Visual Computing microsite, Daniel Pohl of Intel's ray tracing group discusses how his team brought their past successes with the technique to Splash Damage's multiplayer shooter Enemy Territory: Quake Wars.]

A scene unfolds in the computer room of a major university. Those watching sense electricity in the air, the kind of tension that builds before a thunderstorm, as a cluster of 20 networked PCs, each equipped with spanking new dual-socket technology and dual processors, warm to the task assigned to them: distributed ray tracing of the game Quake 3 (www.q3rt.de). Though the modest display resolution (512x512) and a frame rate of 20 frames per second (fps) aren't overwhelming by the standards of the day, this doesn't diminish the accomplishment in the least. Special effects never before seen flimmer across the display screen. The viewers watch with rapt attention and a feeling of satisfaction as the intricately rendered images move about the screen. Amazingly, this happened in 2004, a time when most people rejected the concept of real-time ray tracing.

Back to the Future (2008, That Is)

A new research project from the ray-tracing team at Intel advances beyond the 2004 achievements, this time converting the game Enemy Territory: Quake Wars, which was created by id Software and Splash Damage, to use ray tracing. Read on to learn about the development process that followed, the challenges we had to overcome, and the benefits we ultimately achieved-all of which provide valuable insights into the future of ray tracing. To pump up your visual adrenaline level, we've also included numerous images to show the process in action. By the time you finish this article, you'll have a better idea of the ways in which ray tracing can quickly and easily render light and shadow.

Starting From Scratch

For this project, we started rewriting the renderer from ground zero. Because of this, the very first images from the renderer were not of typical ray-tracing caliber, but displayed only the basic parts of the geometry, without any shaders or textures (Figure 1).

Typically, games load their geometry from a variety of different model formats—either created over the in-game map editor or through external modeling tools. Once it is verified that there are no missing objects, the loading of textures can begin. Modern games have their own material description language that allows designers to easily modify texture parameters, blend textures, use bump and specular maps, and write small shader programs. For example, compare the untextured image in Figure 1 with the unlit (Figure 2) and lit (Figure 3) textured images of the same scene.

Today’s games all use a rendering technique called rasterization. Rasterization requires difficult programming work and as many special effects (such as shadows or reflections) need to be calculated as approximations over multiple rendering passes and are often stored in resolution-limited textures in between. These approximations fail in certain cases. Let’s look closer at shadows. With ray tracing, you only need to check if the path from the light to the surface is blocked or not. This can be easily determined with just a ray (the so-called "shadow ray"). If the ray from the light source can reach the surface, the point on the surface is lit. Otherwise, it is in shadow. The gameplay in Quake Wars: Ray Traced takes place primarily outdoors, where the most important light source is sunlight. We were able to apply this form of lighting to the scenes quite easily, and the appearance of the shadows is what one would expect.