Quality: resulting image is very realistic – sometimes too realistic ( Figure 4). Quality: resulting image is not very realistic. Speed: slow unsuitable for real time process (at least not until we got a 500Ghz machine). Speed: very fast compared to ray-tracing suitable for real time process. (That is roughly 200 times slower than ray-casting.) For instance: on a 320×200 display resolution, a ray-tracer needs to trace 320×200 (64,000) rays. Principle: each ray is traced separately, so that every point (usually a pixel) on the display is traced by one ray. For instance: on a 320×200 display resolution, a ray-caster traces only 320 rays (the number 320 comes from the fact that the display has 320 horizontal pixel resolution, hence 320 vertical column). Principle: rays are cast and traced in groups based on some geometric constraints. (GAME PROGRAMMERS/GAME DEVELOPERS PERSPECTIVE) Ray-Casting TABLE 1: A COMPARISON BETWEEN RAY-CASTING AND RAY-TRACING The main point to remember is that there are “less number of rays” to trace in ray-casting because of some “geometric constraints.” Or, it can also be said that ray-casting is a special purpose implementation of ray-tracing. Table 1 is a general comparison between ray-casting and ray-tracing. We would not want to ray-cast arbitrary splines for instance, because it is difficult to find a geometrical constraints on such shapes. If it were not for such constraints, ray-casting will not be feasible. For instance: walls are always perpendicular with floors (you can see this in games such as Doom or Wolfenstein 3D). This is possible because ray-casting utilizes some geometric constraint to speed up the rendering process. This distinctions because is made because in general, ray-casting is faster than ray-tracing. From game programmers perspective, however, ray-casting is regarded as a special implementation (subclass) of ray-tracing. Indeed, some books use both terms interchangeably. Like ray-casting, ray-tracing “determines the visibility of surfaces by tracing imaginary rays of light from viewer’s eye to the object in the scene” (Foley 701).įrom both definitions, it seems that ray-casting and ray-tracing is the same.
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