| OCR Text |
Show 55 allocated and initialized. The final step before tracing rays is to create the output file. Normally this is simply an RLE file, but another version of the program, XPRT, creates a window under the X window system[20,42]. XPRT draws a wireframe representation of the scene before it starts rendering pixels. This allows comparing the scene generated to the expected result, and has proven an invaluable debugging tool. 5.3.3 Tracing rays All rays originate from the module implementing the pixel thresher. A ray is first assigned a random time and jitter table indices for motion blur and distributed ray tracing effects. It then passes to the illumination module. The illumination model proceeds as follows: 1. See if the ray hits anything. If not, return. 2. If it did hit the surface, look up the texture map information for the surface at this point. 3. If the coverage is zero, invoke illumination at a ray starting at the hit point and in the same direction. 4. See if the point on the surface hit is in shadow (perturbing the "shadow feeler" if the light has a radius). If it is, find the amount (coverage/transmission) of light that is blocked. 5. Find the diffuse and specular shading components. Modulate them by the shadow value. 6. Color the result to have the surface color, using the texture map values if the surface has a texture map. ¥/hen values are looked up in the texture map, |
