Project 3: Ray Tracing

Objective

Scene Description Language

fov  angle

Specifies the field of view (in degrees) for a perspective projection. The viewer's eye position is assumed to be at the origin and to be looking down the negative z-axis (giving us a right-handed coordinate system). The y-axis points up.

background  r g b

Background color. If a ray misses all the objects in the scene, the pixel should be given this color.

light  x y z [r g b]

Point light source at position (x,y,z). Its color is optional (the default is white). Your code should allow up to 10 light sources. Any objects in your scene should cast shadows from these light sources, of course.

surface  Kar Kag Kab  Kdr Kdg Kdb  Ksr Ksg Ksb  N  Krefl

This command describes the reflectance properties of a surface, and this reflectance should be given to the objects that follow the command in the scene description, such as spheres and cylinders. The first three values are the ambient coefficients (red, green, blue), followed by diffuse and specular coefficients. Next comes the specular power N (the Phong exponent), which says how shiny the highlight of the surface should be. The final value is the reflection coefficient (0 = no reflection, 1 = perfect mirror). Usually, 0 <= Ka,Kd,Ks,Krefl <= 1.

sphere  x y z radius

A sphere with its center at (x, y, z).

cylinder  x y z  height  radius

A vertical cylinder with the center of its base at (x,y,z) and a given height and radius. This command will only allow us to make cylinders that have an axis parallel to the y-axis.

write  filename[.ppm]

Ray-traces the scene and saves the image to a PPM image file.

Code Provided

The second set of routines that we provide are for writing a pixel in a window and for writing an image to a file. You used these routines for your first assignment. There are just a few routines that you'll need to use:

gtBeginGraphics (xsize, ysize);

This command creates a framebuffer of the given size. If you are linking to the SGI routines, this actually creates a window on the screen. If you are on a different kind of workstation, it simply allocates the necessary memory.

gtWritePixel (x, y, r, g, b);

This command writes a pixel to the screen at integer locations (x,y). The color of the pixel is (r,g,b), where these are integers from 0 to 255 for each of red, green and blue.

gtWriteFramebuffer(filename);

Write the contents of the framebuffer to a PPM file.

gtEndGraphics();

Deletes the framebuffer.

CLI Routines

  COMMAND ("sphere  x y z radius") {
    float x,y,z;
    float radius;
    get_real (&x);
    get_real (&y);
    get_real (&z);
    get_real (&radius);
    create_sphere (x, y, z, radius);  /* your own sphere-creation code */
  }

Scene Files

Sample Results:

Suggested Approach

Once the shell of the program is ready, we suggest creating the main loop that creates the primary rays (those from the eye). Start by printing out the information about these rays to make sure that the numbers make sense. Once you've got this loop working, then start on the ray/sphere intersection routine. Don't bother shading the sphere correctly at first-- just color it anything other than the background color. Once you've got a round object on the screen, then work on the shading of the sphere. Finally, work on ray/cylinder intersection.

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