---

Purpose:

To gain experience in 3D hiddens surface removal and rendering using a simple raytracer.

---

Assignment

Implement the following commands.

observer_position: posX posY posZ or observer: posX posY posZ

coi: coiX coiY coiZ

head_tilt: tilt

hither_yon: hither yon

view_angle: angle or angle: angle

Position the observer in world space and set the viewing parameters: observer position, center-of-interest, head tilt (angle), hither and yon clipping distances, and horizontal half-angle-of-view.

viewport: vxl vxr vyb vyt

Clip and display the visible lines in a viewport on the screen defined by the four parameters. The four values are, in order, x-left, x-right, y-bottom, y-top limits of the world window and screen viewport.

device: keyword

input either the word ``screen'' (for drawing to the screen or a filename to write the image to a file.

PPM File Format:

    P3

    xsize ysize

    255

    r g b r g b r g b r g b .... r g b \n

    r g b r g b r g b r g b .... r g b \n

    r g b r g b r g b r g b .... r g b \n

    r g b r g b r g b r g b .... r g b \n

where r g b are int's between 0 and 255

shadows: 1

calculate shadows

shadows: 0

don't calculate shadows

reflections: 1

calculate reflections

refraction: 1

calculate refracted rays

light_position: x y z

set light source position.

sphere: red green blue cx cy cz radius

Position a sphere in world space of radius radius at location (cx,cy,cy) with color (red,green,blue)

illumination_parameters: ka kd ks exp

set illumination parameters for ambient, diffuse, specular, and specular exponent. Note: this is per sphere.

texture_function: function_name (optional command)

        a function to texture map some shading parameter of the object.

end or <end of file>

Terminates the program

#

Ignore the rest of the line; this is a comment line

Notes

• View calculations

Perform your ray-casting in world space. Initially, you may assume the observer is at the origin looking down the negative Z-axis as in the following diagram:



• To handle the other cases, translate and rotate the objects in the scene based on the observer's position and center of interest (translate the observer to the origin and rotate the center of interest to be along the -Z axis). Then, rotate about Z to handle head tilt.

• To calculate the field of view,

assume that your rays go from
X: -tan(theta) to tan(theta)
Y: ratio*-tan(theta) to ratio*tan(theta), where
ratio = (Vyt - Vyb)/(Vxr - Vxl) 


• When calculating shadows, be careful not to intersect the sphere you're on when going away from it towards a light source, i.e., intersecting it at the point of origin before you ever leave. You can test to make sure the center point of a sphere you're about to intersect is in front of you; You can just skip over the test for the ith sphere, if that's the one you're on; Or you can add some epsilon value that you have to be beyond, before you count it as a real intersection (this can create problems with two touching spheres if you're not careful).

Also, notice that the shadow intersection has to be with the semi-infiinte ray, not the infinite line. That is, the intersection has to be out in front of the point of origin, not behind it.


• You can limit the world data structure to a maximum of 50 objects.
  
  
• You need to create  a procedural texture function for simulating wood objects. If you use any algorithms that you don't create, fully document where they came from. You must also supply an input file for this procedure.
  
  
  
• Defaults: ka = 0.2; kd = .8; ks = 1.0; exp =50; no shadows; no reflections, no refraction
  
  
• The lab should read the commands from standard input or have a button to read an input file. 
  
  

Extra Credit

• 25% for implementing polygon intersections and adding the ability to read in .det files. REQUIRED FOR CMSC 634 STUDENTS
• 15% each for a good attempt at water, fireball, or cloud

Suggestions

Implement features in the following order:
1. Get visibility working using just write a white pixel whenever an object is hit by the pixel ray
2. add intensity calculation and then color.
3. add shadows.
4. add reflections




---

David S. Ebert