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CSCE641: Computer Graphics
(due by 12/10/2014)
Homework #4
1. [Rendering]
1.1 Briefly discuss the differences between global illumination and local
illumination. (5%)
1.2 What are the advantages and disadvantages of ray tracing as compared against
radiosity? (5%)
1.3 Briefly explain how photon mapping technique works. (5%)
2. Assume you are at the point (2, 2, 0), looking at a point on the surface at
location (2, 2, 1), which has normal (0, -1, 0). Assume the point is on a surface
with “shininess” value 2, and with coefficient of specular reflection (0.9, 0.0, 0.5).
Assume there is a light at (1,0,3), with color (1.0, 0.7, 0.9). Calculate the specular
component of the lighting. [25%]
3. Assume you are given the triangle ABC, below, and that the texture coordinates
at A are (0.75, 1.0), at B are (1.0, 0.25), and at C are (0.0, 0.0). The texture to be
applied is shown at left. Sketch in the triangle what the triangle would look like
once the texture is applied. Your sketch does not have to be exact or precise, but
should show that you understand the basic process. [20%]
4. Assume you are at the point (2, 6, 3), and are looking in the direction (1, 0, 1).
There is a sphere centered at (4, 3, 9), with radius 5 – i.e. it is described by:
(x-4)2+(y-3)2+(z-9)2-25=0
Assuming you are ray-tracing, compute the point at which the center ray (in the
direction you are looking) intersects the sphere. Show your work, as you would
compute the point in a ray tracing calculation. [25%]
5. For this question, consider radiosity. (15%)
5a) What is progressive refinement (either explain why it is used, or give a very
brief description of how it works)?
5b) How can we use the “Hemicube” to compute the form factor between two
surfaces?
5c) What is the main restriction (i.e., the main assumption made) for the types of
scenes that can be rendered effectively by radiosity?