INT32GP Tutorial #15: Theory

1. What is an orthographic projection? How does it differ from a parallel projection?
2. The following image represents a wire-frame cube, glutWireCube(1.0), rendered, using an orthographic projection glOrtho(-100,100,-100,100,0.0,500.0), with its centre at the origin (0.0, 0.0, 0.0). We are looking at it down the negative z-axis. Camera attributes were specified as gluLookAt(0.0,0.0,10.0,0.0,0.0,0.0,0.0,1.0,0.0). Give the eye, centre, and up coordinates that will render a similar image of the back of the cube.


3. Sketch the image for a camera position of (50,30,10)
4. Explain how we can see the colour magenta when magenta is not a spectral colour.
5. What is the difference between RGB and CMY colour mixes?
6. What colour does the RGB mix (0,1.0,1.0) specify?
7. Using the CMY colour model, how can I create the following colours.
1. magenta
2. black
3. green
8. In OpenGL, I render a large square with RGB colour (1.0,0.0,0.0), and then render a smaller square (0.0,0.0,1.0) in the centre of the larger square. Describe what I will see.
9. What will I see if I render the squares in the opposite order?
10. What colour results from mixing complementary RGB colours?
11. Specify two complementary colours and show how mixing them creates the resulting colour.
12. Colour dithering cannot be applied to a single pixel. Why?
13. How many different light sources can we specify in OpenGL?
14. In OpenGL, specify an infinitely remote light source located along the vector (3,3,0).
15. Specify the above vector as a homogeneous coordinate.
16. What will happen if we specify an infinitely remote (directional) spotlight?
17. What colour will my green shoes appear in a room lit only by magenta light?
18. Would a perfectly diffuse surface be rough or smooth?
19. Taking distance into account when modelling diffuse reflection may lead to poor results even though the calculations adhere strictly to physical law. Why?
20. Why was the Phong model of reflection introduced?
21. Do you need to specify different surface normals for different light sources? Explain.
22. What colour will a sphere with ambient reflection coefficients of (0.3,1.0,0.8) appear if lit only by ambient light (1.0,0.5,0.2)?
23. What will I see if I render a cube with ambient reflection coefficients of (0.0,1.0,1.0,1.0) onto a black background if it is lit only with ambient light RGBA=(1.0,0.0,0.0,0.0)? What happens if I change the light to RGBA=(1.0,0.0,0.0,1.0)?
24. I want a sphere to appear yellowish under white ambient light. What RGB values should I specify for its surface material?
25. Calculate the ambient reflected light from an object with ambient reflection coefficients of (0.8,0.2,0.1) lit by greenish ambient light (0.15,0.7,0.15).