Computer Graphics Fall 2010 group home

Homework 4, Email to Peter by Sep 30

1. Extend the paint program presented in class as follows. Hand in the code and screendump(s) showing the new functionality. Document anything that is unclear.
   1. (10 points) Add 3 more colors of your choosing.
   2. (10) Add a main menu entry and submenu to enable or disable writing with XOR instead of with copy.
   3. (10) Add an entry to the permanent menu on the top to draw a circle; the user selects opposite ends of a diameter.
   4. (10) Modify the program to keep drawing primitives until you select something else from the top menu. That is, after you click on line, each pair of future clicks causes another line. (Now the program ignores left clicks after the first 2 until you again select something on the top menu.)
   5. (20) Modify the program to use a display list, so that the objects are redrawn when you redisplay the window. (This may be surprisingly hard.)
2. (5) Why does paint.c contain this line:
   y=wh-y;
3. (15) Assume that you have a model coordinate space with corners (-100,-100) and (100,200). You wish to map points in it to a window with corners (0,0) and (1,1). (0,50) should map to (0.5,0.5). X and Y should scale the same. Compute what the transformations for X and Y should be, in this form:
   X' = s X + dx
   Y' = s Y + dy
   I.e., tell me what s, dx, and dy are.
   
4. (5) What is the difference between a Motion callback and a PassiveMotion callback?
5. (5) How can glutPostRedisplay make your program a little more efficient?
6. (5) When creating a menu, when would you need to store the menu id that is returned?
7. (5) Since a menu has only one callback, which is called regardless of which item you click on, how does the callback know which item you clicked on?
8. (10) Edit alpha.c to remove the line that enables GL_BLEND, compile and run. Report on how the output is different.