BU CAS CS 480

Introduction to Computer Graphics

Spring 1997

Programming Assignment 2

Due before class on Thursday, February 20

• Create, display, and manage a polygon's local coordinate frame. Provide a menu, keyboard, or mouse interface that allows the user to change the position and orientation of this local coordinate frame.

• Write your own matrix multiplication routines and use them to rotate, translate, scale, and shear a selected polygon. All transforms should be about the selected polygon's local coordinate frame. Provide an interface that allows the user to control the rotation angle, and to control separately the x and y components of translation, scale, and shear.

  One possible interface would be to use arrow keys to increment/decrement parameters, and the R, T, S, and H keys to choose the affected parameter (rotation, translation, scale, shear).

• Use transformations to animate your polygon. Provide an interface to the animation through the pulldown menu.

The polygon editing tool must run on the SGI, therefore you will need to use one of the SGI workstations in the CGL cluster (unless you have access to an SGI workstation elsewhere).

Your program's source files are to be electronically submitted by using the submit program on cgl. The code you submit should conform with the program assignment guidelines.

Part of your grade for this programming assignment will be based on your giving a short demo (2-3 minutes) in the CGL cluster. You will be expected to talk about how your program works, and we will see how well your program performs on some test examples. Demos will be scheduled 2-5 on the assignment due date.

Start programming early.

Local Coordinate Frames

Rotation, scaling, translation, and shear are applied in the selected polygon's local coordinate frame (not the global coordinate frame). For instance, scaling in the local coordinate system's X direction yields different results for these two local coordinate systems:

Furthermore, the user should be able to position the local coordinate frame anywhere inside or outside the selected polygon:

The location of the coordinate frame determines the center of rotation. Thus the rotation with respect to these two local coordinate frames is quite different:

Extra Credit

1. Create, display, and manage multiple polygons on the screen at the same time. Provide a mouse interface to select among all the polygons, and to add or move vertices. Allow the user to move the selected polygon to the back or front.

2. Read/write your polygons to a text file. In addition to polygon vertices, be sure to store each polygon's local coordinate frame, color, line color, and fill flag.

Test Cases

Page Created: Jan 2, 1997      
Last Modified: Jan 2, 1997
Maintained by: Stan Sclaroff