**COM1370 Computer Graphics --
Midterm Exam -- Wednesday, July 25**^{th}

#### Summer 2001 -- Professor Futrelle

College of Computer Science, Northeastern U., Boston, MA

PRINT your name ____________________________ Your ID no. ___________

**Question 1.**

Assume that a CLUT has a three-bit RGB color index and a three-bit color output.
Draw the CLUT elements that would lead to the production of output color codes that
are complementary to the input, e.g, Red in would produce Blue + Green out.

**Question 2.**

Below are shown the 3D rotation matrices for 90-degree rotations around the
y and z axes.

Compute the two different matrices R_{z} x R_{y}
and R_{y} x R_{z}. These should
be different. Use each of the resultant matrices to transform the point
x=1, y=z=0 and show that the point is transformed differently by the two
matrices.

**Question 3.**

Write out the algebraic details of the DDA algorithm for line drawing.
Be clear which values need to be floating point and how integer values
would also be involved.

**Question 4.**

Show in step-by-step diagrams how the Cohen-Sutherland algorithm would
clip the following line. Explain at what stage the line endpoint labels
are switched and at what stages the region codes are used in the decisions.
You do not have to list the actual binary region codes. Just describe at what
stage you used them to make decisions and what those decisions were.
Use the order Left, Right, Bottom, Top. Hint: You will only need to switch endpoints
once -- don't jump back and forth.

**Question 5.**

Describe how traversing the following triangle results in the construction
of a new clipped polygon, according to the Sutherland-Hodgeman algorithm.
Clip only against the right-hand edge of the window. You are not expected
to know each rule for creating and dropping points, but show that you understand
the basics of the idea.