## COM1370 Summer 2003 Quiz 2 review - Prof. Futrelle

### Quiz to be given on Thursday 14 August - Closed book/notes

The focus of this quiz will be on the Gouraud and Phong shading. These are techniques that allow a collection of facets on a object to have their rendered colors and brightness blend smoothly together, "erasing" the boundaries between them.

There are just two sections of your textbook that you need to study: Secs. 16.2.4 and 16.2.5. Read other parts of the text as needed to help you understand these two sections. Also study the plates II.21 through II.32, especially II.31 and II.32.

I will review the material further on Wednesday 8/13, the first day I'll be back from my travels. The next Monday, 8/18, the last day of classes, I'll review for the Final Exam. I'll also have material for Final Exam review posted by that Monday.

There will be no Java code given or required on this quiz.

The quiz will be short, with at most two questions. Below are some typical questions that you should be prepared to answer. Most of the questions will include some type of diagram and you should be prepared to draw diagrams yourself if asked and/or if appropriate. It is conceivable that one of the questions you will be asked is not described in the list below. But you will be able to answer all of the questions I give you if you've read and understood the material, and iff you have practiced drawing some diagrams.

• Given a triangle with brightness values specified at the vertices, draw a diagram and estimate the values along some scan line I will give you. You needn't use a formula to do this, though extra credit will be given if you do apply the one given in the book to the problem.

• Explain how the (average) normals at vertices are computed.

• Extra credit for computing the normal to a surface, given three sequential vertices' x,y,z coordinates (using the determinant form of the cross product). You need not normalize the length of the normal vector you compute. But you should explain why you think the result you get makes sense.

• Give a qualitative explanation of how Phong shading can avoid over-emphasizing a normal that happens to give a strong specular reflection value.

• Give a qualitative explanation of how Gouraud and Phong shading get rid of the appearance of the "seams" between facets. In particular, explain how and why facets differ in appearance if Gouraud or Phong shading is not used.