EECS 487

Project 1: Scan Conversion

Overview

In this project you will implement the midpoint line drawing algorithm to rasterize line segments, and also a simple method for scan converting triangles and using barycentric coordinates to interpolate colors. Both algorithms are described in our textbook, Fundamentals of Computer Graphics.

You are given support code for this project and will need to

1. install the jot library (see below),
2. copy the project support code and edit the makefile to indicate jot installation information, and
3. implement the missing functionality.
   

Jot

The support code is based on jot, a collection of C++ libraries that support 3D graphics applications. jot was developed at Brown University, Princeton University, and the University of Michigan, runs on Mac OS X, Windows and Linux, and has been used in a number of research projects, including WYSIWYG NPR. Your first step will be to get the jot source code and compile it. For instructions, click here.


Support Code

Next, copy the project support code to your local machine:

  % scp -r red.engin.umich.edu:/afs/engin.umich.edu/class/perm/eecs487/proj1 .

The C++ source code file p1.C contains this support code. Read through this file to get familiar with it, then implement the following missing functionality:

Lines:

• Render mesh edges as 1-pixel wide white lines using the midpoint line drawing algorithm described in the textbook (Fundamentals of Computer Graphics, 2nd Edition, Section 3.5: Line Drawing). The image of the cow on the left above is an example of this type of rendering (known as "wireframe"). 20 points.
  
• Extend the algorithm to handle the case that colors are stored at mesh vertices. In that case, interpolate colors smoothly along the line segment. We suggest you use an incremental method. (See Section 3.5). 10 points.
  
• Add functionality for clipping the lines before scan converting them. The goal is to discard any line segment that lies entirely outside the window, and trim line segments that lie partially outside the window, leaving only the parts that are inside the window. This can greatly speed rendering for some viewpoints. 10 points.
  

Triangles:

• Implement the algorithm described in the text (section 3.5) for scan converting triangles and using barycentric coordinates to interpolate colors assigned to mesh vertices.  25 points.
  
• If the mesh does not have colors assigned to its vertices, compute a single color for the whole triangle using a simple shading calculation: construct a greyscale color value from the dot product of the triangle normal and the vector from the camera to the triangle centroid (both unit vectors). 15 points.
  

Transparency:

• Add the ability to toggle between opaque and semi-transparent lines and triangles. When semi-transparent mode is on, blend the computed color with the color already stored at that pixel in the image, using a blend factor of 0.5. 10 points.

Code quality:

1. Comment your code reasonably, particularly your design decisions and choice of approach.
   
2. Modularize your code: use a suitable number helper functions with descriptive names.
3. Use descriptive variable and function names: apply a suitable tradeoff between symbol-length and descriptiveness.

    Bottom line: Make your code readable! 10 points


Modifying the code:

Implementation of the missing functionality must begin within bodies of two functions with the following prototypes:

  void scan_convert_faces(CGELlist& gels, RefImage& img, double opacity);
  void scan_convert_edges(CGELlist& gels, RefImage& img, double opacity);

You will find these prototypes at the top of p1.C and skeletal definitions somewhere within p1.C. You starting points are marked with the comment: // YOUR CODE HERE

Declare and define helper functions as you see fit.


Building and running the code:

Edit the provided Makefile to define the path to your jot directory. Then you should be able to compile the program, as follows:

  % cd proj1
  % make

This results in an executable named p1 which takes a model file as a command-line argument, for example:

  % p1 models/house.sm