CS 551: Introduction to Computer Graphics

Goal: Another "Hello World" program, this one to learn simple OpenGL use.

Assigned: Tuesday, February 8, 2000

Due: Thursday, February 17, 2000

Relevant reading/files/software:

• We continue to use Xforms; here is the XForms documentation. The XForms home page (http://bragg.phys.uwm.edu/xforms) has been down for over a week, but Greg Yukl points out that http://world.std.com/~xforms seems to be a working mirror site.
• We will also use OpenGL (http://www.opengl.org) or the public-domain implementation of OpenGL called Mesa: http://www.mesa3d.org.

Synopsis: A simple flythrough application. Your program will load a polygonal object and allow the user to fly around it, using gluLookAt() to control the viewpoint. You will need to design a form in fdesign that contains:

• An OpenGL canvas in which to display the object (name this canvas myCanvas).
• An XForms "file selector" object to specify the .poly file to be viewed (see below).
• Controls for "driving" the viewpoint around, controlling the position and orientation (e.g., look vector) of the camera.
• Controls for specifying the color of the background and the color of the object.
• A button to toggle between wireframe mode (GL_LINE_LOOP) and filled mode (GL_POLYGON).
• A "Quit" button.

As usual, the single best assignment (measured by ease of use and "extra" features) will earn an 11 (one point extra credit).

Turning in the assignment: Before class starts on Thursday, February 17, you should:

• Verify that your code compiles and runs correctly on sgi-1.unixlab.virginia.edu. We will use this machine for compiling all assignments.
• Write a README file describing (very briefly) what you did and anything you'd like us to notice or know about your demo.
• Verify that the line in your Makefile beginning "SUBMIT =" includes all relevant files. This includes all source code (including header files!), fdesign form files (.fd suffix), your README, and the Makefile itself. You should not include object (.o) files, libraries, or the final executable.
• Type "make submit" in the directory containing your code. You will get mail in return from the CS551 account with a list of the files that were successfully received. Note: this mail will be sent to the address in your "reply-to" field. If you have not specifically set this, mail will be sent to yourlogin@virginia.edu.
• If you submit the assignment multiple times be aware that we will only see the last attempt.

Specifics: We are providing a Makefile, which contains rules for compiling and submitting programs, a C file named gfx.c, which contains code to draw into an Xforms glCanvas, and a header file gfx.h, which contains prototypes for the functions in gfx.c. You will modify the functions in gfx.c, adding code to draw the scene and handle callbacks. You will also create a form in fdesign. Saving that form (as a .fd file) will also create .c and .h files that contain the Xforms library code for creating the form, which you must include in your program via the Makefile. Some special things to notice about the code:

• Your code will need to create a global variable pointing to your form. This pointer is returned from the create_form_* call; the Xforms documentation has details. To make the code in gfx.c work correctly you must name this variable myForm. Your form must include a glCanvas object, which you must name myCanvas.
• Gfx.c contains a function called canvas_expose() which will redraw the canvas when it is created or covered and exposed by another window. After the create_form_* call, you must attach this function to your canvas with the line:
  fl_add_canvas_handler(myForm->myCanvas,Expose,canvas_expose,0);
• The .poly format is almost self-explanatory:
• Number of vertices
• Number of faces
• A list of vertex coordinates and (optionally) normals. You can ignore normals if they are given.
• A list of faces. Each face consists simply of a list of indexes into the vertex list. Triangles list three vertices, quadrilaterals four, etc. NOTE: The vertex indices start with 1, not 0!
• Here are some models in the .poly format.

Advice: Start early! This assignment involves pulling together OpenGL (which most of you have never used) and XForms. Don’t underestimate how long it will take, or the difficulty of debugging the dreaded "black screen" effect.