Archive for April, 2006

Assignment 9

Friday, April 28th, 2006

Assignment 9 is available. Trust me — the assignment will be easier if you attend class and implement the version of the algorithm that we discuss.

Slides for tonight’s lecture

Saturday, April 15th, 2006

For the second half of tonight’s lecture, we’ll be looking at the Aliasing and Antialiasing slides in the ACM SIGGRAPH 1993 Education Slide Set. There are some visual effects here that I wouldn’t be able to draw on a whiteboard to save my life.

A note on doing the work yourself

Friday, April 14th, 2006

I realize that in Assignment 6 and Assignment 7 where we deal with well-known algorithms, it will be especially tempting to use someone else’s implementation — they are, after all, readily available on teh interwebs.

Note, however, the following:

  1. Turning in code you didn’t write yourself is Academic Dishonesty.
  2. Using someone else’s pseudocode is fine, as long as you credit the source.
  3. If you do use someone else’s pseudocode, make sure you understand what it does.
  4. There will be at least one question on each algorithm on the Final Exam.
  5. If you take the time to implement the algorithm yourself, you will be more likely to remember it well enough to earn full credit on the exam.

Remember also that if you are struggling with an algorithm, you are allowed to work on homework assignments with a partner.

Hint: pick a partner who’s smarter than you are.

Announcements

Saturday, April 8th, 2006

Assignment 6 is available.

Note the updated office hours shown to the left: I’ve been able to rearrange my work schedule in order to be available before class. Be sure to drop by and visit.

GLIntercept

Saturday, April 1st, 2006

Here’s a cool debugging tool for OpenGL on Windows: GLIntercept. You can use it to track every OpenGL function call along with its parameters. (For those of you familiar with UNIX, this is like truss(1) or strace(1), only for OpenGL calls instead of system calls.)

Here’s a 30-second walkthrough:

  1. Download and run the Windows installer. You’ll end up with a new directory, C:\Program Files\GLIntercept0_5.
  2. Copy OpenGL32.dll and gliConfig_FullDebug.ini to the same directory as your program. Rename gliConfig_FullDebug.ini to gliConfig.ini
  3. Run your program. A new file will be created in the same directory called gliInterceptLog.txt, containing every OpenGL call your program makes. (You may also find that your program is a little slower).

Here’s some of the output from running assignment5.c:

glClearColor(0.000000,0.000000,0.000000,0.000000)
wglGetCurrentContext()=0x10000
wglGetCurrentDC()=0xb70114f8
wglGetCurrentContext()=0x10000
wglGetCurrentDC()=0xb70114f8
glViewport(0,0,600,300)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glOrtho(0.000000,2.000000,0.000000,1.000000,-1.000000,1.000000)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glClear(GL_COLOR_BUFFER_BIT)
glColor3f(1.000000,1.000000,0.000000)
glBegin(GL_LINES)
glVertex3f(1.000000,0.000000,0.000000)
glVertex3f(1.000000,1.000000,0.000000)
glEnd()
glViewport(300,0,300,300)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glFrustum(-1.500000,1.500000,-1.500000,1.500000,2.000000,8.000000)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glMultMatrixf([1.000000,0.000000,0.000000,0.000000,
             0.000000,1.000000,0.000000,0.000000,
             0.000000,0.000000,1.000000,0.000000,
             0.000000,0.000000,0.000000,1.000000])
glTranslated(0.000000,0.000000,-6.500000)
glPushMatrix()
glPushMatrix()
glColor3f(1.000000,0.000000,0.000000)
glBegin(GL_LINE_LOOP)
glNormal3fv([0.000000,0.000000,-1.000000])
glVertex3fv([0.500000,0.500000,-0.500000])
glVertex3fv([0.500000,-0.500000,-0.500000])
glVertex3fv([-0.500000,-0.500000,-0.500000])
glVertex3fv([-0.500000,0.500000,-0.500000])
glEnd()

Running with gliConfig_FullDebug.ini also makes sure that every call to an OpenGL function is checked with glGetError(), which will catch things like passing bad values to functions or trying to pop the matrix stack more times that it’s been pushed.

To make the best use of a tool like this, you’ll probably want a utility to tail the log as your program is running. (I’m told there are also GUI versions).

Note that you don’t need access to the source code — if you have a game at home that uses OpenGL, you can watch what it’s doing, too. (Just don’t steal their code, and don’t tell them I’m the one who told you how.)

GLIntercept has a few more tricks up its sleeve, but I’ll leave it up to you to read about them. For Linux people, there’s a similar program called BuGLe, but I haven’t tried it. And, of course, we smug OS X weenies have the OpenGL Profiler.

For those of you using Igloo, I’ve put together a new debug package that includes GLIntercept and Windows port of GNU tail. I’m not entirely sure about the legality of all this — GLIntercept and GNU tail are available under the GNU General Public license, but EiC is still MIA.