FML
Friday 15 January, 2010
What computer sciencese really is about: spending 40+ hours looking for a bug only to find out that this so-called “bug” is caused by somebody else his code. FML
Over the past months I’ve spent countless hours working on my project of Computer Animation (given at UHasselt). In short, I have to make a tennisgame containing realistic animations. One of the tasks is to animate a human skeleton (using Inverse Kinematics) so it can swing his tennis racket back and forth. (And hopefully hitting some balls in the process to.) Over the past few weeks however I couldn’t get this thing to work. All it did was moving the arm somewhere randomly, then keep moving untill it got stuck:
Skeleton preparing his arm to swing. Instead he's bending forward.
Hours and hours I’ve wasted looking for the bug in my code. I read my book several times, checked the original thesis again and again and again, I read course materials from other universities about the same subject and recently I’ve been having e-mail correspondence with my professor. Result: nothing, squadush.
This afternoon however I found out what’s wrong. Take a look at the following line:
plMath::plVectorf result = position.outerProduct(axis);
As any non-math-wizard would expect, calculating the cross product of two vectors simply gives you a new vector, right?
Well, it would if I had written the vector class. Unfortunately, I did not. The implementation for the vector class was written by somebody who works at UHasselt and apparently prefers returning a matrix as the result of a cross product. Add in the fact that C++ simply converted the matrix to a vector (not the one I wanted of course) and my calculations were way off. At least I can continue working on my project now, deadline is next week 
.
