gimbal lock

when throwing my “3d soft” rendering engine together i’d gotten to the point where i could place an opaque aa triangle on the screen.. i then set up some rotation functions and watched my triangle spin around the y axis.

as i added rotation to more than one axis, i noticed that multiaxis rotation resulted in a locked orbit, though the rotation coefficients did tilt the orbit between poles in relation to the rate of rotation. i’d read about gimbal lock a few days previously but it took someone more experienced to point out that this is what was occuring, as at that point in development i was thinking that perhaps i’d misconceived it.. and a few other possibilities.

i had added rotation to each axis as a sine cosine pair instead of using quaternions. my friend recommended i switch to quaternions.

as i was developing casually, often in less than optimal states of consciousness it was probably around 2am half asleep that, from years of audio dsp (and a few simple 3d graphics, like global terrain generation) that my method was fine without quaternions, what i lacked was a state vector..

so i added the state vector (eg. instead of rotating the triangle by a degree, increment a variable for the rotation amount) and that resumed the anticipated rotation behaviour.

so that’s what gimbal lock looks like, and that’s one way to defeat it without quaternions.