[Glsdk-devel] Commentary on the math library

[Jason M. <ko...@gm...>]

So, I've taken a little time and looked at the current version of the 
math library. It seems to be coming along quite well, but I do have some 
suggestions for improvement.

- We should have a series of Vec4 functions that treat their inputs as 
normalized quaternions. Basically quaternion multiplication, quaternion 
inverse, and a function to convert quaternions into rotation matrices. 
Enough to use quaternions. Oh, and a function to convert angle/axis into 
a quaternion (and one to go back?). I don't think we need a full-fledged 
quaternion type, as a 4-vector of floats is a 4-vector of floats; it's 
all in how you use it.

- Rename the parameters in the lerp functions. I have always had a 
problem with lerp functions in terms of figuring out which parameter I 
would get with an alpha of 0 and which I would get with an alpha of 1. 
So the idea is to have the lerp parameter names themselves specify which 
way it works. IE: "glmVecLerp3f (GLMvec3f *out, const GLMvec3f **v0*, 
const GLMvec3f **v1*, GLfloat s);" It is much more apparent than if 
s==0.0f, you'll get v0, since it has a 0 in the name. Same goes with v1.

- The names of many of the matrix functions do not intuitively describe 
their results. Take the function "GLMmat3f *glmMatRotateX3f (GLMmat3f 
*out, GLfloat angle);" This can do one of two things. It can overwrite 
the contents of "out" with a rotation matrix about the X axis, or it can 
/multiply/ the contents of out by that matrix. The latter would be the 
typical OpenGL style, but the former is what most math libraries would 
do. However, what about "GLMmat3f *glmMatTranslate3f (GLMmat3f *out, 
GLfloat x, GLfloat y);"? This is a function where it would make some 
sense for it to not overwrite the full contents of "out" (though an 
argument can be made that it should). Or at least, one would expect 
there to be a version of Translate3f that will only change the 2 
positional coordinates of a transformation matrix.

Honestly, I'm not sure what to do about it, or if we should do anything 
at all. If all of the functions have one specific kind of behavior 
(overwrite, say), then at least the library is consistent. It just feels 
weird to me to have a function like "glmMatTranslate3f" that completely 
overwrites the matrix rather than just setting certain fields.

This is more something that bugs me than something I think is wrong.

- All of those Mat3 functions for generating transformation matrices? We 
should have Mat4 versions as well. Since Mat3's cannot easily be 
converted into Mat4's, and Mat4's are full 3D transformation matrices, 
it makes sense to provide full coverage in generating transformation 
matrices at the Mat4 level.

- BTW, is the math library going to provide a matrix stack, or is that 
something for a higher-level library?