Re: [Glsdk-devel] Commentary on the math library

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

On Thu, Aug 28, 2008 at 9:52 AM, Henri Häkkinen <hen...@gm...> wrote:
> On Thu, Aug 28, 2008 at 12:32 PM, Jason McKesson <ko...@gm...> wrote:
>>
>> - 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.
>
> I think we should implement full featured GLMquatf type.

You can if you want, but we'll have to support every operation that
Vec4's support on them. So if we have a "UniformVec4f" function for
setting uniforms, we would need a separate "UniformQuatf" function for
setting quaternions. It seems wasteful, especially if we're going to
use Vec4f's for things like colors.

>
>>
>> - 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.
>
> I think we should provide an entry-point for creating 4x4 matrices from 3x3
> matrix and a 3D vector as the last vertical column:
>
> glmMatCompose (&out, &rotation, &translation);
>
> or something similar.

The problem there is that you have to create a mat3x3 just to create
the mat4x4 that you actually want. That seems wasteful and not
entirely obvious to the user.

More importantly, what about the other 3 floats in "out" that are not
being set by this?

I know it's a pain to add another version of all of those functions
(I've done it), but it really is the most obvious, simplest solution.