Re: [Glsdk-devel] [GLM] open questions with the matrix api

[H. H. <hen...@gm...>]

Another open issues has came up:

Do you think we should allow something like this:

glmMatInverse2f (&mat, &mat);
glmMatTranspose2f (&mat, &mat);
glmVecAdd2f (&vec, &vec, &vec);

For some functions, this add some additional processing since it needs to
store temporary values of matrix members before performing an operation,
such as:

GLMmat2f *
glmMatInverse2f (GLMmat2f *out, const GLMmat2f *m)
{
  GLfloat m00, m01, m10, m11;
  GLfloat inv_det;

  assert (out);
  assert (m);

  inv_det = glmMatDeterm2f (m);

  m00 = m->m00;
  m01 = m->m01;
  m10 = m->m10;
  m11 = m->m11;

  out->m00 =   m11 * inv_det;
  out->m01 = - m01 * inv_det;
  out->m10 = - m10 * inv_det;
  out->m11 =   m00 * inv_det;

  return out;
}

We could allows this for simplicity or we could provide additional
entry-points such as:

glmMatInverseSelf2f (&mat);
glmVecAddSelf2f (&vec1, &vec2); // vec1 += vec2

// not allowed and undefined:
glmMatInverse2f (&mat, &mat);
...


My proposal is that we allow glmMatInverse2f (&mat, &mat) and live with the
additional overhead. -Self funcs may still be included for convenience (at
some later GLM versions).


On Sun, Aug 24, 2008 at 9:32 PM, Henri Häkkinen <hen...@gm...> wrote:

> Actually, yes, you are absolutely correct. So
>
>   glmMatSet3f (&mat, &a, &b, &c);
>
> should construct
>
>   | a.x b.x c.x |
>   | a.y b.y c.y |
>   | a.z b.z c.z |
>
> Got it!
>
>
>
> On Sun, Aug 24, 2008 at 8:47 PM, Branan Riley <br...@gm...> wrote:
>
>> I believe OpenGL defines a matrix constructed from vectors like this:
>> | a.x b.x c.x |
>> | a.y b.y c.y |
>> | a.z b.z c.z |
>>
>> We should do the same for consistency.
>>
>> Branan
>>
>> On Sun, Aug 24, 2008 at 9:27 AM, Henri Häkkinen <hen...@gm...>
>> wrote:
>> > There are some open questions in the mathlib's matrix api and I would
>> like
>> > to hear your opinions.
>> >
>> > Do the matrices need member-wise constructors? For example, do we need
>> > something like this:
>> >
>> > GLMmat2f mat;
>> > glmMatSet2f (&mat, 1.0f, 2.0f, 3.0f, 4.0f);
>> >
>> > I suppose the user never needs to do anything like this, instead they
>> use th
>> > higher level entry-point such as Identity and Rotate.
>> >
>> > However, there might be a need for constructing matrices from vectors.
>> >
>> > GLMvec3f a, b, c;
>> > GLMmat3f mat;
>> > glmMatSet3f (&mat, &a, &b, &c);
>> >
>> > At the moment, I have these entry-points and the matrices are
>> constructed
>> > 'column-wise'. For example, the previous code creates this kind of
>> matrix:
>> >
>> > | a.x a.y a.z |
>> > | b.x b.y b.z |
>> > | c.x c.y c.z |
>> >
>> > Should the matrices be build row-wise instead? There is an advantage in
>> > this, as matrix rows define the coordinate axes in a 3D coordinate
>> space.
>> > However, OpenGL defines the matrix memory layout as column-wise, so I
>> guess
>> > it is a kind of more logical to build them column-wise from the vectors.
>> >
>> > --
>> > Henri 'henux' Häkkinen
>> >
>> >
>> >
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>
>
>
> --
> Henri 'henux' Häkkinen
>
>


-- 
Henri 'henux' Häkkinen