Hi Pierre,
I wrote some code for just that purpose not so long ago:
inline void matrix::SetRotation (const vector &axis, f32 radians)
{
f32 s, c, t;
Maths_SinCos(radians,s,c); // Calculate
sin and cosine
t = 1 - c;
assert(axis.IsValid());
f32 txy = t*(axis.x * axis.y);
f32 tyz = t*(axis.y * axis.z);
f32 txz = t*(axis.x * axis.z);
f32 xs = axis.x * s;
f32 ys = axis.y * s;
f32 zs = axis.z * s;
_14 = _24 = _34 = _41 = _42 = _43 = 0.0f;
_44 = 1.0f;
_11 = t*(axis.x*axis.x) + c;
_22 = t*(axis.y*axis.y) + c;
_33 = t*(axis.z*axis.z) + c;
_12 = txy + zs;
_13 = txz - ys;
_21 = txy - zs;
_23 = tyz + xs;
_31 = txz + ys;
_32 = tyz - xs;
}
I'm sure you can adapt that code. For 4x4 matrices just extend it:
A B C A B C 0
D E F D E F 0
G H I G H I 0
0 0 0 1
Best regards,
Matt.
> -----Original Message-----
> From: Pierre Terdiman [mailto:p.t...@wa...]
> Sent: Monday, August 21, 2000 17:58
> To: gda...@li...
> Subject: [Algorithms] Rotation about arbitrary axis
>
>
> Hi,
>
> Since I needed a piece of code to do that I searched the web
> and found:
> http://www.iuk.tu-harburg.de/hypgraph/modeling/mod_tran/3drota.htm
>
> I used the final matrix at the bottom of the page, but it
> seems to fail when
> the arbitrary axis actually is the Z axis. The third column
> gets erased
> where it should at least contain a 1. This is obvious when
> looking at the
> provided matrix, since the third column of the third row
> depends on the
> rotation angle - and of course if the input axis already is
> the Z axis, it
> shouldn't.
>
> Now, it sounds normal regarding the underlying method
> (mapping the rotation
> axis to Z, etc). But I wonder whether there's an easy way to
> perform a real
> arbitrary rotation about any arbitrary axis without using
> different code
> paths according to the input axis.
>
> I think it can probably be done by introducing quaternions or better,
> angle-axis, in the story. But err.... maybe there's something simpler.
>
> Pierre
>
>
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