[Fluxus] Rotation Matrix issue

[Scott]

It looks like the rotation matrix math in dada.h is inconsistent; and
the signs on the sins need to be flipped for the y-axis.

I'm gonna make the change locally. This is an interesting one, since
people probably depend on the existing behavior - but I'm pretty sure
that behavior is incorrect!


On Thu, Mar 19, 2009 at 6:04 PM, Scott <alcoholiday at gmail.com> wrote:
> OK - here's another one that has me scratching my head - and this time
> I looked in the bug tracker before posting.
>
> As far as I can tell - we're a right handed coordinate system, which means:
>
> y
> |
> |
> z-------x
>
> Where the "z" above is coming out of the screen.
> Positive rotations about an axis mean COUNTER-CLOCKWISE (or
> anti-clockwise if you speak British) rotations. That is, 1) rotating
> 45 degrees about x, should push the y-axis in to the +y,+z quadrant
> and 2) rotating 45 degrees about z should push the x-axis into the the
> +x,+y quadrant and 3) rotating 45 degrees about y should push the
> z-axis in to the +z +x quadrant.
>
> Well, doing a little checking, this is what I see:
>
> 1) X - puts y-axis +y, +z quad and puts z-axis -y, +z (AS EXPECTED)
> 2) Z - puts x-axis +x, +y quad puts y-axis -x, +y quad (AS EXPECTED)
> 3) Y - puts x-axis +x, +z quad puts z-axis -x, +z quad (???????? - BACKWARDS)
>
> It has been something like 10 years since I've done any 3D graphics so
> it's possible I'm missing something very basic!
>
> ??
>