Re: [Algorithms] OBBs & Max

[Pierre T. <p.t...@wa...>]

Apparently this issue has been bugging you for a long time now....

Well. I've been using RAPID and MAX together as well, and it just works.
I've never had such troubles - that's also why I was surprised by Kent
Quirk's recent post about the wrong matrix in RAPID.

I export from MAX 3.1 using this, ...
http://www.codercorner.com/Flexporter.htm

...then use my enhanced RAPID version...
http://www.codercorner.com/RAPID_Hack.htm

...packed in my collision detection lib:
http://www.codercorner.com/ZCollide.htm

On a side note, a related link:
http://www.codercorner.com/Gottschalk.htm

It just works. A friend of mine nonetheless, started using RAPID some months
ago now, and reported some problems : collisions weren't detected. We looked
into it, and it appeared he was using an old RAPID version (1.04 I think). I
gave him the last one. He recompiled. And... it just worked like the
proverbial charm. It's been working for months now.

So, to make things clear once and for all, I really think the problem lies
somewhere in your code, not in MAX nor in RAPID. Or maybe you're using an
old RAPID version as well ? I suspect you just feed RAPID with wrong
rotation matrices, even if that's something you must have checked to death
now... Here's the way I use:

Say you matrix is defined as an array of 16 floats:

float   m[4][4];

That matrix is D3D-compliant. That is, I can send that directly to D3D as a
world matrix. Now, here's the rotation matrix to send to RAPID:

float R1[3][3];

Say M1 is a pointer to a D3D-compliant matrix. The transform is:

R1[0][0] = M1->m[0][0];
R1[0][1] = M1->m[1][0];
R1[0][2] = M1->m[2][0];

R1[1][0] = M1->m[0][1];
R1[1][1] = M1->m[1][1];
R1[1][2] = M1->m[2][1];

R1[2][0] = M1->m[0][2];
R1[2][1] = M1->m[1][2];
R1[2][2] = M1->m[2][2];

In other words, you must transpose the rotation part of the D3D matrix
before sending it to RAPID.
Once again, everything else (MAX, RAPID) ... just works.

Pierre


----- Original Message -----
From: <Nik...@ao...>
To: <gda...@li...>
Sent: Thursday, July 27, 2000 8:00 AM
Subject: [Algorithms] OBBs & Max


> Recently, I've been creating an OBB collision detection system for my
engine,
> and I loosely used the RAPID library as a guide when creating my own
> functions.  The data that I use originates from 3D Studio Max 3.1.  I have
> been having much difficulty with the accuracy of the system, so I
attempted
> to use the RAPID library itself to see if that functioned correctly.
> However, the RAPID library is giving the same results as my own, it
> inaccurately reports collision with even the most simple models (such as
two
> boxes, in which only one has rotation).  Is there a problem with the
library,
> or with Max?  The data I am receiving from Max displays correctly when
> rendered with D3D (in the exporter I change the coordinate system from
Max's
> to D3D's).  Could this change in coordinate systems be the problem?  In
this
> transformation, I change the order of the vertices on each face, and I
flip
> rows 2 and 3 in the transformation matrix, along with the y & z
coordinates
> in the matrix and the vertices.   Also, when a box is created in Max, it
is
> defined with the center being at the bottom of the box, and the rotation
and
> translation matrix compensate for this (depending on where the pivot point
is
> located), to make the scene look correct.   (As I mentioned earlier, the
when
> I render this data in D3D, it looks exactly like what it did in Max, in
> addition, the collision detection is accurate if neither model is rotated.
> Any help would be appreciated.
>
> Thanks,
> Nik...@ao...
>
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