gdalgorithms-list

[Algorithms] OBBs & Max

[<Nik...@ao...>]

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...

[Algorithms] OBBs & Max

[<Nik...@ao...>]

I'm resending this message to the list, because oddly it showed up with the 
wrong subject and from the wrong person when reading it with AOL mail (I'm 
not sure if it was just a problem with AOL, or with the list), but I 
apologize for those of you who are receiving this post twice.

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...

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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