[ODE] ODE internals: row-major or column-major?
Mauro G. Todeschini
mauro2006todeschini at itia.cnr.it
Fri Oct 6 07:24:21 MST 2006
Mauro G. Todeschini wrote:
> Jon Watte (ODE) wrote:
>> There's also the question of row vectors vs column vectors.
>>
>> See http://www.mindcontrol.org/~hplus/graphics/matrix-layout.html
> Yes, I read that document before asking my question, but It didn't solve
> my doubts.
> I understand that you can use row vectors and post-multiply or column
> vectors and pre-multiply.
> To me It seems that ode pre-multiplies (reading the code from
> dMULTIPLTOP_333 for example) so It should use column vectors on the right:
> A, B, are rotation matrixes and p is a point. B happens (in time) before A.
> p'=ABp is what ode does to obtain the transformed p' point.
> I think that the matrix at the link I posted
> http://planning.cs.uiuc.edu/node102.html
> uses the same convention, so If ode is row-maior and pre-multiplies and
> uses a column vector on the right I still cannot understand why It
> doesn't store the matrix that way dRFromEulerAngles.
Ehm...bad English :D
read: "I cannot understand why It stores the matrix the way It does in
dRFromEulerAngles".
> Ok, I know that It works, and that probably I miss something stupid
> but... I have to understand :D
> I think I need some hints from you experts :D
>
> Bye and Thanks
>
>> Cheers,
>>
>> / h+
>>
>>
>> Mauro G. Todeschini wrote:
>>> Hi,
>>> I'm looking at ode code and I have some question that I haven't been
>>> able to solve googling. So I need your help :)
>>> I've read that ode stores matrixes in memory in row-major style (which
>>> is opposite to OpenGL column major style). I've also read that row-major
>>> means that if I have a (rotation) matrix like this (3 rows, 4 columns):
>>> [m11 m12 m13 m14]
>>> [m21 m22 m23 m24]
>>> [m31 m32 m33 m34]
>>> ... It get stored in an array like this:
>>> [a0]=m11 -
>>> [a1]=m12 First row
>>> [a2]=m13
>>> [a3]=m14 -
>>> [a4]=m21 -
>>> [a5]=m22 Second Row
>>> [a6]=m23
>>> [a7]=m24 -
>>> [a8]=m31 -
>>> [a9]=m32 Third Row
>>> [a10]=m33
>>> [a11]=m34 -
>>> Ok, It seemed clear but... =:-o
>>> I looked at the code of the function dRFromEulerAngles (file
>>> rotation.cpp) and to me It seems that the rotation matrix get stored in
>>> column-major style.
>>> The rotation matrix of the composition of a X rotation followed by a Y
>>> rotation followed by a Z rotation in fact shold have the form shown at
>>> the end of this page:
>>> http://planning.cs.uiuc.edu/node102.html
>>> Anybody can clarify? Is ODE row or column major?
>>> There is something I really cannot catch...
>>>
>>> Thanks and Bye
>>>
>>> _______________________________________________
>>> ODE mailing list
>>> ODE at q12.org
>>> http://q12.org/mailman/listinfo/ode
>>>
>>>
>>>
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