Re: [ggt-devel] Re: adding GetColumn to ggt Matrix?

[Eric M. <ema...@um...>]

I'd be happy with either one. I personally prefer the second one since it 
doesn't require the user to create a temporary variable prior to using the 
routine.

Matrix44f lookat_mat = LookAt(gmtl::GetColumn(3,mat),gmtl::GetColumn(1,mat));

as opposed to:

Vec3f a,b;
gmtl::GetColumn(3,mat,a);
gmtl::GetColumn(1,mat,b);
Matrix44f lookat_mat = LookAt(a,b);

Thanks for looking into this!

E.

At 10:39 09/23/2003 -0500, Allen Bierbaum wrote:
>Ben Scott wrote:
>>While it could be considered an unneeded function because you can achieve
>>the same functionality on your own, I have often wanted the ability to get
>>a column from a matrix as vector - especially when getting the forward
>>vector for entities or doing billboarding. It's a relatively simple
>>function that will bloat the API but not the user's code unless they use
>>it. I figure that GMTL is hard enough for most people to grok because of
>>the templates that anything we can do to help them use it and like it is
>>good.
>>I guess if Allen agrees with you and doesn't want it in the library I'll
>>concede and just send Eric the patch rather than commit it.
>>cheers,
>>-Ben
>
>Sounds like a good idea to me.  I would think a GetColumn and a GetRow 
>method would be helpful.
>
>As far as where to put it, we could make it a gmtl method.  Something like:
>
>gmtl::getColumn(unsigned col, Matrix& mat, Vec& vec)
>
>and/or
>
>Vec gmtl::getColumn(unsigned col, Matrix& mat)
>
>What do you guys think?
>
>-Allen
>
>>
>>>
>>>I'm not sure it was an ambiguity, rather it was an effort not to bloat the
>>>code with unneeded functions.
>>>
>>>for example, you can easily write your own GetColumn using the element
>>>accessor operator (  mat[row][col]  ).
>>>
>>>I see it as unneeded, but I'll defer the descision to allen or ben since I
>>>don't feel too strongly about it.
>>>
>>>kevin
>>>
>>>
>>>On Mon, 22 Sep 2003, Eric Maslowski wrote:
>>>
>>>
>>>>Ben said he was going to take a look into adding GetColumn() routine to
>>>>the
>>>>library to simplify this ambiguity. Thanks for the response.
>>>>
>>>>cheers
>>>>
>>>>E.
>>>>
>>>>At 15:13 09/22/2003 -0500, you wrote:
>>>>
>>>>
>>>>>mats are column ordered, so that helps.  you should be able to index
>>>>
>>>>one
>>>>
>>>>>element and dereference it to get the column.
>>>>>
>>>>>I think (float*)&mat.mData[0] would be the first column, which if you
>>>>
>>>>init
>>>>
>>>>>a Vec with it:
>>>>>
>>>>>gmtl::Vec4f col;
>>>>>col.set( (float*)&mat.mData[0] );
>>>>>
>>>>>
>>>>>second column (example):
>>>>>
>>>>>   col.set( (float*)&mat(0,1) );
>>>>>
>>>>>
>>>>>4th column (translation component):
>>>>>
>>>>>   col.set( (float*)&mat[0][3] );
>>>>>
>>>>>
>>>>>
>>>>>-kevin
>>>>>
>>>>>
>>>>>
>>>>>On Mon, 22 Sep 2003, Eric Maslowski wrote:
>>>>>
>>>>>
>>>>>>How this is the right list: What is the recommended method for
>>>>grabbing an
>>>>
>>>>>>entire column?
>>>>>>
>>>>>>Can't seem to find a general GetColumn() routine in the Matrix
>>>>definition.
>>>>
>>>>>>I can't seem to even grab the components and throw them in a vector
>>>>when
>>>>
>>>>>>the Matrix44f is a pointer.
>>>>>>
>>>>>>Matrix44f* mat = entity->GetTransform(); // GetTransform() returns
>>>>>
>>>>>Matrix44f*
>>>>>
>>>>>>Vec3f out_vec(mat[2][0],mat[2][1],mat[2][2]);
>>>>>>
>>>>>>yields:
>>>>>>
>>>>>>error C2664: 'gmtl::Vec<DATA_TYPE,SIZE>::Vec(const DATA_TYPE &,const
>>>>>>DATA_TYPE &,const DATA_TYPE &)' : cannot convert parameter 1 from
>>>>>>'gmtl::Matrix<DATA_TYPE,ROWS,COLS>::RowAccessor *' to 'const float
>>>>&'
>>>>
>>>>>>Any help would be greatly appreciated.
>>>>>>
>>>>>>cheers
>>>>>>
>>>>>>E.
>>>>>>
>>>>>>
>>>>>>
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>>>>>
>>>>>--
>>>>>*--*---*---*----*-----*------*------*-----*----*---*---*--*
>>>>>Kevin Meinert                         /_/
>>>>>home - http://www.vrsource.org/~kevin           \        /
>>>>>music - http://www.subatomicglue.com           \/  __    \/
>>>>>                                                   \__
>>>>>                                            \_\
>>>>
>>>--
>>>*--*---*---*----*-----*------*------*-----*----*---*---*--*
>>>Kevin Meinert                         /_/
>>>home - http://www.vrsource.org/~kevin           \        /
>>>music - http://www.subatomicglue.com           \/  __    \/
>>>                                                   \__
>>>                                            \_\
>>>
>>
>>
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>
>--
>-- Allen Bierbaum                          al...@vr... --
>-- VR Juggler Team                               www.vrjuggler.org --
>-- Virtual Reality Applications Center        www.vrac.iastate.edu --
>
>
>
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