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Clarify the matrix layout 

The columns of the matrix are the images of the standard base vectors rather than the base vectors themselves. Added some 
description of the row-major storage format.
pull/1698/head
Manuel Freiberger 2018-01-09 23:46:36 +01:00 committed by GitHub
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doc/dox.h
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@ -561,17 +561,24 @@ The output UV coordinate system has its origin in the lower-left corner:
@endcode @endcode
Use the #aiProcess_FlipUVs flag to get UV coordinates with the upper-left corner als origin. Use the #aiProcess_FlipUVs flag to get UV coordinates with the upper-left corner als origin.
All matrices in the library are row-major. That means that the matrices are stored row by row in memory, A typical 4x4 matrix including a translational part looks like this:
which is similar to the OpenGL matrix layout. A typical 4x4 matrix including a translational part looks like this:
@code @code
X1 Y1 Z1 T1 X1 Y1 Z1 T1
X2 Y2 Z2 T2 X2 Y2 Z2 T2
X3 Y3 Z3 T3 X3 Y3 Z3 T3
0 0 0 1 0 0 0 1
@endcode @endcode
with (X1, X2, X3) being the X base vector, (Y1, Y2, Y3) being the Y base vector, (Z1, Z2, Z3) with <tt>(X1, X2, X3)</tt> being the image of the X base vector, <tt>(Y1, Y2, Y3)</tt> being the image of the
being the Z base vector and (T1, T2, T3) being the translation part. If you want to use these matrices Y base vector, <tt>(Z1, Z2, Z3)</tt> being the image of the Z base vector and <tt>(T1, T2, T3)</tt> being the
in DirectX functions, you have to transpose them. translation part.
All matrices in the library are row-major. That means that the matrix elements are stored row by row in memory,
which is identical to the OpenGL matrix layout. So the above matrix is stored in memory as
<tt>[X1, Y1, Z1, T1, X2, Y2, Z2, T2, X3, Y3, Z3, T3, 0, 0, 0, 1]</tt>. If you want to use these matrices
in a framework, which expects the matrix layout to be column-major (stored along the columns), such as
DirectX or Matlab, you will have to transpose the matrix first.
To be very precise: The transposition has nothing to do with a left-handed or right-handed coordinate system
but 'converts' between row-major and column-major storage format.
<hr> <hr>