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johnnyp05
08-08-2005, 02:31 PM
Hi, can anyone actually point out why, what and where the inverse matrix is used in openGL and why it is useful? thanks! :)

powerpad
08-09-2005, 12:25 AM
you can use the inverse matrix M^-1 of matrix M when you want the changes that M did want to be undone.

If you want another answer then please specify your question

johnnyp05
08-09-2005, 01:17 AM
Ooh right thanks :) What about the determinant of a matrix, how is that useful in 3d graphics/games?

jide
08-10-2005, 02:30 AM
The determinant almost serves for calculating the inverse of a matrix.

Aeluned
08-10-2005, 05:13 AM
It is used to determine whether a polygon is backfacing.

johnnyp05
08-10-2005, 08:20 AM
could you possibly explain how? The thoery behind it? :) If it's too lengthy explanation it doesn't matter :)

Aeluned
08-10-2005, 10:27 AM
The explanation is a bit involved and it requires some knowledge of Linear Algebra.

I won't get into all of that here but I can refer you to this (http://www.cs.berkeley.edu/~ug/slide/pipeline/assignments/backfacecull.shtml)
should you care to read up on it.

memfr0b
08-10-2005, 11:54 PM
The inverse transformation matrix is necessary for vertex normal transformation.

The vertex itself is multiplied with the modelview-projection-matrix. Normals need to be multiplied with the inverse transpose of that matrix to stay correct.