Inverse Matrix

[johnnyp05]

Hi, can anyone actually point out why, what and where the inverse matrix is used in openGL and why it is useful? thanks! :)

[powerpad]

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]

Ooh right thanks :) What about the determinant of a matrix, how is that useful in 3d graphics/games?

[jide]

The determinant almost serves for calculating the inverse of a matrix.

[Aeluned]

It is used to determine whether a polygon is backfacing.

[johnnyp05]

could you possibly explain how? The thoery behind it? :) If it's too lengthy explanation it doesn't matter :)

[Aeluned]

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]

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.