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# post-multiply matrices?

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### #1rikun  Members

Posted 24 April 2007 - 05:07 AM

In openGL, what does post-multiplying matrices mean?

### #2Brother Bob  Moderators

Posted 24 April 2007 - 07:04 AM

It means the matrix created by the command called is multiplied with the current matrix from the right. If M is the current matrix and you call, say, glRotate (which creates the matrix R), the new matrix is M*R.

### #3Palidine  Members

Posted 24 April 2007 - 07:19 AM

you distinguish between pre-multiply and post-multiply because matrix multiplication is not commutative (i.e. A*B != B*A).

Explained practically: if you rotate around the global X then the global Y then the global Z you'll get a totally different resultant orientation than if you go Z -> Y -> X.

http://en.wikipedia.org/wiki/Matrix_(mathematics)#Matrix_multiplication

-me

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