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Re: Image transformations

From: Alan Third
Subject: Re: Image transformations
Date: Wed, 12 Jun 2019 23:15:32 +0100
User-agent: Mutt/1.12.0 (2019-05-25)

On Wed, Jun 12, 2019 at 11:07:46PM +0100, Alan Third wrote:
> > > +   tx and ty represent translations, m11 and m22 represent scaling
> > > +   transforms and m21 and m12 represent shear transforms.

Having written a huge tract and messed around with outputting various
transform matrices, it seems clear to me now that the above is not
quite as straightforward as I was thinking. A 90 degree rotation
followed by a resize doesn’t actually put anything in m11 and m22, so
clearly m11, m12, m21 and m22 interact in mysterious ways.

My feeble excuse is that I’m not a mathematician.
Alan Third

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