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From: Eli Zaretskii <eliz@gnu.org>
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Subject: Re: Image transformations
Date: Thu, 13 Jun 2019 22:29:27 +0300
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To: Richard Copley <rcopley@gmail.com>
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 (message from Richard Copley on Thu, 13 Jun 2019 20:00:49 +0100)
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> From: Richard Copley <rcopley@gmail.com>
> Date: Thu, 13 Jun 2019 20:00:49 +0100
> Cc: Alp Aker <alptekin.aker@gmail.com>, alan@idiocy.org, 
> 	Emacs Development <emacs-devel@gnu.org>
> 
> XRender uses homogeneous matrices. In this system a 3x3 projective matrix can
> represent any affine transformation as one matrix. The matrix representing a
> translation, then a rotation, then a translation, can then be calculated by
> multiplying three matrices. (It is in fact again a rotation followed by a single
> translation.)

Thanks for a useful and detailed description.