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Re: Native image rotation

From: Alan Third
Subject: Re: Native image rotation
Date: Sun, 24 Feb 2019 23:22:28 +0000
User-agent: Mutt/1.11.2 (2019-01-07)

On Sun, Feb 24, 2019 at 06:14:30PM +0200, Eli Zaretskii wrote:
> Though I wonder what would be the use cases for rotating images in
> Emacs by angles other than integral multiples of 90 deg.

I’ve no idea, but the maths required isn’t significantly easier as we
still need to calculate the two transforms and the rotation. The main
advantage would be that we could replace all sin(r) and cos(r)
instances with either 1 or 0, but I expect we would get a better
performance improvement from precalculating those values and the
matrix multiplications.

And I guess we maybe wouldn’t have to worry about clearing under the
image any more in X: rotating can leave transparent sections.

But the maths is performed only once, when the image is loaded, so I
doubt we’d find a significant improvement.

Alan Third

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