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Re: Native image rotation

From: Daniel Pittman
Subject: Re: Native image rotation
Date: Tue, 26 Feb 2019 12:01:24 -0500

As others, I'd certainly like to be able to perform arbitrary rotations.  Working with photos to extract, eg, document contents from a scanned image, and displaying a graphical "busy" spinner, are the use cases I have handled before.

If performance was too poor, I'd be more inclined to look at how to improve performance in Emacs than to abandon the approach in favor of a large number of barely changed images.  That would, after all, make life better for everyone, and I have confidence that it *would* be possible to make that efficient enough to work.

After all, I don't need 60FPS rendering of this, and that is definitely achievable for vastly more complex 2D and 3D layouts on the display layers on all the platforms Emacs supports, thanks to browsers among other tools.

On Mon, Feb 25, 2019 at 2:21 PM Alan Third <address@hidden> wrote:
On Mon, Feb 25, 2019 at 05:36:46AM +0200, Eli Zaretskii wrote:
> > Date: Sun, 24 Feb 2019 23:22:28 +0000
> > From: Alan Third <address@hidden>
> > Cc: address@hidden
> >
> > 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.
> It's indeed the clearing that bothered me,

Would it be better if it was done by another XRender composite rather
than x_clear_area?

If this really is a problem then I think we have to allow only 90
degree multiples. I can’t see any other reasonable solution.

> and also the increase in the screen estate taken by a rotated image.

I think that would be less of an issue with the addition of cropping,
as an image could be rotated then cropped down to size. Besides, if
someone wants to rotate at 45 degrees they’ve got to expect the size
of the image to change, there’s no other reasonable option.

> I'm asking whether it's worth it.

Limiting to 90 degree increments feels like an arbitrary limitation,
but I don’t feel strongly about it either way.
Alan Third

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