Re: Native image rotation

[Daniel Pittman <slippycheeze@google.com>]

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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 <alan@idiocy.org> 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 <alan@idiocy.org>
> > > Cc: emacs-devel@gnu.org
> > >
> > > 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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