Re: Native image rotation

[Alan Third <alan@idiocy.org>]

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