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Re: Testing native image scaling
From: |
Eli Zaretskii |
Subject: |
Re: Testing native image scaling |
Date: |
Sun, 20 Jan 2019 18:05:18 +0200 |
> Date: Sat, 19 Jan 2019 21:45:43 +0000
> From: Alan Third <address@hidden>
> Cc: address@hidden
>
> On Sat, Jan 19, 2019 at 11:31:34AM +0200, Eli Zaretskii wrote:
> > Alan, could you please tell how you tested native image scaling with
> > the XRENDER extension, and perhaps show some Lisp or existing commands
> > you used for that? E.g., did the features in thumbs.el work for you
> > in a build without Imagemagick?
>
> I just used a fairly simple series of commands like this:
>
> (setq i (create-image "~/image.png" nil nil :scale 0.5))
> (insert-image i)
> (setq ii (create-image "~/image.png" nil nil :scale 0.5))
> (insert "\n")
> (insert-image ii)
Thanks, this was very helpful. (Actually, just create-image with one
argument is enough: after inserting it, '+' or '-' on the image will
interactively resize it.)
> It look like thumbs.el uses ImageMagick’s convert program directly, so
> it won’t be affected by native scaling.
Ah, okay, I missed that. image-dired seems to do the same. I guess
we should at some point update those (and others) to use the native
resizing.
> > I tried to implement this for MS-Windows, but I guess my understanding
> > of the internal workings of this is incomplete/incorrect, or my code
> > is buggy (or both), because I don't seem to be able to cause Emacs to
> > exercise the code when the original image's size and the size
> > requested by scaling differ. For example, I thought that when scaling
> > is requested, x_set_image_size should be called and compute image
> > dimensions different from the original img->height and img->width, but
> > I seem to be unable to see this. What am I missing? Could you
> > perhaps describe the flow of calls when, e.g., the user types '+' on
> > an image in image-mode, and Emacs scales the image at point?
>
> I think you understand this right.
>
> x_set_image_size calculates the new sizes, does the conversion, and
> writes those new sizes back into struct image, over‐writing the
> original sizes.
>
> For NS it also asks the NSImage back‐end to scale the image using
> ns_image_set_size, which in effect does the actual scaling.
>
> For XRender it sets up an affine transformation matrix, and applies it
> to img->picture, which also in effect does the actual scaling.
>
> The compositing functions in nsterm.m and xterm.c don’t need to know
> the original image size, just the new size, and NSImage/XRender
> handles the rest.
Well, on w32, the implementation actually resizes when it draws.
Maybe that's sub-optimal, but I know next to nothing about w32 image
display, so what I got looks definitely fine for my ignorance.
So we now have native resizing on all major platforms.
> We could use XRender to rotate images if we really wanted to, and the
> NS port already supports it.
Where's the NS support for that? AFAICT, :rotate is only handled in
ImageMagick specific portions of the code, what did I miss?
Thanks.