bug#12506: 24.2.50; Docview shrinks width to fit screen

[Tassilo Horn <tsdh@gnu.org>]

Ivan Andrus <darthandrus@gmail.com> writes:

> I occasionally use doc-view-mode to read pdfs.  I have noticed that if
> the window is skinnier than the width of the pdf then the width is
> shrunk so that it all fits.  However, the height is not affected.
> This leads to "squished" text which is unreadable.
>
> To see the effect:
>
> 1. emacs -Q
> 2. open a pdf in doc-view-mode
> 3. type "W" for `doc-view-fit-width-to-window'
> 4. C-x 3 to split the window
> 5. You now have a squished picture.
>
> I think it should not scale the width at all (and it did not use to).
> It makes zooming in impossible.  Especially it should not scale the
> width without scaling the height.

I can't reproduce that on a GNU/Linux box.  After step 3, the image fits
exactly the width of the emacs window and the height is set correctly to
keep the aspect ratio.  After step 4, I have two side-by-side windows,
each showing about the left half of the image, but no squishing.

Have you compiled emacs with ImageMagick support?  I guess so, because
else doc-view would fall back to reconversion with any zooming command.
So let's assume you have ImageMagick support, could you please evaluate

  ;; That's basically what doc-view with ImageMagic does when
  ;; fitting/zooming
  (insert-image
   (create-image "/some/image.png"
	         'imagemagick nil :width 100))

and play a bit with the width parameter?  In any case, the image should
keep its original aspect ratio.

,----[ (info "(elisp)ImageMagick Images") ]
| `:width, :height'
|      The `:width' and `:height' keywords are used for scaling the
|      image.  If only one of them is specified, the other one will be
|      calculated so as to preserve the aspect ratio.  If both are
|      specified, aspect ratio may not be preserved.
`----

If you don't have ImageMagick support, could you check if just finding
some png image with image-mode and then splitting has the same squish
effect?

Bye,
Tassilo