GNU bug report logs - #40845
SVG rendering issues

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Alan Third <alan <at> idiocy.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#40845: closed (SVG rendering issues)
Date: Sun, 23 Aug 2020 15:30:02 +0000

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Your message dated Sun, 23 Aug 2020 17:29:44 +0200 (CEST)
with message-id <20200823152941.GI89421 <at> breton.holly.idiocy.org>
and subject line Re: bug#40845: SVG rendering issues
has caused the debbugs.gnu.org bug report #40845,
regarding SVG rendering issues
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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From: Clément Pit-Claudel <cpitclaudel <at> gmail.com>
To: bug-gnu-emacs <bug-gnu-emacs <at> gnu.org>
Subject: SVG rendering issues
Date: Sat, 25 Apr 2020 08:19:01 -0400

Hi all,

As discussed on the mailing list, a number of issues currently exist with our SVG rendering implementation.  I have tried to summarize the ones I'm aware of in the following example.

(with-current-buffer (get-buffer-create "*svg bugs*")
  (erase-buffer)
  (require 'face-remap)
  (setq text-scale-mode-amount 10)
  (text-scale-mode)
  (let ((svg (svg-create 16 16)))
    (svg-ellipse svg 8 8 4 4)
    (insert "Text: ")
    (print (svg-image svg :ascent 100))
    (insert-image (svg-image svg :ascent 100))
    (insert-image (svg-image svg :scale 5.0 :ascent 'center :foreground "red" :background "darkgreen"))
    (add-text-properties
     (point-min) (point-max)
     '(face (:foreground "orange" :background "purple")
            mouse-face '(:foreground "purple" :background "orange"))))
  (pop-to-buffer (current-buffer)))

The issues:

1. Manually scaling an image, as is done for the second image, doesn't re-render the svg: is scales the bitmap-rendered version of it, causing blurriness.
2. The SVG images don't inherit the background of the current face; instead, they inherit the background of the default face.
3. The SVG images don't inherit the foreground of the current face; instead, they use a black foreground.
4. The :foreground keyword has no effect on svg images.
5. The images are not scaled with the text: changing text-scale-mode-amount doesn't change the size of the images.

For 1, 2, 3, and 4, the expected behavior is easy to define:
- For 1, the image should be scaled before being rasterized. 
- For 2 and 3, the image should inherit the characteristics of the current face, and be re-rendered if that face changes (e.g. when mouse-face applies, which is important for buttons)
- For 4, the :foreground property should be respected

For 5, it's a bit trickier.  One option would be to accept a float-valued :height specification and treat that as a multiple of the current font size.

A partial workaround for 2 is to add an explicit :background, but it doesn't help with face changes, such as applying a mouse-face.  For 1 and 5 it can be enough to set the size in the SVG and add hooks, but that only works easily for SVGs created within emacs.  For 3 and 4, I don't know of a workaround except modifying the SVG.

Cheers,
Clément.

[Message part 3 (message/rfc822, inline)]

From: Alan Third <alan <at> idiocy.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: cpitclaudel <at> gmail.com, 40845-done <at> debbugs.gnu.org, pipcet <at> gmail.com
Subject: Re: bug#40845: SVG rendering issues
Date: Sun, 23 Aug 2020 17:29:44 +0200 (CEST)

On Sun, Aug 23, 2020 at 03:23:33PM +0300, Eli Zaretskii wrote:
> > Date: Sun, 23 Aug 2020 14:19:28 +0200 (CEST)
> > From: Alan Third <alan <at> idiocy.org>
> > Cc: cpitclaudel <at> gmail.com, 40845 <at> debbugs.gnu.org, pipcet <at> gmail.com
> > 
> > *** The background and foreground of images now default to face
> > colors.  When an image doesn't specify a foreground or background
> > color, Emacs now uses colors from the face used to draw the
> > surrounding text instead of the frame's default colors.
> > 
> > To load images with the default frame colors use the ':foreground'
> > and ':background' image attributes, for example:
> > 
> >     (create-image "filename" nil nil
> >                   :foreground (face-attribute 'default :foreground)
> >                   :background (face-attribute 'default :background))
> > 
> > This change doesn't affect image types that do not support foreground
> > and background colors, such as png or jpeg.
> 
> Almost perfect: I would suggest to modify the last sentence so that it
> tells which types of images do support this feature.

Thanks. I've pushed it to master.
-- 
Alan Third

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