Re: No NEWS entry for doc-view-mupdf-use-svg (Emacs 30.0.91 feedback)

[Tassilo Horn <tsdh@gnu.org>]

Morgan Willcock <morgan@ice9.digital> writes:

>>> I think it is rendering the text and the background of the document
>>> in the same colour.
>>
>> In that case, you may wish to customize the new face
>> doc-view-svg-face.
>
> It seems to be the currently active theme which determines whether the
> the document is readable or not.

The value of the foreground and background doc-view-svg-face properties
are passed as :foreground / :background values to create-image when
inserting the SVG into the buffer.  Their docs are here (info "(elisp)
SVG Images").

--8<---------------cut here---------------start------------->8---
SVG (Scalable Vector Graphics) is an XML format for specifying images.
SVG images support the following additional image descriptor properties:

‘:foreground FOREGROUND’
     FOREGROUND, if non-‘nil’, should be a string specifying a color,
     which is used as the image's foreground color.  If the value is
     ‘nil’, it defaults to the current face's foreground color.

‘:background BACKGROUND’
     BACKGROUND, if non-‘nil’, should be a string specifying a color,
     which is used as the image's background color if the image supports
     transparency.  If the value is ‘nil’, it defaults to the current
     face's background color.
--8<---------------cut here---------------end--------------->8---

Since doc-view-svg-face inherits from the default theme, in theory the
SVG should be adjusted acording to your theme.

> If the SVG rendering is enabled (when available) by default, does this
> mean that it is the user's responsibility to set usable default
> colours?  Or should the theme be setting usable default colours?

The latter.  If the theme sets the default face sensibly (which it
surely does), then your PDFs should look the same.  Well, and that's
true for "normal" PDF documents (black on white, e.g., academic papers)
but somehow fails for "fancy" documents.

I don't know how the :foreground/:background SVG image properties work
but it looks to me as if :background works well every time but
:foreground doesn't as soon as the text is not black.  I suspect the
heuristic is something like: if it's transparent, it's the background,
and if it's either black or white, it's the foreground.

>> What do other applications, like a browser, show for the produced SVG
>> file?  Is it possible that your version of mpdf produces bad SVG
>> images?
>
> I couldn't find any installed utility by that name,

Its mupdf or mudraw.

> but using image-save in the DocView buffer suggests that the actual
> conversion to SVG doesn't have any problems.  It seems to be purely an
> issue with how the SVG image is displayed in the buffer.

You can find the generated SVG files easily using M-x
doc-view-dired-cache RET which opens a dired buffer in the temporary
directory where doc-view stores the files.

Bye,
  Tassilo