GNU bug report logs - #36315
27.0.50; SVG transparency handling is inaccurate

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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#36315: closed (27.0.50; SVG transparency handling is inaccurate)
Date: Fri, 18 Dec 2020 18:05:02 +0000

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Your message dated Fri, 18 Dec 2020 18:04:45 +0000
with message-id <X9zvPV5PFsb7DM74 <at> breton.holly.idiocy.org>
and subject line Re: bug#36315: Incorrect SVG color
has caused the debbugs.gnu.org bug report #36315,
regarding 27.0.50; SVG transparency handling is inaccurate
to be marked as done.

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


-- 
36315: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=36315
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Pip Cet <pipcet <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.0.50; SVG transparency handling is inaccurate
Date: Thu, 20 Jun 2019 20:26:53 +0000

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Evaluate the following in emacs -Q:

(require 'svg)

(defun make-image (color)
  (let ((svg (svg-create 100 100)))
    (svg-rectangle svg 0 0 100 100 :fill color)
    (svg-image svg)))

(set-frame-parameter (window-frame) 'background-color "black")

(insert (propertize " " 'display (make-image "#f00000")))

The expected result is a rectangle (on black background) of color
#f00000. The actual result is a rectangle of color #ef0000. For black
backgrounds, white is no longer representable.

This is related to bug #36304, but much easier to fix.

Patch attached.

[0001-SVG-scale-color-values-properly.patch (text/x-patch, attachment)]

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From: Alan Third <alan <at> idiocy.org>
To: Qiantan Hong <qhong <at> mit.edu>
Cc: "36315 <at> debbugs.gnu.org" <36315-done <at> debbugs.gnu.org>
Subject: Re: bug#36315: Incorrect SVG color
Date: Fri, 18 Dec 2020 18:04:45 +0000

On Fri, Dec 18, 2020 at 04:42:03PM +0000, Qiantan Hong wrote:
> I fixed my build and it behaves correctly on macOS
> now.
> 
> M-x emacs-version
> GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin18.7.0, NS appkit-1671.60 Version 10.14.6 (Build 18G6032)) of 2020-12-18

Excellent! Thanks for letting us know.

> To make sure I understand it, did we start outsourcing color some point after 27.1?

We pass the foreground and background colours into librsvg, which
creates the bitmap image that's displayed, in a commit that's just a
few months old. It will appear in Emacs 28.

I don't expect the change to be included in Emacs 27 since it's a
fairly large change introducing a number of new features and any new
Emacs 27 releases will be primarily bug fixes.
-- 
Alan Third

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