GNU bug report logs - #22343
25.0.50; Incorrect rounding (?) when loading the Emacs.background attribute from Xresources

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Clément Pit--Claudel <clement.pitclaudel <at> live.com>
Cc: 22343 <at> debbugs.gnu.org
Subject: bug#22343: 25.0.50; Incorrect rounding (?) when loading the Emacs.background attribute from Xresources
Date: Mon, 11 Jan 2016 20:56:43 +0200

> From: Clément Pit--Claudel <clement.pitclaudel <at> live.com>
> Date: Sun, 10 Jan 2016 16:19:50 -0500
> 
> This is a cute bug. Run the following two commands (in bash):
> 
> # Set Emacs.background in Xresources
> $ xrdb <(echo "Emacs.background: #2e3436")
> # Run Emacs with same background on default face
> $ emacs -q --eval "(set-face-attribute 'default nil :background \"#2e3436\")"
> 
> On my machine, the two colors are not rendered the same. I've attached a screenshot. What essentially happens is that anywhere where text is drawn the background is indeed #2e3436, but on the rest of the frame it's #2d3335. Amusingly, these two colors have distinct RGB and HSL values, but their CMYK and HSB values are the same (or so says http://rgb.to/hex/2d3335 and http://rgb.to/hex/2e3436, at least).
> 
> The reason I came across this is that I use Emacs' tango-dark theme, which uses that background color. Since I didn't like Emacs popping up with a white background and immediately switching, I set the same background in my .Xresources.
> 
> To observe the bug more clearly, just take a screenshot and open it in your favourite image editor, then use the magic wand with a tolerance of 0 (see other screenshot). Or use the color picker.
> 
> What could cause this problem? A roundtripping issue with color conversions?

Could this be the distant-background feature at work?

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