GNU bug report logs - #15837
24.3; invalid colour conversion from Gtk+3 to X11

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Łukasz Stelmach <stlman <at> poczta.fm>
To: bug-gnu-emacs <at> gnu.org 
Subject: 24.3; invalid colour conversion from Gtk+3 to X11
Date: Fri, 08 Nov 2013 19:16:18 +0100

Hello,

The function[1] that reads foreground and background colours from Gtk+3
(GdkRGBA) and converts them to X11 ones (XColor) uses improper
intermediate representation. The Gtk coulour is formated as
rgbi:<red>/<green>/<blue>. Although values prefixed with rgbi: are meant
to be floating point values like the ones returned by
gtk_style_context_get_*() functions but unlike Gtk colours they are
meant to be linear intensity values and will be gamma corrected[2] using
the tables[3] in Xlib.

You can check the effect for yourself by running:

xterm -bg '#777'
xterm -bg 'rgb:7777/7777/7777'
xterm -bg 'rgb:0.46667/0.46667/0.46667'

The last one will be significantly lighter.

0.46667/0.46667/0.46667 is the value returned by Gtk when a colour is
set to #777.

A patch will follow this report.

References:

[1] http://git.savannah.gnu.org/cgit/emacs.git/tree/src/gtkutil.c?id=c09a36ec78af479cb2ea39bf4bca8743cecd08df#n601

[2] http://cgit.freedesktop.org/xorg/doc/xorg-docs/tree/man/X.man?id=66e800c69fa5348b01e4b9670d6274ba392db7e5#n562

[3] http://cgit.freedesktop.org/xorg/lib/libX11/tree/src/xcms/LRGB.c?id=6cb02b166361200da35ba14f52cd9aaa493eb0ea#n224
-- 
Było mi bardzo miło.                                  --- Rurku. --- ...
>Łukasz<                                --- To dobrze, że mnie słuchasz.

... Droga wśród jabłoni prowadzi w nieznane...

Message #8 received at 15837 <at> debbugs.gnu.org (full text, mbox):

From: Łukasz Stelmach <stlman <at> poczta.fm>
To: 15837 <at> debbugs.gnu.org
Cc: Łukasz Stelmach <stlman <at> poczta.fm>
Subject: [PATCH] Pass colours using rgb: instead of rgbi:
Date: Fri,  8 Nov 2013 19:41:05 +0100

X procedures apply gamma correction to RGBi values which makes colours
obtained from Gtk+ 3.0 and displayed by Emacs look different than in
other Gtk applications.

Signed-off-by: Łukasz Stelmach <stlman <at> poczta.fm>
---
 src/gtkutil.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/gtkutil.c b/src/gtkutil.c
index 7e304d4..b8d8610 100644
--- a/src/gtkutil.c
+++ b/src/gtkutil.c
@@ -596,14 +596,17 @@ xg_check_special_colors (struct frame *f,
     GtkStyleContext *gsty
       = gtk_widget_get_style_context (FRAME_GTK_OUTER_WIDGET (f));
     GdkRGBA col;
-    char buf[sizeof "rgbi://" + 3 * (DBL_MAX_10_EXP + sizeof "-1.000000" - 1)];
+    char buf[sizeof "rgb:rrrr/gggg/bbbb" ];
     int state = GTK_STATE_FLAG_SELECTED|GTK_STATE_FLAG_FOCUSED;
     if (get_fg)
       gtk_style_context_get_color (gsty, state, &col);
     else
       gtk_style_context_get_background_color (gsty, state, &col);
 
-    sprintf (buf, "rgbi:%lf/%lf/%lf", col.red, col.green, col.blue);
+    sprintf (buf, "rgb:%04x/%04x/%04x",
+             (int)(col.red * 65535),
+             (int)(col.green * 65535),
+             (int)(col.blue * 65535));
     success_p = (XParseColor (FRAME_X_DISPLAY (f), FRAME_X_COLORMAP (f),
 			      buf, color)
 		 != 0);
-- 
1.8.1.5

Message #15 received at 15837-done <at> debbugs.gnu.org (full text, mbox):

From: Jan Djärv <jan.h.d <at> swipnet.se>
To: Łukasz Stelmach <stlman <at> poczta.fm>
Cc: 15837-done <at> debbugs.gnu.org
Subject: Re: bug#15837: [PATCH] Pass colours using rgb: instead of rgbi:
Date: Sat, 9 Nov 2013 12:20:57 +0100

Applied, thanks.

	Jan D.

8 nov 2013 kl. 19:41 skrev Łukasz Stelmach <stlman <at> poczta.fm>:

> X procedures apply gamma correction to RGBi values which makes colours
> obtained from Gtk+ 3.0 and displayed by Emacs look different than in
> other Gtk applications.
> 
> Signed-off-by: Łukasz Stelmach <stlman <at> poczta.fm>
> ---
> src/gtkutil.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/src/gtkutil.c b/src/gtkutil.c
> index 7e304d4..b8d8610 100644
> --- a/src/gtkutil.c
> +++ b/src/gtkutil.c
> @@ -596,14 +596,17 @@ xg_check_special_colors (struct frame *f,
>     GtkStyleContext *gsty
>       = gtk_widget_get_style_context (FRAME_GTK_OUTER_WIDGET (f));
>     GdkRGBA col;
> -    char buf[sizeof "rgbi://" + 3 * (DBL_MAX_10_EXP + sizeof "-1.000000" - 1)];
> +    char buf[sizeof "rgb:rrrr/gggg/bbbb" ];
>     int state = GTK_STATE_FLAG_SELECTED|GTK_STATE_FLAG_FOCUSED;
>     if (get_fg)
>       gtk_style_context_get_color (gsty, state, &col);
>     else
>       gtk_style_context_get_background_color (gsty, state, &col);
> 
> -    sprintf (buf, "rgbi:%lf/%lf/%lf", col.red, col.green, col.blue);
> +    sprintf (buf, "rgb:%04x/%04x/%04x",
> +             (int)(col.red * 65535),
> +             (int)(col.green * 65535),
> +             (int)(col.blue * 65535));
>     success_p = (XParseColor (FRAME_X_DISPLAY (f), FRAME_X_COLORMAP (f),
> 			      buf, color)
> 		 != 0);
> -- 
> 1.8.1.5
> 
> 
> 

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