mirror of
https://gitlab.gnome.org/GNOME/evince
synced 2024-06-30 22:54:23 +00:00
2ac0d7096f
As the two functions in ev-color-contrast.h might be used elsewhere later in libview. Signed-off-by: Germán Poo-Caamaño <gpoo@gnome.org>
93 lines
3.0 KiB
C
93 lines
3.0 KiB
C
/* ev-color-contrast.c
|
|
* This file is part of Evince, a GNOME document viewer
|
|
*
|
|
* Copyright (C) 2020 Vanadiae <vanadiae35@gmail.com>
|
|
*
|
|
* Evince is free software; you can redistribute it and/or modify it
|
|
* under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation; either version 2 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* Evince is distributed in the hope that it will be useful, but
|
|
* WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
* General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, write to the Free Software
|
|
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
|
|
*/
|
|
|
|
#include <math.h>
|
|
|
|
#include "ev-color-contrast.h"
|
|
|
|
static double
|
|
get_srgb (const double color_component)
|
|
{
|
|
/* calculation of sRGB color is based on note 1 of
|
|
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
|
|
*/
|
|
if (color_component <= 0.03928)
|
|
return color_component / 12.92;
|
|
else
|
|
return powf (((color_component + 0.055) / 1.055), 2.4);
|
|
}
|
|
|
|
static double
|
|
get_relative_luminance (const GdkRGBA *color)
|
|
{
|
|
/* calculation of relative luminance is based on note 1 of
|
|
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
|
|
*/
|
|
return get_srgb (color->red) * 0.2126 + get_srgb (color->blue) * 0.0722 +
|
|
get_srgb (color->green) * 0.7152;
|
|
}
|
|
|
|
static double
|
|
get_contrast_level (const GdkRGBA *bg_color,
|
|
const GdkRGBA *fg_color)
|
|
{
|
|
/* the contrast level calculus is based on WCAG 2.0 guideline 1.4 */
|
|
/* https://www.w3.org/WAI/GL/UNDERSTANDING-WCAG20/visual-audio-contrast7.html#key-terms
|
|
*/
|
|
const double bg_luminance = get_relative_luminance (bg_color);
|
|
const double fg_luminance = get_relative_luminance (fg_color);
|
|
return (fmax (bg_luminance, fg_luminance) + 0.05) / (fmin (bg_luminance, fg_luminance) + 0.05);
|
|
}
|
|
|
|
/**
|
|
* ev_color_get_most_readable_color:
|
|
*
|
|
* Returns: (transfer none): the most readable color on bg_color between
|
|
* first_color and second_color
|
|
*/
|
|
GdkRGBA *
|
|
ev_color_contrast_get_most_readable_color (const GdkRGBA *bg_color,
|
|
GdkRGBA *first_color,
|
|
GdkRGBA *second_color)
|
|
{
|
|
const double first_contrast = get_contrast_level (bg_color, first_color);
|
|
const double second_contrast = get_contrast_level (bg_color, second_color);
|
|
|
|
/* higher is more readable (more contrast) */
|
|
return first_contrast > second_contrast ? first_color : second_color;
|
|
}
|
|
|
|
/**
|
|
* ev_color_get_best_foreground_color:
|
|
*
|
|
* Returns: (transfer full): the most readable foreground color on bg_color
|
|
* between black #000000 and white #FFFFFF
|
|
*/
|
|
GdkRGBA *
|
|
ev_color_contrast_get_best_foreground_color (const GdkRGBA *bg_color)
|
|
{
|
|
GdkRGBA black, white;
|
|
|
|
gdk_rgba_parse (&black, "#000000");
|
|
gdk_rgba_parse (&white, "#FFFFFF");
|
|
|
|
return gdk_rgba_copy (ev_color_contrast_get_most_readable_color (bg_color, &black, &white));
|
|
}
|