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libview: make contrast functions available in all libview/
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>
This commit is contained in:
vanadiae
Germán Poo-Caamaño
parent
4e49798df1
commit
2ac0d7096f
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@ -25,6 +25,7 @@
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#include <math.h>
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#include "ev-annotation-window.h"
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#include "ev-color-contrast.h"
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#include "ev-stock-icons.h"
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#include "ev-view-marshal.h"
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#include "ev-document-misc.h"
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@ -119,64 +120,6 @@ ev_annotation_window_sync_contents (EvAnnotationWindow *window)
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g_free (contents);
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}
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static double
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get_srgb (const double color_component)
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{
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/* calculation of sRGB color is based on note 1 of https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef */
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if (color_component <= 0.03928)
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return color_component / 12.92;
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else
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return powf (((color_component + 0.055) / 1.055), 2.4);
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}
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static double
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get_relative_luminance (const GdkRGBA *color)
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{
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/* calculation of relative luminance is based on note 1 of https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef */
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return get_srgb (color->red) * 0.2126 + get_srgb (color->blue) * 0.0722 + get_srgb (color->green) * 0.7152;
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}
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static double
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get_contrast_level (const GdkRGBA *bg_color,
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const GdkRGBA *fg_color)
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{
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/* the contrast level calculus is based on WCAG 2.0 guideline 1.4 */
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/* https://www.w3.org/WAI/GL/UNDERSTANDING-WCAG20/visual-audio-contrast7.html#key-terms */
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const double bg_luminance = get_relative_luminance (bg_color);
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const double fg_luminance = get_relative_luminance (fg_color);
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return (fmax (bg_luminance, fg_luminance) + 0.05) / (fmin (bg_luminance, fg_luminance) + 0.05);
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}
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/**
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* get_most_readable_color:
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*
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* Returns: (transfer none): the most readable color on bg_color between first_color and second_color
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*/
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static GdkRGBA *
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get_most_readable_color (const GdkRGBA *bg_color,
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GdkRGBA *first_color,
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GdkRGBA *second_color)
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{
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const double first_contrast = get_contrast_level (bg_color, first_color);
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const double second_contrast = get_contrast_level (bg_color, second_color);
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/* higher is more readable (more contrast) */
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return first_contrast > second_contrast ? first_color : second_color;
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}
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/**
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* get_best_foreground_color:
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*
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* Returns: (transfer full): the most readable foreground color on bg_color between black #000000 and white #FFFFFF
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*/
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static GdkRGBA *
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get_best_foreground_color (const GdkRGBA *bg_color)
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{
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GdkRGBA black, white;
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gdk_rgba_parse (&black, "#000000");
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gdk_rgba_parse (&white, "#FFFFFF");
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return gdk_rgba_copy (get_most_readable_color (bg_color, &black, &white));
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}
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static void
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ev_annotation_window_set_color (EvAnnotationWindow *window,
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GdkRGBA *color)
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@ -185,7 +128,7 @@ ev_annotation_window_set_color (EvAnnotationWindow *window,
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g_autofree char *rgba_str = gdk_rgba_to_string (color);
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g_autofree char *css_data = NULL;
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g_autoptr (GError) error = NULL;
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g_autoptr (GdkRGBA) icon_color = get_best_foreground_color (color);
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g_autoptr (GdkRGBA) icon_color = ev_color_contrast_get_best_foreground_color (color);
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g_autofree char *icon_color_str = gdk_rgba_to_string (icon_color);
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css_data = g_strdup_printf ("button {border-color: %1$s; color: %2$s; -gtk-icon-shadow:0 0; box-shadow:0 0;}\n\
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button:hover {background: lighter(%1$s); border-color: darker(%1$s);}\n\
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92
libview/ev-color-contrast.c
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92
libview/ev-color-contrast.c
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@ -0,0 +1,92 @@
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/* ev-color-contrast.c
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* This file is part of Evince, a GNOME document viewer
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*
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* Copyright (C) 2020 Vanadiae <vanadiae35@gmail.com>
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*
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* Evince is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* Evince is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include <math.h>
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#include "ev-color-contrast.h"
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static double
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get_srgb (const double color_component)
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{
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/* calculation of sRGB color is based on note 1 of
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* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
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*/
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if (color_component <= 0.03928)
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return color_component / 12.92;
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else
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return powf (((color_component + 0.055) / 1.055), 2.4);
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}
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static double
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get_relative_luminance (const GdkRGBA *color)
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{
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/* calculation of relative luminance is based on note 1 of
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* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
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*/
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return get_srgb (color->red) * 0.2126 + get_srgb (color->blue) * 0.0722 +
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get_srgb (color->green) * 0.7152;
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}
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static double
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get_contrast_level (const GdkRGBA *bg_color,
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const GdkRGBA *fg_color)
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{
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/* the contrast level calculus is based on WCAG 2.0 guideline 1.4 */
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/* https://www.w3.org/WAI/GL/UNDERSTANDING-WCAG20/visual-audio-contrast7.html#key-terms
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*/
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const double bg_luminance = get_relative_luminance (bg_color);
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const double fg_luminance = get_relative_luminance (fg_color);
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return (fmax (bg_luminance, fg_luminance) + 0.05) / (fmin (bg_luminance, fg_luminance) + 0.05);
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}
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/**
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* ev_color_get_most_readable_color:
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*
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* Returns: (transfer none): the most readable color on bg_color between
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* first_color and second_color
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*/
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GdkRGBA *
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ev_color_contrast_get_most_readable_color (const GdkRGBA *bg_color,
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GdkRGBA *first_color,
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GdkRGBA *second_color)
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{
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const double first_contrast = get_contrast_level (bg_color, first_color);
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const double second_contrast = get_contrast_level (bg_color, second_color);
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/* higher is more readable (more contrast) */
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return first_contrast > second_contrast ? first_color : second_color;
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}
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/**
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* ev_color_get_best_foreground_color:
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*
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* Returns: (transfer full): the most readable foreground color on bg_color
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* between black #000000 and white #FFFFFF
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*/
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GdkRGBA *
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ev_color_contrast_get_best_foreground_color (const GdkRGBA *bg_color)
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{
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GdkRGBA black, white;
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gdk_rgba_parse (&black, "#000000");
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gdk_rgba_parse (&white, "#FFFFFF");
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return gdk_rgba_copy (ev_color_contrast_get_most_readable_color (bg_color, &black, &white));
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}
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36
libview/ev-color-contrast.h
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36
libview/ev-color-contrast.h
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@ -0,0 +1,36 @@
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/* ev-color-contrast.h
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* this file is part of evince, a gnome document viewer
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*
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* Copyright (C) 2020 Vanadiae <vanadiae35@gmail.com>
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*
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* Evince is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* Evince is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#if !defined (EVINCE_COMPILATION)
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#error "This is a private header."
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#endif
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#ifndef __EV_COLOR_CONTRAST_H__
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#define __EV_COLOR_CONTRAST_H__
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#include <gdk/gdk.h>
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GdkRGBA *ev_color_contrast_get_most_readable_color (const GdkRGBA *bg_color,
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GdkRGBA *first_color,
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GdkRGBA *second_color);
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GdkRGBA *ev_color_contrast_get_best_foreground_color (const GdkRGBA *bg_color);
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#endif /* __EV_COLOR_CONTRAST_H__ */
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@ -19,6 +19,7 @@ install_headers(
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sources = files(
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'ev-annotation-window.c',
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'ev-color-contrast.c',
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'ev-document-model.c',
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'ev-form-field-accessible.c',
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'ev-image-accessible.c',
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