cairo/src/cairo-color.c

   1 /* cairo - a vector graphics library with display and print output
   2  *
   3  * Copyright © 2002 University of Southern California
   4  * Copyright © 2005 Red Hat, Inc.
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it either under the terms of the GNU Lesser General Public
   8  * License version 2.1 as published by the Free Software Foundation
   9  * (the "LGPL") or, at your option, under the terms of the Mozilla
  10  * Public License Version 1.1 (the "MPL"). If you do not alter this
  11  * notice, a recipient may use your version of this file under either
  12  * the MPL or the LGPL.
  13  *
  14  * You should have received a copy of the LGPL along with this library
  15  * in the file COPYING-LGPL-2.1; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  17  * You should have received a copy of the MPL along with this library
  18  * in the file COPYING-MPL-1.1
  19  *
  20  * The contents of this file are subject to the Mozilla Public License
  21  * Version 1.1 (the "License"); you may not use this file except in
  22  * compliance with the License. You may obtain a copy of the License at
  23  * http://www.mozilla.org/MPL/
  24  *
  25  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
  26  * OF ANY KIND, either express or implied. See the LGPL or the MPL for
  27  * the specific language governing rights and limitations.
  28  *
  29  * The Original Code is the cairo graphics library.
  30  *
  31  * The Initial Developer of the Original Code is University of Southern
  32  * California.
  33  *
  34  * Contributor(s):
  35  *      Carl D. Worth <cworth@cworth.org>
  36  */
  37
  38 #include "cairoint.h"
  39
  40 static cairo_color_t const cairo_color_white = {
  41     1.0,    1.0,    1.0,    1.0,
  42     0xffff, 0xffff, 0xffff, 0xffff
  43 };
  44
  45 static cairo_color_t const cairo_color_black = {
  46     0.0, 0.0, 0.0, 1.0,
  47     0x0, 0x0, 0x0, 0xffff
  48 };
  49
  50 static cairo_color_t const cairo_color_transparent = {
  51     0.0, 0.0, 0.0, 0.0,
  52     0x0, 0x0, 0x0, 0x0
  53 };
  54
  55 static cairo_color_t const cairo_color_magenta = {
  56     1.0,    0.0, 1.0,    1.0,
  57     0xffff, 0x0, 0xffff, 0xffff
  58 };
  59
  60 const cairo_color_t *
  61 _cairo_stock_color (cairo_stock_t stock)
  62 {
  63     switch (stock) {
  64     case CAIRO_STOCK_WHITE:
  65         return &cairo_color_white;
  66     case CAIRO_STOCK_BLACK:
  67         return &cairo_color_black;
  68     case CAIRO_STOCK_TRANSPARENT:
  69         return &cairo_color_transparent;
  70     }
  71
  72     ASSERT_NOT_REACHED;
  73
  74     /* If the user can get here somehow, give a color that indicates a
  75      * problem. */
  76     return &cairo_color_magenta;
  77 }
  78
  79 void
  80 _cairo_color_init (cairo_color_t *color)
  81 {
  82     *color = cairo_color_white;
  83 }
  84
  85 void
  86 _cairo_color_init_rgb (cairo_color_t *color,
  87                        double red, double green, double blue)
  88 {
  89     _cairo_color_init_rgba (color, red, green, blue, 1.0);
  90 }
  91
  92 /* Convert a double in [0.0, 1.0] to an integer in [0, 65535]
  93  * The conversion is designed to divide the input range into 65536
  94  * equally-sized regions. This is achieved by multiplying by 65536 and
  95  * then special-casing the result of an input value of 1.0 so that it
  96  * maps to 65535 instead of 65536.
  97  */
  98 uint16_t
  99 _cairo_color_double_to_short (double d)
 100 {
 101     uint32_t i;
 102     i = (uint32_t) (d * 65536);
 103     i -= (i >> 16);
 104     return i;
 105 }
 106
 107 static void
 108 _cairo_color_compute_shorts (cairo_color_t *color)
 109 {
 110     color->red_short   = _cairo_color_double_to_short (color->red   * color->alpha);
 111     color->green_short = _cairo_color_double_to_short (color->green * color->alpha);
 112     color->blue_short  = _cairo_color_double_to_short (color->blue  * color->alpha);
 113     color->alpha_short = _cairo_color_double_to_short (color->alpha);
 114 }
 115
 116 void
 117 _cairo_color_init_rgba (cairo_color_t *color,
 118                         double red, double green, double blue,
 119                         double alpha)
 120 {
 121     color->red   = red;
 122     color->green = green;
 123     color->blue  = blue;
 124     color->alpha = alpha;
 125
 126     _cairo_color_compute_shorts (color);
 127 }
 128
 129 void
 130 _cairo_color_multiply_alpha (cairo_color_t *color,
 131                              double         alpha)
 132 {
 133     color->alpha *= alpha;
 134
 135     _cairo_color_compute_shorts (color);
 136 }
 137
 138 void
 139 _cairo_color_get_rgba (cairo_color_t *color,
 140                        double        *red,
 141                        double        *green,
 142                        double        *blue,
 143                        double        *alpha)
 144 {
 145     *red   = color->red;
 146     *green = color->green;
 147     *blue  = color->blue;
 148     *alpha = color->alpha;
 149 }
 150
 151 void
 152 _cairo_color_get_rgba_premultiplied (cairo_color_t *color,
 153                                      double        *red,
 154                                      double        *green,
 155                                      double        *blue,
 156                                      double        *alpha)
 157 {
 158     *red   = color->red   * color->alpha;
 159     *green = color->green * color->alpha;
 160     *blue  = color->blue  * color->alpha;
 161     *alpha = color->alpha;
 162 }
 163
 164 cairo_bool_t
 165 _cairo_color_equal (const cairo_color_t *color_a,
 166                     const cairo_color_t *color_b)
 167 {
 168     if (color_a == color_b)
 169         return TRUE;
 170
 171     return color_a->red_short   == color_b->red_short   &&
 172            color_a->green_short == color_b->green_short &&
 173            color_a->blue_short  == color_b->blue_short  &&
 174            color_a->alpha_short == color_b->alpha_short;
 175 }