gfx/src/nsColor.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "mozilla/ArrayUtils.h"  // for ArrayLength
   8 #include "mozilla/mozalloc.h"    // for operator delete, etc
   9 #include "mozilla/MathAlgorithms.h"
  10
  11 #include "nsColor.h"
  12 #include <sys/types.h>  // for int32_t
  13 #include "nsDebug.h"    // for NS_ASSERTION, etc
  14 #include "nsStaticNameTable.h"
  15 #include "nsString.h"  // for nsAutoCString, nsString, etc
  16 #include "nscore.h"    // for nsAString, etc
  17 #include "prtypes.h"   // for PR_BEGIN_MACRO, etc
  18
  19 using namespace mozilla;
  20
  21 static int ComponentValue(const char16_t* aColorSpec, int aLen, int color,
  22                           int dpc) {
  23   int component = 0;
  24   int index = (color * dpc);
  25   if (2 < dpc) {
  26     dpc = 2;
  27   }
  28   while (--dpc >= 0) {
  29     char16_t ch = ((index < aLen) ? aColorSpec[index++] : '0');
  30     if (('0' <= ch) && (ch <= '9')) {
  31       component = (component * 16) + (ch - '0');
  32     } else if ((('a' <= ch) && (ch <= 'f')) || (('A' <= ch) && (ch <= 'F'))) {
  33       // "ch&7" handles lower and uppercase hex alphabetics
  34       component = (component * 16) + (ch & 7) + 9;
  35     } else {  // not a hex digit, treat it like 0
  36       component = (component * 16);
  37     }
  38   }
  39   return component;
  40 }
  41
  42 bool NS_HexToRGBA(const nsAString& aColorSpec, nsHexColorType aType,
  43                   nscolor* aResult) {
  44   const char16_t* buffer = aColorSpec.BeginReading();
  45
  46   int nameLen = aColorSpec.Length();
  47   bool hasAlpha = false;
  48   if (nameLen != 3 && nameLen != 6) {
  49     if ((nameLen != 4 && nameLen != 8) || aType == nsHexColorType::NoAlpha) {
  50       // Improperly formatted color value
  51       return false;
  52     }
  53     hasAlpha = true;
  54   }
  55
  56   // Make sure the digits are legal
  57   for (int i = 0; i < nameLen; i++) {
  58     char16_t ch = buffer[i];
  59     if (((ch >= '0') && (ch <= '9')) || ((ch >= 'a') && (ch <= 'f')) ||
  60         ((ch >= 'A') && (ch <= 'F'))) {
  61       // Legal character
  62       continue;
  63     }
  64     // Whoops. Illegal character.
  65     return false;
  66   }
  67
  68   // Convert the ascii to binary
  69   int dpc = ((nameLen <= 4) ? 1 : 2);
  70   // Translate components from hex to binary
  71   int r = ComponentValue(buffer, nameLen, 0, dpc);
  72   int g = ComponentValue(buffer, nameLen, 1, dpc);
  73   int b = ComponentValue(buffer, nameLen, 2, dpc);
  74   int a;
  75   if (hasAlpha) {
  76     a = ComponentValue(buffer, nameLen, 3, dpc);
  77   } else {
  78     a = (dpc == 1) ? 0xf : 0xff;
  79   }
  80   if (dpc == 1) {
  81     // Scale single digit component to an 8 bit value. Replicate the
  82     // single digit to compute the new value.
  83     r = (r << 4) | r;
  84     g = (g << 4) | g;
  85     b = (b << 4) | b;
  86     a = (a << 4) | a;
  87   }
  88   NS_ASSERTION((r >= 0) && (r <= 255), "bad r");
  89   NS_ASSERTION((g >= 0) && (g <= 255), "bad g");
  90   NS_ASSERTION((b >= 0) && (b <= 255), "bad b");
  91   NS_ASSERTION((a >= 0) && (a <= 255), "bad a");
  92   *aResult = NS_RGBA(r, g, b, a);
  93   return true;
  94 }
  95
  96 // This implements part of the algorithm for legacy behavior described in
  97 // http://www.whatwg.org/specs/web-apps/current-work/complete/common-microsyntaxes.html#rules-for-parsing-a-legacy-color-value
  98 bool NS_LooseHexToRGB(const nsString& aColorSpec, nscolor* aResult) {
  99   if (aColorSpec.EqualsLiteral("transparent")) {
 100     return false;
 101   }
 102
 103   int nameLen = aColorSpec.Length();
 104   const char16_t* colorSpec = aColorSpec.get();
 105   if (nameLen > 128) {
 106     nameLen = 128;
 107   }
 108
 109   if ('#' == colorSpec[0]) {
 110     ++colorSpec;
 111     --nameLen;
 112   }
 113
 114   // digits per component
 115   int dpc = (nameLen + 2) / 3;
 116   int newdpc = dpc;
 117
 118   // Use only the rightmost 8 characters of each component.
 119   if (newdpc > 8) {
 120     nameLen -= newdpc - 8;
 121     colorSpec += newdpc - 8;
 122     newdpc = 8;
 123   }
 124
 125   // And then keep trimming characters at the left until we'd trim one
 126   // that would leave a nonzero value, but not past 2 characters per
 127   // component.
 128   while (newdpc > 2) {
 129     bool haveNonzero = false;
 130     for (int c = 0; c < 3; ++c) {
 131       MOZ_ASSERT(c * dpc < nameLen,
 132                  "should not pass end of string while newdpc > 2");
 133       char16_t ch = colorSpec[c * dpc];
 134       if (('1' <= ch && ch <= '9') || ('A' <= ch && ch <= 'F') ||
 135           ('a' <= ch && ch <= 'f')) {
 136         haveNonzero = true;
 137         break;
 138       }
 139     }
 140     if (haveNonzero) {
 141       break;
 142     }
 143     --newdpc;
 144     --nameLen;
 145     ++colorSpec;
 146   }
 147
 148   // Translate components from hex to binary
 149   int r = ComponentValue(colorSpec, nameLen, 0, dpc);
 150   int g = ComponentValue(colorSpec, nameLen, 1, dpc);
 151   int b = ComponentValue(colorSpec, nameLen, 2, dpc);
 152   NS_ASSERTION((r >= 0) && (r <= 255), "bad r");
 153   NS_ASSERTION((g >= 0) && (g <= 255), "bad g");
 154   NS_ASSERTION((b >= 0) && (b <= 255), "bad b");
 155
 156   *aResult = NS_RGB(r, g, b);
 157   return true;
 158 }
 159
 160 // Fast approximate division by 255. It has the property that
 161 // for all 0 <= n <= 255*255, FAST_DIVIDE_BY_255(n) == n/255.
 162 // But it only uses two adds and two shifts instead of an
 163 // integer division (which is expensive on many processors).
 164 //
 165 // equivalent to target=v/255
 166 #define FAST_DIVIDE_BY_255(target, v)        \
 167   PR_BEGIN_MACRO                             \
 168   unsigned tmp_ = v;                         \
 169   target = ((tmp_ << 8) + tmp_ + 255) >> 16; \
 170   PR_END_MACRO
 171
 172 // Macro to blend two colors
 173 //
 174 // equivalent to target = (bg*(255-fgalpha) + fg*fgalpha)/255
 175 #define MOZ_BLEND(target, bg, fg, fgalpha) \
 176   FAST_DIVIDE_BY_255(target, (bg) * (255 - fgalpha) + (fg) * (fgalpha))
 177
 178 nscolor NS_ComposeColors(nscolor aBG, nscolor aFG) {
 179   // This function uses colors that are non premultiplied alpha.
 180   int r, g, b, a;
 181
 182   int bgAlpha = NS_GET_A(aBG);
 183   int fgAlpha = NS_GET_A(aFG);
 184
 185   // Compute the final alpha of the blended color
 186   // a = fgAlpha + bgAlpha*(255 - fgAlpha)/255;
 187   FAST_DIVIDE_BY_255(a, bgAlpha * (255 - fgAlpha));
 188   a = fgAlpha + a;
 189   int blendAlpha;
 190   if (a == 0) {
 191     // In this case the blended color is totally trasparent,
 192     // we preserve the color information of the foreground color.
 193     blendAlpha = 255;
 194   } else {
 195     blendAlpha = (fgAlpha * 255) / a;
 196   }
 197   MOZ_BLEND(r, NS_GET_R(aBG), NS_GET_R(aFG), blendAlpha);
 198   MOZ_BLEND(g, NS_GET_G(aBG), NS_GET_G(aFG), blendAlpha);
 199   MOZ_BLEND(b, NS_GET_B(aBG), NS_GET_B(aFG), blendAlpha);
 200
 201   return NS_RGBA(r, g, b, a);
 202 }