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1 <HTML
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2 ><HEAD
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3 ><TITLE
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4 >SDL_PixelFormat</TITLE
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5 ><META
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6 NAME="GENERATOR"
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7 CONTENT="Modular DocBook HTML Stylesheet Version 1.61
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8 "><LINK
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9 REL="HOME"
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10 TITLE="SDL Library Documentation"
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11 HREF="index.html"><LINK
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12 REL="UP"
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13 TITLE="Video"
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14 HREF="video.html"><LINK
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15 REL="PREVIOUS"
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16 TITLE="SDL_Palette"
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17 HREF="sdlpalette.html"><LINK
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18 REL="NEXT"
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19 TITLE="SDL_Surface"
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20 HREF="sdlsurface.html"></HEAD
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21 ><BODY
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22 CLASS="REFENTRY"
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23 BGCOLOR="#FFF8DC"
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26 VLINK="#551a8b"
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27 ALINK="#ff0000"
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28 ><DIV
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29 CLASS="NAVHEADER"
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30 ><TABLE
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31 WIDTH="100%"
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32 BORDER="0"
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33 CELLPADDING="0"
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34 CELLSPACING="0"
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35 ><TR
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36 ><TH
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37 COLSPAN="3"
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38 ALIGN="center"
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39 >SDL Library Documentation</TH
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40 ></TR
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41 ><TR
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42 ><TD
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43 WIDTH="10%"
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44 ALIGN="left"
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45 VALIGN="bottom"
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46 ><A
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47 HREF="sdlpalette.html"
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48 >Prev</A
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49 ></TD
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50 ><TD
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51 WIDTH="80%"
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52 ALIGN="center"
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53 VALIGN="bottom"
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54 ></TD
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55 ><TD
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56 WIDTH="10%"
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57 ALIGN="right"
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58 VALIGN="bottom"
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59 ><A
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60 HREF="sdlsurface.html"
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61 >Next</A
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62 ></TD
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63 ></TR
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64 ></TABLE
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65 ><HR
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66 ALIGN="LEFT"
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67 WIDTH="100%"></DIV
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68 ><H1
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69 ><A
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70 NAME="SDLPIXELFORMAT"
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71 >SDL_PixelFormat</A
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72 ></H1
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73 ><DIV
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74 CLASS="REFNAMEDIV"
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75 ><A
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76 NAME="AEN2677"
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77 ></A
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78 ><H2
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79 >Name</H2
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80 >SDL_PixelFormat -- Stores surface format information</DIV
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81 ><DIV
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82 CLASS="REFSECT1"
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83 ><A
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84 NAME="AEN2680"
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85 ></A
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86 ><H2
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87 >Structure Definition</H2
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88 ><PRE
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89 CLASS="PROGRAMLISTING"
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90 >typedef struct{
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91 SDL_Palette *palette;
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92 Uint8 BitsPerPixel;
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93 Uint8 BytesPerPixel;
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94 Uint32 Rmask, Gmask, Bmask, Amask;
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95 Uint8 Rshift, Gshift, Bshift, Ashift;
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96 Uint8 Rloss, Gloss, Bloss, Aloss;
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97 Uint32 colorkey;
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98 Uint8 alpha;
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99 } SDL_PixelFormat;</PRE
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100 ></DIV
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101 ><DIV
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102 CLASS="REFSECT1"
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103 ><A
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104 NAME="AEN2683"
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105 ></A
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106 ><H2
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107 >Structure Data</H2
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108 ><DIV
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109 CLASS="INFORMALTABLE"
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110 ><A
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111 NAME="AEN2685"
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112 ></A
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113 ><P
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114 ></P
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115 ><TABLE
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116 BORDER="0"
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117 CLASS="CALSTABLE"
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118 ><TBODY
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119 ><TR
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120 ><TD
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121 ALIGN="LEFT"
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122 VALIGN="TOP"
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123 ><TT
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124 CLASS="STRUCTFIELD"
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125 ><I
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126 >palette</I
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127 ></TT
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128 ></TD
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129 ><TD
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130 ALIGN="LEFT"
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131 VALIGN="TOP"
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132 >Pointer to the <A
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133 HREF="sdlpalette.html"
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134 >palette</A
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135 >, or <TT
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136 CLASS="LITERAL"
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137 >NULL</TT
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138 > if the <TT
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139 CLASS="STRUCTFIELD"
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140 ><I
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141 >BitsPerPixel</I
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142 ></TT
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143 >>8</TD
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144 ></TR
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145 ><TR
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146 ><TD
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147 ALIGN="LEFT"
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148 VALIGN="TOP"
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149 ><TT
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150 CLASS="STRUCTFIELD"
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151 ><I
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152 >BitsPerPixel</I
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153 ></TT
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154 ></TD
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155 ><TD
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156 ALIGN="LEFT"
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157 VALIGN="TOP"
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158 >The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32.</TD
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159 ></TR
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160 ><TR
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161 ><TD
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162 ALIGN="LEFT"
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163 VALIGN="TOP"
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164 ><TT
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165 CLASS="STRUCTFIELD"
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166 ><I
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167 >BytesPerPixel</I
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168 ></TT
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169 ></TD
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170 ><TD
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171 ALIGN="LEFT"
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172 VALIGN="TOP"
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173 >The number of bytes used to represent each pixel in a surface. Usually one to four.</TD
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174 ></TR
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175 ><TR
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176 ><TD
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177 ALIGN="LEFT"
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178 VALIGN="TOP"
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179 ><TT
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180 CLASS="STRUCTFIELD"
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181 ><I
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182 >[RGBA]mask</I
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183 ></TT
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184 ></TD
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185 ><TD
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186 ALIGN="LEFT"
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187 VALIGN="TOP"
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188 >Binary mask used to retrieve individual color values</TD
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189 ></TR
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190 ><TR
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191 ><TD
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192 ALIGN="LEFT"
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193 VALIGN="TOP"
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194 ><TT
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195 CLASS="STRUCTFIELD"
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196 ><I
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197 >[RGBA]loss</I
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198 ></TT
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199 ></TD
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200 ><TD
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201 ALIGN="LEFT"
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202 VALIGN="TOP"
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203 >Precision loss of each color component (2<SUP
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204 >[RGBA]loss</SUP
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205 >)</TD
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206 ></TR
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207 ><TR
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208 ><TD
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209 ALIGN="LEFT"
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210 VALIGN="TOP"
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211 ><TT
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212 CLASS="STRUCTFIELD"
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213 ><I
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214 >[RGBA]shift</I
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215 ></TT
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216 ></TD
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217 ><TD
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218 ALIGN="LEFT"
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219 VALIGN="TOP"
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220 >Binary left shift of each color component in the pixel value</TD
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221 ></TR
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222 ><TR
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223 ><TD
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224 ALIGN="LEFT"
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225 VALIGN="TOP"
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226 ><TT
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227 CLASS="STRUCTFIELD"
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228 ><I
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229 >colorkey</I
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230 ></TT
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231 ></TD
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232 ><TD
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233 ALIGN="LEFT"
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234 VALIGN="TOP"
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235 >Pixel value of transparent pixels</TD
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236 ></TR
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237 ><TR
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238 ><TD
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239 ALIGN="LEFT"
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240 VALIGN="TOP"
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241 ><TT
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242 CLASS="STRUCTFIELD"
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243 ><I
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244 >alpha</I
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245 ></TT
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246 ></TD
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247 ><TD
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248 ALIGN="LEFT"
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249 VALIGN="TOP"
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250 >Overall surface alpha value</TD
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251 ></TR
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252 ></TBODY
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253 ></TABLE
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254 ><P
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255 ></P
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256 ></DIV
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257 ></DIV
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258 ><DIV
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259 CLASS="REFSECT1"
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260 ><A
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261 NAME="AEN2724"
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262 ></A
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263 ><H2
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264 >Description</H2
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265 ><P
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266 >A <SPAN
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267 CLASS="STRUCTNAME"
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268 >SDL_PixelFormat</SPAN
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269 > describes the format of the pixel data stored at the <TT
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270 CLASS="STRUCTFIELD"
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271 ><I
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272 >pixels</I
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273 ></TT
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274 > field of a <A
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275 HREF="sdlsurface.html"
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276 ><SPAN
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277 CLASS="STRUCTNAME"
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278 >SDL_Surface</SPAN
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279 ></A
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280 >. Every surface stores a <SPAN
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281 CLASS="STRUCTNAME"
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282 >SDL_PixelFormat</SPAN
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283 > in the <TT
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284 CLASS="STRUCTFIELD"
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285 ><I
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286 >format</I
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287 ></TT
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288 > field.</P
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289 ><P
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290 >If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential.</P
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291 ><P
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292 >8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 <TT
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293 CLASS="STRUCTFIELD"
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294 ><I
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295 >BitsPerPixel</I
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296 ></TT
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297 > and 1 <TT
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298 CLASS="STRUCTFIELD"
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299 ><I
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300 >BytesPerPixel</I
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301 ></TT
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302 >. Since <TT
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303 CLASS="STRUCTFIELD"
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304 ><I
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305 >BytesPerPixel</I
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306 ></TT
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307 > is 1, all pixels are represented by a Uint8 which contains an index into <TT
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308 CLASS="STRUCTFIELD"
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309 ><I
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310 >palette</I
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311 ></TT
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312 >-><TT
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313 CLASS="STRUCTFIELD"
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314 ><I
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315 >colors</I
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316 ></TT
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317 >. So, to determine the color of a pixel in a 8-bit surface: we read the color index from <SPAN
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318 CLASS="STRUCTNAME"
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319 >surface</SPAN
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320 >-><TT
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321 CLASS="STRUCTFIELD"
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322 ><I
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323 >pixels</I
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324 ></TT
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325 > and we use that index to read the <A
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326 HREF="sdlcolor.html"
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327 ><SPAN
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328 CLASS="STRUCTNAME"
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329 >SDL_Color</SPAN
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330 ></A
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331 > structure from <SPAN
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332 CLASS="STRUCTNAME"
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333 >surface</SPAN
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334 >-><TT
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335 CLASS="STRUCTFIELD"
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336 ><I
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337 >format</I
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338 ></TT
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339 >-><TT
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340 CLASS="STRUCTFIELD"
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341 ><I
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342 >palette</I
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343 ></TT
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344 >-><TT
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345 CLASS="STRUCTFIELD"
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346 ><I
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347 >colors</I
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348 ></TT
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349 >. Like so:
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350 <PRE
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351 CLASS="PROGRAMLISTING"
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352 >SDL_Surface *surface;
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353 SDL_PixelFormat *fmt;
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354 SDL_Color *color;
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355 Uint8 index;
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356
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357 .
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358 .
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359
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360 /* Create surface */
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361 .
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362 .
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363 fmt=surface->format;
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364
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365 /* Check the bitdepth of the surface */
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366 if(fmt->BitsPerPixel!=8){
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367 fprintf(stderr, "Not an 8-bit surface.\n");
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368 return(-1);
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369 }
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370
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371 /* Lock the surface */
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372 SDL_LockSurface(surface);
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373
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374 /* Get the topleft pixel */
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375 index=*(Uint8 *)surface->pixels;
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376 color=fmt->palette->colors[index];
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377
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378 /* Unlock the surface */
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379 SDL_UnlockSurface(surface);
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380 printf("Pixel Color-> Red: %d, Green: %d, Blue: %d. Index: %d\n",
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381 color->r, color->g, color->b, index);
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382 .
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383 .</PRE
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384 ></P
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385 ><P
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386 >Pixel formats above 8-bit are an entirely different experience. They are considered to be "TrueColor" formats and the color information is stored in the pixels themselves, not in a palette (packed-pixel). The mask, shift and loss fields tell us how the color information is encoded. The mask fields allow us to isolate each color component, the shift fields tell us how far left we have to shift the masked value and the loss fields tell us for far right we have to shift the final value to convert it to a full 8-bit color component.
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387 <PRE
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388 CLASS="PROGRAMLISTING"
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389 >/* Extracting color components from a 32-bit color value */
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390 SDL_PixelFormat *fmt;
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391 SDL_Surface *surface;
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392 Uint32 temp, pixel;
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393 Uint8 red, green, blue, alpha;
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394 .
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395 .
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396 .
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397 fmt=surface->format;
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398 SDL_LockSurface(surface);
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399 pixel=(Uint32*)surface->pixels;
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400 SDL_UnlockSurface(surface);
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401
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402 /* Get Red component */
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403 temp=pixel&fmt->Rmask; /* Isolate red component */
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404 temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */
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405 temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */
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406 red=(Uint8)temp;
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407
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408 /* Get Green component */
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409 temp=pixel&fmt->Gmask; /* Isolate green component */
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410 temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */
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411 temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */
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412 green=(Uint8)temp;
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413
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414 /* Get Blue component */
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415 temp=pixel&fmt->Bmask; /* Isolate blue component */
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416 temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */
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417 temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */
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418 blue=(Uint8)temp;
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419
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420 /* Get Alpha component */
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421 temp=pixel&fmt->Amask; /* Isolate alpha component */
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422 temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */
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423 temp=temp<<fmt->Aloss; /* Expand to a full 8-bit number */
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424 alpha=(Uint8)temp;
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425
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426 printf("Pixel Color -> R: %d, G: %d, B: %d, A: %d\n", red, green, blue, alpha);
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427 .
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428 .
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429 .</PRE
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430 ></P
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431 ></DIV
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432 ><DIV
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433 CLASS="REFSECT1"
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434 ><A
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435 NAME="AEN2751"
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436 ></A
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437 ><H2
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438 >See Also</H2
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439 ><P
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440 ><A
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441 HREF="sdlsurface.html"
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442 ><SPAN
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443 CLASS="STRUCTNAME"
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444 >SDL_Surface</SPAN
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445 ></A
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446 >,
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447 <A
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448 HREF="sdlmaprgb.html"
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449 ><TT
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450 CLASS="FUNCTION"
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451 >SDL_MapRGB</TT
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452 ></A
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453 ></P
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454 ></DIV
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455 ><DIV
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456 CLASS="NAVFOOTER"
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457 ><HR
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458 ALIGN="LEFT"
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459 WIDTH="100%"><TABLE
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460 WIDTH="100%"
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461 BORDER="0"
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462 CELLPADDING="0"
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463 CELLSPACING="0"
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464 ><TR
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465 ><TD
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466 WIDTH="33%"
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467 ALIGN="left"
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468 VALIGN="top"
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469 ><A
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470 HREF="sdlpalette.html"
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471 >Prev</A
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472 ></TD
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473 ><TD
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474 WIDTH="34%"
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475 ALIGN="center"
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476 VALIGN="top"
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477 ><A
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478 HREF="index.html"
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479 >Home</A
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480 ></TD
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481 ><TD
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482 WIDTH="33%"
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483 ALIGN="right"
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484 VALIGN="top"
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485 ><A
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486 HREF="sdlsurface.html"
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487 >Next</A
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488 ></TD
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489 ></TR
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490 ><TR
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491 ><TD
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492 WIDTH="33%"
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493 ALIGN="left"
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494 VALIGN="top"
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495 >SDL_Palette</TD
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496 ><TD
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497 WIDTH="34%"
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498 ALIGN="center"
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499 VALIGN="top"
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500 ><A
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501 HREF="video.html"
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502 >Up</A
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503 ></TD
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504 ><TD
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505 WIDTH="33%"
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506 ALIGN="right"
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507 VALIGN="top"
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508 >SDL_Surface</TD
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509 ></TR
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510 ></TABLE
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511 ></DIV
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512 ></BODY
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513 ></HTML
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514 > |
