annotate docs/html/sdlpixelformat.html @ 4106:12bb6311fd5d SDL-1.2

Hans de Goede fixed bug #495 When running boswars: http://www.boswars.org/ on a machine with intel integrathed graphics it crashes when it tries to play the initial theora splashscreen video: X Error of failed request: BadAlloc (insufficient resources for operation) Major opcode of failed request: 140 (XVideo) Minor opcode of failed request: 19 () Serial number of failed request: 25 Current serial number in output stream: 26 boswars: xcb_xlib.c:41: xcb_xlib_lock: Assertion `!c->xlib.lock' failed. Aborted I recognized this problem from a few years back, when I encountered it while working on the Xv blitter for xmame. The problem is that for some reason creation the Xvport and XvImage succeeds, and failure (lack of resources / hw capability?) is only indicated during the first XvPut[Shm]Image. I've written a patch for SDL using the work around for this I developed for xmame (and which is still used successfully in xmame after many years of usage). I'll admit it isn't very pretty, but after investigating several possibilities this was the best option, any other fixes would need changes to the SDL api and abi.
author Sam Lantinga <slouken@libsdl.org>
date Sat, 29 Dec 2007 02:23:48 +0000
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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 1.76b+
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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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13 TITLE="Video"
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16 TITLE="SDL_Palette"
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17 HREF="sdlpalette.html"><LINK
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19 TITLE="SDL_Surface"
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20 HREF="sdlsurface.html"></HEAD
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24 TEXT="#000000"
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25 LINK="#0000ee"
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30 ><TABLE
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31 SUMMARY="Header navigation table"
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33 BORDER="0"
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34 CELLPADDING="0"
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35 CELLSPACING="0"
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36 ><TR
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37 ><TH
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38 COLSPAN="3"
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39 ALIGN="center"
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40 >SDL Library Documentation</TH
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41 ></TR
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44 WIDTH="10%"
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47 ><A
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48 HREF="sdlpalette.html"
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49 ACCESSKEY="P"
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50 >Prev</A
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51 ></TD
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52 ><TD
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58 WIDTH="10%"
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60 VALIGN="bottom"
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61 ><A
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62 HREF="sdlsurface.html"
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63 ACCESSKEY="N"
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64 >Next</A
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65 ></TD
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67 ></TABLE
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70 WIDTH="100%"></DIV
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71 ><H1
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72 ><A
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73 NAME="SDLPIXELFORMAT"
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74 ></A
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75 >SDL_PixelFormat</H1
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76 ><DIV
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77 CLASS="REFNAMEDIV"
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78 ><A
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80 ></A
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81 ><H2
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82 >Name</H2
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83 >SDL_PixelFormat&nbsp;--&nbsp;Stores surface format information</DIV
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84 ><DIV
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85 CLASS="REFSECT1"
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86 ><A
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89 ><H2
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90 >Structure Definition</H2
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91 ><PRE
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92 CLASS="PROGRAMLISTING"
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93 >typedef struct SDL_PixelFormat {
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94 SDL_Palette *palette;
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95 Uint8 BitsPerPixel;
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96 Uint8 BytesPerPixel;
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97 Uint8 Rloss, Gloss, Bloss, Aloss;
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98 Uint8 Rshift, Gshift, Bshift, Ashift;
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99 Uint32 Rmask, Gmask, Bmask, Amask;
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100 Uint32 colorkey;
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101 Uint8 alpha;
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102 } SDL_PixelFormat;</PRE
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103 ></DIV
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104 ><DIV
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105 CLASS="REFSECT1"
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106 ><A
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108 ></A
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109 ><H2
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110 >Structure Data</H2
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111 ><DIV
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112 CLASS="INFORMALTABLE"
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113 ><A
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116 ><P
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117 ></P
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118 ><TABLE
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119 BORDER="0"
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120 CLASS="CALSTABLE"
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121 ><TBODY
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122 ><TR
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123 ><TD
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124 ALIGN="LEFT"
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126 ><TT
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127 CLASS="STRUCTFIELD"
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128 ><I
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129 >palette</I
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130 ></TT
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131 ></TD
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132 ><TD
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133 ALIGN="LEFT"
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134 VALIGN="TOP"
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135 >Pointer to the <A
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136 HREF="sdlpalette.html"
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137 >palette</A
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138 >, or <TT
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139 CLASS="LITERAL"
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140 >NULL</TT
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141 > if the <TT
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142 CLASS="STRUCTFIELD"
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143 ><I
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144 >BitsPerPixel</I
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145 ></TT
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146 >&#62;8</TD
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147 ></TR
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148 ><TR
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149 ><TD
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150 ALIGN="LEFT"
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151 VALIGN="TOP"
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152 ><TT
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153 CLASS="STRUCTFIELD"
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154 ><I
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155 >BitsPerPixel</I
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156 ></TT
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157 ></TD
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158 ><TD
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159 ALIGN="LEFT"
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160 VALIGN="TOP"
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161 >The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32.</TD
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162 ></TR
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163 ><TR
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164 ><TD
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165 ALIGN="LEFT"
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166 VALIGN="TOP"
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167 ><TT
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168 CLASS="STRUCTFIELD"
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169 ><I
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170 >BytesPerPixel</I
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171 ></TT
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172 ></TD
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173 ><TD
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174 ALIGN="LEFT"
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175 VALIGN="TOP"
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176 >The number of bytes used to represent each pixel in a surface. Usually one to four.</TD
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177 ></TR
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178 ><TR
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179 ><TD
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180 ALIGN="LEFT"
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181 VALIGN="TOP"
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182 ><TT
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183 CLASS="STRUCTFIELD"
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184 ><I
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185 >[RGBA]mask</I
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186 ></TT
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187 ></TD
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188 ><TD
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189 ALIGN="LEFT"
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190 VALIGN="TOP"
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191 >Binary mask used to retrieve individual color values</TD
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192 ></TR
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193 ><TR
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194 ><TD
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195 ALIGN="LEFT"
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196 VALIGN="TOP"
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197 ><TT
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198 CLASS="STRUCTFIELD"
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199 ><I
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200 >[RGBA]loss</I
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201 ></TT
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202 ></TD
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203 ><TD
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204 ALIGN="LEFT"
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205 VALIGN="TOP"
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206 >Precision loss of each color component (2<SUP
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207 >[RGBA]loss</SUP
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208 >)</TD
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209 ></TR
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210 ><TR
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211 ><TD
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212 ALIGN="LEFT"
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213 VALIGN="TOP"
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214 ><TT
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215 CLASS="STRUCTFIELD"
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216 ><I
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217 >[RGBA]shift</I
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218 ></TT
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219 ></TD
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220 ><TD
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221 ALIGN="LEFT"
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222 VALIGN="TOP"
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223 >Binary left shift of each color component in the pixel value</TD
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224 ></TR
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225 ><TR
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226 ><TD
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227 ALIGN="LEFT"
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228 VALIGN="TOP"
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229 ><TT
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230 CLASS="STRUCTFIELD"
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231 ><I
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232 >colorkey</I
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233 ></TT
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234 ></TD
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235 ><TD
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236 ALIGN="LEFT"
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237 VALIGN="TOP"
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238 >Pixel value of transparent pixels</TD
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239 ></TR
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240 ><TR
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241 ><TD
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242 ALIGN="LEFT"
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243 VALIGN="TOP"
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244 ><TT
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245 CLASS="STRUCTFIELD"
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246 ><I
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247 >alpha</I
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248 ></TT
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249 ></TD
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250 ><TD
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251 ALIGN="LEFT"
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252 VALIGN="TOP"
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253 >Overall surface alpha value</TD
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254 ></TR
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255 ></TBODY
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256 ></TABLE
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257 ><P
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258 ></P
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259 ></DIV
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260 ></DIV
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261 ><DIV
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262 CLASS="REFSECT1"
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263 ><A
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355632dca928 Updated SDL HTML documentation
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264 NAME="AEN3225"
0
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265 ></A
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266 ><H2
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267 >Description</H2
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268 ><P
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269 >A <SPAN
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270 CLASS="STRUCTNAME"
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271 >SDL_PixelFormat</SPAN
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272 > describes the format of the pixel data stored at the <TT
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273 CLASS="STRUCTFIELD"
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274 ><I
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275 >pixels</I
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276 ></TT
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277 > field of a <A
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278 HREF="sdlsurface.html"
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279 ><SPAN
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280 CLASS="STRUCTNAME"
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281 >SDL_Surface</SPAN
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282 ></A
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283 >. Every surface stores a <SPAN
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284 CLASS="STRUCTNAME"
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285 >SDL_PixelFormat</SPAN
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286 > in the <TT
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287 CLASS="STRUCTFIELD"
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288 ><I
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289 >format</I
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290 ></TT
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291 > field.</P
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292 ><P
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293 >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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294 ><P
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295 >8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 <TT
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296 CLASS="STRUCTFIELD"
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297 ><I
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298 >BitsPerPixel</I
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299 ></TT
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300 > and 1 <TT
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301 CLASS="STRUCTFIELD"
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302 ><I
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303 >BytesPerPixel</I
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304 ></TT
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305 >. Since <TT
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306 CLASS="STRUCTFIELD"
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307 ><I
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308 >BytesPerPixel</I
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309 ></TT
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310 > is 1, all pixels are represented by a Uint8 which contains an index into <TT
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311 CLASS="STRUCTFIELD"
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312 ><I
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313 >palette</I
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314 ></TT
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315 >-&#62;<TT
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316 CLASS="STRUCTFIELD"
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317 ><I
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318 >colors</I
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319 ></TT
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320 >. So, to determine the color of a pixel in a 8-bit surface: we read the color index from <SPAN
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321 CLASS="STRUCTNAME"
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322 >surface</SPAN
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323 >-&#62;<TT
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324 CLASS="STRUCTFIELD"
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325 ><I
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326 >pixels</I
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327 ></TT
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328 > and we use that index to read the <A
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329 HREF="sdlcolor.html"
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330 ><SPAN
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331 CLASS="STRUCTNAME"
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332 >SDL_Color</SPAN
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333 ></A
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334 > structure from <SPAN
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335 CLASS="STRUCTNAME"
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336 >surface</SPAN
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337 >-&#62;<TT
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338 CLASS="STRUCTFIELD"
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339 ><I
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340 >format</I
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341 ></TT
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342 >-&#62;<TT
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343 CLASS="STRUCTFIELD"
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344 ><I
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345 >palette</I
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346 ></TT
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347 >-&#62;<TT
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348 CLASS="STRUCTFIELD"
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349 ><I
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350 >colors</I
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351 ></TT
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352 >. Like so:
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353 <PRE
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354 CLASS="PROGRAMLISTING"
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355 >SDL_Surface *surface;
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356 SDL_PixelFormat *fmt;
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357 SDL_Color *color;
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358 Uint8 index;
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359
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360 .
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361 .
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362
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363 /* Create surface */
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364 .
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365 .
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366 fmt=surface-&#62;format;
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367
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368 /* Check the bitdepth of the surface */
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369 if(fmt-&#62;BitsPerPixel!=8){
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370 fprintf(stderr, "Not an 8-bit surface.\n");
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371 return(-1);
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372 }
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373
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374 /* Lock the surface */
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375 SDL_LockSurface(surface);
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376
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377 /* Get the topleft pixel */
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378 index=*(Uint8 *)surface-&#62;pixels;
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379 color=fmt-&#62;palette-&#62;colors[index];
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380
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381 /* Unlock the surface */
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382 SDL_UnlockSurface(surface);
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383 printf("Pixel Color-&#62; Red: %d, Green: %d, Blue: %d. Index: %d\n",
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384 color-&#62;r, color-&#62;g, color-&#62;b, index);
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385 .
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386 .</PRE
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387 ></P
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388 ><P
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389 >Pixel formats above 8-bit are an entirely different experience. They are
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390 considered to be "TrueColor" formats and the color information is stored in the
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391 pixels themselves, not in a palette. The mask, shift and loss fields tell us
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392 how the color information is encoded. The mask fields allow us to isolate each
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393 color component, the shift fields tell us the number of bits to the right of
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394 each component in the pixel value and the loss fields tell us the number of
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395 bits lost from each component when packing 8-bit color component in a pixel.
0
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396 <PRE
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397 CLASS="PROGRAMLISTING"
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398 >/* Extracting color components from a 32-bit color value */
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399 SDL_PixelFormat *fmt;
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400 SDL_Surface *surface;
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401 Uint32 temp, pixel;
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402 Uint8 red, green, blue, alpha;
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403 .
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404 .
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405 .
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406 fmt=surface-&#62;format;
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407 SDL_LockSurface(surface);
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408 pixel=*((Uint32*)surface-&#62;pixels);
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409 SDL_UnlockSurface(surface);
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410
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411 /* Get Red component */
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412 temp=pixel&#38;fmt-&#62;Rmask; /* Isolate red component */
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413 temp=temp&#62;&#62;fmt-&#62;Rshift;/* Shift it down to 8-bit */
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414 temp=temp&#60;&#60;fmt-&#62;Rloss; /* Expand to a full 8-bit number */
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415 red=(Uint8)temp;
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416
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417 /* Get Green component */
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418 temp=pixel&#38;fmt-&#62;Gmask; /* Isolate green component */
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419 temp=temp&#62;&#62;fmt-&#62;Gshift;/* Shift it down to 8-bit */
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420 temp=temp&#60;&#60;fmt-&#62;Gloss; /* Expand to a full 8-bit number */
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421 green=(Uint8)temp;
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422
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423 /* Get Blue component */
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424 temp=pixel&#38;fmt-&#62;Bmask; /* Isolate blue component */
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425 temp=temp&#62;&#62;fmt-&#62;Bshift;/* Shift it down to 8-bit */
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426 temp=temp&#60;&#60;fmt-&#62;Bloss; /* Expand to a full 8-bit number */
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427 blue=(Uint8)temp;
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428
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429 /* Get Alpha component */
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430 temp=pixel&#38;fmt-&#62;Amask; /* Isolate alpha component */
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431 temp=temp&#62;&#62;fmt-&#62;Ashift;/* Shift it down to 8-bit */
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432 temp=temp&#60;&#60;fmt-&#62;Aloss; /* Expand to a full 8-bit number */
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433 alpha=(Uint8)temp;
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434
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435 printf("Pixel Color -&#62; R: %d, G: %d, B: %d, A: %d\n", red, green, blue, alpha);
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436 .
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437 .
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438 .</PRE
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439 ></P
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440 ></DIV
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441 ><DIV
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442 CLASS="REFSECT1"
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443 ><A
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444 NAME="AEN3252"
0
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445 ></A
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446 ><H2
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447 >See Also</H2
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448 ><P
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449 ><A
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450 HREF="sdlsurface.html"
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451 ><SPAN
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452 CLASS="STRUCTNAME"
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453 >SDL_Surface</SPAN
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454 ></A
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455 >,
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456 <A
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457 HREF="sdlmaprgb.html"
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458 ><TT
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459 CLASS="FUNCTION"
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460 >SDL_MapRGB</TT
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461 ></A
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462 ></P
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463 ></DIV
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464 ><DIV
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465 CLASS="NAVFOOTER"
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466 ><HR
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diff changeset
467 ALIGN="LEFT"
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468 WIDTH="100%"><TABLE
803
355632dca928 Updated SDL HTML documentation
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diff changeset
469 SUMMARY="Footer navigation table"
0
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470 WIDTH="100%"
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471 BORDER="0"
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472 CELLPADDING="0"
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473 CELLSPACING="0"
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474 ><TR
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475 ><TD
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476 WIDTH="33%"
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477 ALIGN="left"
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Sam Lantinga <slouken@lokigames.com>
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478 VALIGN="top"
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479 ><A
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480 HREF="sdlpalette.html"
803
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diff changeset
481 ACCESSKEY="P"
0
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482 >Prev</A
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483 ></TD
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484 ><TD
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parents:
diff changeset
485 WIDTH="34%"
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diff changeset
486 ALIGN="center"
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487 VALIGN="top"
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488 ><A
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489 HREF="index.html"
803
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diff changeset
490 ACCESSKEY="H"
0
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491 >Home</A
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492 ></TD
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493 ><TD
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494 WIDTH="33%"
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diff changeset
495 ALIGN="right"
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496 VALIGN="top"
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497 ><A
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498 HREF="sdlsurface.html"
803
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diff changeset
499 ACCESSKEY="N"
0
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500 >Next</A
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501 ></TD
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502 ></TR
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503 ><TR
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504 ><TD
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parents:
diff changeset
505 WIDTH="33%"
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diff changeset
506 ALIGN="left"
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507 VALIGN="top"
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508 >SDL_Palette</TD
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509 ><TD
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510 WIDTH="34%"
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Sam Lantinga <slouken@lokigames.com>
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diff changeset
511 ALIGN="center"
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Sam Lantinga <slouken@lokigames.com>
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512 VALIGN="top"
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513 ><A
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514 HREF="video.html"
803
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diff changeset
515 ACCESSKEY="U"
0
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516 >Up</A
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517 ></TD
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518 ><TD
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519 WIDTH="33%"
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520 ALIGN="right"
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521 VALIGN="top"
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522 >SDL_Surface</TD
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523 ></TR
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524 ></TABLE
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525 ></DIV
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526 ></BODY
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527 ></HTML
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e867f327aa54 *** empty log message ***
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528 >