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  72 ><A
  73 NAME="SDLLOCKSURFACE"
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  75 >SDL_LockSurface</H1
  76 ><DIV
  77 CLASS="REFNAMEDIV"
  78 ><A
  79 NAME="AEN1919"
  80 ></A
  81 ><H2
  82 >Name</H2
  83 >SDL_LockSurface&nbsp;--&nbsp;Lock a surface for directly access.</DIV
  84 ><DIV
  85 CLASS="REFSYNOPSISDIV"
  86 ><A
  87 NAME="AEN1922"
  88 ></A
  89 ><H2
  90 >Synopsis</H2
  91 ><DIV
  92 CLASS="FUNCSYNOPSIS"
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  94 NAME="AEN1923"
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  96 ><P
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  98 ><PRE
  99 CLASS="FUNCSYNOPSISINFO"
 100 >#include "SDL.h"</PRE
 101 ><P
 102 ><CODE
 103 ><CODE
 104 CLASS="FUNCDEF"
 105 >int <B
 106 CLASS="FSFUNC"
 107 >SDL_LockSurface</B
 108 ></CODE
 109 >(SDL_Surface *surface);</CODE
 110 ></P
 111 ><P
 112 ></P
 113 ></DIV
 114 ></DIV
 115 ><DIV
 116 CLASS="REFSECT1"
 117 ><A
 118 NAME="AEN1929"
 119 ></A
 120 ><H2
 121 >Description</H2
 122 ><P
 123 ><TT
 124 CLASS="FUNCTION"
 125 >SDL_LockSurface</TT
 126 > sets up a surface for directly
 127 accessing the pixels.  Between calls to <TT
 128 CLASS="FUNCTION"
 129 >SDL_LockSurface</TT
 130 >
 131 and <TT
 132 CLASS="FUNCTION"
 133 >SDL_UnlockSurface</TT
 134 >, you can write to and read from
 135 <TT
 136 CLASS="PARAMETER"
 137 ><I
 138 >surface-&#62;<TT
 139 CLASS="STRUCTFIELD"
 140 ><I
 141 >pixels</I
 142 ></TT
 143 ></I
 144 ></TT
 145 >, using the pixel format stored in
 146 <TT
 147 CLASS="PARAMETER"
 148 ><I
 149 >surface-&#62;<TT
 150 CLASS="STRUCTFIELD"
 151 ><I
 152 >format</I
 153 ></TT
 154 ></I
 155 ></TT
 156 >.  Once you are done accessing the
 157 surface, you should use <TT
 158 CLASS="FUNCTION"
 159 >SDL_UnlockSurface</TT
 160 > to release it.</P
 161 ><P
 162 >Not all surfaces require locking.
 163 If <TT
 164 CLASS="LITERAL"
 165 >SDL_MUSTLOCK</TT
 166 >(<TT
 167 CLASS="PARAMETER"
 168 ><I
 169 >surface</I
 170 ></TT
 171 >)
 172 evaluates to <SPAN
 173 CLASS="RETURNVALUE"
 174 >0</SPAN
 175 >, then you can read and write to the
 176 surface at any time, and the pixel format of the surface will not change. </P
 177 ><P
 178 >No operating system or library calls should be made between lock/unlock
 179 pairs, as critical system locks may be held during this time.</P
 180 ><P
 181 >It should be noted, that since SDL 1.1.8 surface locks are recursive. This means that you can lock a surface multiple times, but each lock must have a match unlock.
 182 <PRE
 183 CLASS="PROGRAMLISTING"
 184 >    .
 185     .
 186     SDL_LockSurface( surface );
 187     .
 188     /* Surface is locked */
 189     /* Direct pixel access on surface here */
 190     .
 191     SDL_LockSurface( surface );
 192     .
 193     /* More direct pixel access on surface */
 194     .
 195     SDL_UnlockSurface( surface );
 196     /* Surface is still locked */
 197     /* Note: Is versions &#60; 1.1.8, the surface would have been */
 198     /* no longer locked at this stage                         */
 199     .
 200     SDL_UnlockSurface( surface );
 201     /* Surface is now unlocked */
 202     .
 203     .</PRE
 204 ></P
 205 ></DIV
 206 ><DIV
 207 CLASS="REFSECT1"
 208 ><A
 209 NAME="AEN1947"
 210 ></A
 211 ><H2
 212 >Return Value</H2
 213 ><P
 214 ><TT
 215 CLASS="FUNCTION"
 216 >SDL_LockSurface</TT
 217 > returns <SPAN
 218 CLASS="RETURNVALUE"
 219 >0</SPAN
 220 >,
 221 or <SPAN
 222 CLASS="RETURNVALUE"
 223 >-1</SPAN
 224 > if the surface couldn't be locked.</P
 225 ></DIV
 226 ><DIV
 227 CLASS="REFSECT1"
 228 ><A
 229 NAME="AEN1953"
 230 ></A
 231 ><H2
 232 >See Also</H2
 233 ><P
 234 ><A
 235 HREF="sdlunlocksurface.html"
 236 ><TT
 237 CLASS="FUNCTION"
 238 >SDL_UnlockSurface</TT
 239 ></A
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