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| >SDL_LockSurface</H1 |
| ><DIV |
| CLASS="REFNAMEDIV" |
| ><A |
| NAME="AEN1919" |
| ></A |
| ><H2 |
| >Name</H2 |
| >SDL_LockSurface -- Lock a surface for directly access.</DIV |
| ><DIV |
| CLASS="REFSYNOPSISDIV" |
| ><A |
| NAME="AEN1922" |
| ></A |
| ><H2 |
| >Synopsis</H2 |
| ><DIV |
| CLASS="FUNCSYNOPSIS" |
| ><A |
| NAME="AEN1923" |
| ></A |
| ><P |
| ></P |
| ><PRE |
| CLASS="FUNCSYNOPSISINFO" |
| >#include "SDL.h"</PRE |
| ><P |
| ><CODE |
| ><CODE |
| CLASS="FUNCDEF" |
| >int <B |
| CLASS="FSFUNC" |
| >SDL_LockSurface</B |
| ></CODE |
| >(SDL_Surface *surface);</CODE |
| ></P |
| ><P |
| ></P |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN1929" |
| ></A |
| ><H2 |
| >Description</H2 |
| ><P |
| ><TT |
| CLASS="FUNCTION" |
| >SDL_LockSurface</TT |
| > sets up a surface for directly |
| accessing the pixels. Between calls to <TT |
| CLASS="FUNCTION" |
| >SDL_LockSurface</TT |
| > |
| and <TT |
| CLASS="FUNCTION" |
| >SDL_UnlockSurface</TT |
| >, you can write to and read from |
| <TT |
| CLASS="PARAMETER" |
| ><I |
| >surface-><TT |
| CLASS="STRUCTFIELD" |
| ><I |
| >pixels</I |
| ></TT |
| ></I |
| ></TT |
| >, using the pixel format stored in |
| <TT |
| CLASS="PARAMETER" |
| ><I |
| >surface-><TT |
| CLASS="STRUCTFIELD" |
| ><I |
| >format</I |
| ></TT |
| ></I |
| ></TT |
| >. Once you are done accessing the |
| surface, you should use <TT |
| CLASS="FUNCTION" |
| >SDL_UnlockSurface</TT |
| > to release it.</P |
| ><P |
| >Not all surfaces require locking. |
| If <TT |
| CLASS="LITERAL" |
| >SDL_MUSTLOCK</TT |
| >(<TT |
| CLASS="PARAMETER" |
| ><I |
| >surface</I |
| ></TT |
| >) |
| evaluates to <SPAN |
| CLASS="RETURNVALUE" |
| >0</SPAN |
| >, then you can read and write to the |
| surface at any time, and the pixel format of the surface will not change. </P |
| ><P |
| >No operating system or library calls should be made between lock/unlock |
| pairs, as critical system locks may be held during this time.</P |
| ><P |
| >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. |
| <PRE |
| CLASS="PROGRAMLISTING" |
| > . |
| . |
| SDL_LockSurface( surface ); |
| . |
| /* Surface is locked */ |
| /* Direct pixel access on surface here */ |
| . |
| SDL_LockSurface( surface ); |
| . |
| /* More direct pixel access on surface */ |
| . |
| SDL_UnlockSurface( surface ); |
| /* Surface is still locked */ |
| /* Note: Is versions < 1.1.8, the surface would have been */ |
| /* no longer locked at this stage */ |
| . |
| SDL_UnlockSurface( surface ); |
| /* Surface is now unlocked */ |
| . |
| .</PRE |
| ></P |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN1947" |
| ></A |
| ><H2 |
| >Return Value</H2 |
| ><P |
| ><TT |
| CLASS="FUNCTION" |
| >SDL_LockSurface</TT |
| > returns <SPAN |
| CLASS="RETURNVALUE" |
| >0</SPAN |
| >, |
| or <SPAN |
| CLASS="RETURNVALUE" |
| >-1</SPAN |
| > if the surface couldn't be locked.</P |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN1953" |
| ></A |
| ><H2 |
| >See Also</H2 |
| ><P |
| ><A |
| HREF="sdlunlocksurface.html" |
| ><TT |
| CLASS="FUNCTION" |
| >SDL_UnlockSurface</TT |
| ></A |
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