/
sdllocksurface.html
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sdllocksurface.html
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<HTML
><HEAD
><TITLE
>SDL_LockSurface</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
"><LINK
REL="HOME"
TITLE="SDL Library Documentation"
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REL="UP"
TITLE="Video"
HREF="video.html"><LINK
REL="PREVIOUS"
TITLE="SDL_FreeSurface"
HREF="sdlfreesurface.html"><LINK
REL="NEXT"
TITLE="SDL_UnlockSurface"
HREF="sdlunlocksurface.html"></HEAD
><BODY
CLASS="REFENTRY"
BGCOLOR="#FFF8DC"
TEXT="#000000"
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VLINK="#551a8b"
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><DIV
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><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><H1
><A
NAME="SDLLOCKSURFACE"
></A
>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
></P
></DIV
><DIV
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>Home</A
></TD
><TD
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><A
HREF="sdlunlocksurface.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>SDL_FreeSurface</TD
><TD
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><A
HREF="video.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
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>SDL_UnlockSurface</TD
></TR
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></DIV
></BODY
></HTML
>