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Date: Sat, 27 Nov 2004 13:35:43 +0100 From: "Martin Bickel" Subject: [SDL] Patch: fixing uninitilized palette while running Valgrind over my application I found the following problem in SDL: The function MapNto1 allocates SDL_Color colors[256] but does not initialize it. SDL_DitherColors is then called which initialized the r, g and b component, but not the 'unused' component of each color. When Map1to1 is called from MapNto1, it runs a memcmp on the colors, which also evaluates the unused component and therefor returns differences much more often than necessary. So the 'unused' component of SDL_Color should be initialized. This patch does this by calling memset for the whole array in MapNto1 .
author Sam Lantinga <slouken@libsdl.org>
date Tue, 30 Nov 2004 14:28:20 +0000
parents 355632dca928
children
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<HTML
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>SDL_CreateRGBSurface</TITLE
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><H1
><A
NAME="SDLCREATERGBSURFACE"
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>SDL_CreateRGBSurface</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN1773"
></A
><H2
>Name</H2
>SDL_CreateRGBSurface&nbsp;--&nbsp;Create an empty SDL_Surface</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN1776"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN1777"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include "SDL.h"</PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>SDL_Surface *<B
CLASS="FSFUNC"
>SDL_CreateRGBSurface</B
></CODE
>(Uint32 flags, int width, int height, int depth, Uint32 Rmask, Uint32 Gmask, Uint32 Bmask, Uint32 Amask);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN1783"
></A
><H2
>Description</H2
><P
>Allocate an empty surface (must be called after <A
HREF="sdlsetvideomode.html"
>SDL_SetVideoMode</A
>)</P
><P
>If <TT
CLASS="PARAMETER"
><I
>depth</I
></TT
> is 8 bits an empty palette is allocated for the surface, otherwise a 'packed-pixel' <A
HREF="sdlpixelformat.html"
><SPAN
CLASS="STRUCTNAME"
>SDL_PixelFormat</SPAN
></A
> is created using the <TT
CLASS="PARAMETER"
><I
>[RGBA]mask</I
></TT
>'s provided (see <A
HREF="sdlpixelformat.html"
><SPAN
CLASS="STRUCTNAME"
>SDL_PixelFormat</SPAN
></A
>). The <TT
CLASS="PARAMETER"
><I
>flags</I
></TT
> specifies the type of surface that should be created, it is an OR'd combination of the following possible values.</P
><DIV
CLASS="INFORMALTABLE"
><A
NAME="AEN1795"
></A
><P
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>SDL_SWSURFACE</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>SDL will create the surface in system memory. This improves the performance of pixel level access, however you may not be able to take advantage of some types of hardware blitting.</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>SDL_HWSURFACE</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>SDL will attempt to create the surface in video memory. This will allow SDL to take advantage of Video-&#62;Video blits (which are often accelerated).</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>This flag turns on colourkeying for blits from this surface. If
<TT
CLASS="LITERAL"
>SDL_HWSURFACE</TT
> is also specified and colourkeyed blits
are hardware-accelerated, then SDL will attempt to place the surface in
video memory.
Use <A
HREF="sdlsetcolorkey.html"
><TT
CLASS="FUNCTION"
>SDL_SetColorKey</TT
></A
>
to set or clear this flag after surface creation.</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>This flag turns on alpha-blending for blits from this surface. If
<TT
CLASS="LITERAL"
>SDL_HWSURFACE</TT
> is also specified and alpha-blending blits
are hardware-accelerated, then the surface will be placed in video memory if
possible.
Use <A
HREF="sdlsetalpha.html"
><TT
CLASS="FUNCTION"
>SDL_SetAlpha</TT
></A
> to
set or clear this flag after surface creation.</TD
></TR
></TBODY
></TABLE
><P
></P
></DIV
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>If an alpha-channel is specified (that is, if <TT
CLASS="PARAMETER"
><I
>Amask</I
></TT
> is
nonzero), then the <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
> flag is automatically
set. You may remove this flag by calling 
<A
HREF="sdlsetalpha.html"
><TT
CLASS="FUNCTION"
>SDL_SetAlpha</TT
></A
>
after surface creation.</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN1826"
></A
><H2
>Return Value</H2
><P
>Returns the created surface, or <SPAN
CLASS="RETURNVALUE"
>NULL</SPAN
> upon error.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN1830"
></A
><H2
>Example</H2
><PRE
CLASS="PROGRAMLISTING"
>    /* Create a 32-bit surface with the bytes of each pixel in R,G,B,A order,
       as expected by OpenGL for textures */
    SDL_Surface *surface;
    Uint32 rmask, gmask, bmask, amask;

    /* SDL interprets each pixel as a 32-bit number, so our masks must depend
       on the endianness (byte order) of the machine */
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
    rmask = 0xff000000;
    gmask = 0x00ff0000;
    bmask = 0x0000ff00;
    amask = 0x000000ff;
#else
    rmask = 0x000000ff;
    gmask = 0x0000ff00;
    bmask = 0x00ff0000;
    amask = 0xff000000;
#endif

    surface = SDL_CreateRGBSurface(SDL_SWSURFACE, width, height, 32,
                                   rmask, gmask, bmask, amask);
    if(surface == NULL) {
        fprintf(stderr, "CreateRGBSurface failed: %s\n", SDL_GetError());
        exit(1);
    }</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN1833"
></A
><H2
>See Also</H2
><P
><A
HREF="sdlcreatergbsurfacefrom.html"
><TT
CLASS="FUNCTION"
>SDL_CreateRGBSurfaceFrom</TT
></A
>,
<A
HREF="sdlfreesurface.html"
><TT
CLASS="FUNCTION"
>SDL_FreeSurface</TT
></A
>,
<A
HREF="sdlsetvideomode.html"
><TT
CLASS="FUNCTION"
>SDL_SetVideoMode</TT
></A
>,
<A
HREF="sdllocksurface.html"
><TT
CLASS="FUNCTION"
>SDL_LockSurface</TT
></A
>,
<A
HREF="sdlpixelformat.html"
><SPAN
CLASS="STRUCTNAME"
>SDL_PixelFormat</SPAN
></A
>,
<A
HREF="sdlsurface.html"
><SPAN
CLASS="STRUCTNAME"
>SDL_Surface</SPAN
></A
>
<A
HREF="sdlsetalpha.html"
><TT
CLASS="FUNCTION"
>SDL_SetAlpha</TT
></A
>
<A
HREF="sdlsetcolorkey.html"
><TT
CLASS="FUNCTION"
>SDL_SetColorKey</TT
></A
></P
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