view docs/html/sdlglgetprocaddress.html @ 1259:36f24cdfcda7

te: Thu, 17 Apr 2003 11:25:26 -0700 From: "Jim" Subject: [SDL] Frame buffer patches... Would seem that GCC 3.2.2 promotes all signed values to unsigned if any single vlaue is unsigned in an expression... for instance when calculating an elo touch position....evertyhign is an (int) except for cach_vinfo.xres which is unsigned. THerefore if y ou reverse the SDL_ELO_MIN_X and SDL_ELO_MAX_X values the resulging negative value pegs the expression to it's max. Attached it the accumu lated patch to typecast the unsigned values to (int) - *dx = (cache_vinfo.xres - (cache_vinfo.xres * (input_x - ELO_MIN_X)) / width); + *dx = ((int)cache_vinfo.xres - ((int)cache_vinfo.xres * (input_x - ELO_MIN_X)) / width); and also to provide quite failure to operations which have the screen currently locked... The touch screen I'm using the original values were exactly opposite of any position I touched on the screen - evaluating the math the expr ession SHOULD have handled reversing the min and max values - and after casting the unsigned .xres and .yres to a signed int - worked well. .. Jim
author Sam Lantinga <slouken@libsdl.org>
date Tue, 24 Jan 2006 06:36:43 +0000
parents 355632dca928
children
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>SDL_GL_GetProcAddress</TITLE
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>SDL_GL_GetProcAddress</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN2678"
></A
><H2
>Name</H2
>SDL_GL_GetProcAddress&nbsp;--&nbsp;Get the address of a GL function</DIV
><DIV
CLASS="REFSYNOPSISDIV"
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><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
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><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include "SDL.h"</PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void *<B
CLASS="FSFUNC"
>SDL_GL_GetProcAddress</B
></CODE
>(const char* proc);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN2688"
></A
><H2
>Description</H2
><P
>Returns the address of the GL function <TT
CLASS="PARAMETER"
><I
>proc</I
></TT
>, or <SPAN
CLASS="RETURNVALUE"
>NULL</SPAN
> if the function is not found. If the GL library is loaded at runtime, with <A
HREF="sdlglloadlibrary.html"
><TT
CLASS="FUNCTION"
>SDL_GL_LoadLibrary</TT
></A
>, then <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>all</I
></SPAN
> GL functions must be retrieved this way. Usually this is used to retrieve function pointers to OpenGL extensions.</P
></DIV
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><A
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><H2
>Example</H2
><PRE
CLASS="PROGRAMLISTING"
>typedef void (*GL_ActiveTextureARB_Func)(unsigned int);
GL_ActiveTextureARB_Func glActiveTextureARB_ptr = 0;
int has_multitexture=1;
.
.
.
/* Get function pointer */
glActiveTextureARB_ptr=(GL_ActiveTextureARB_Func) SDL_GL_GetProcAddress("glActiveTextureARB");

/* Check for a valid function ptr */
if(!glActiveTextureARB_ptr){
  fprintf(stderr, "Multitexture Extensions not present.\n");
  has_multitexture=0;
}
.
.
.
.
if(has_multitexture){
  glActiveTextureARB_ptr(GL_TEXTURE0_ARB);
  .
  .
}
else{
  .
  .
}</PRE
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