Mercurial > sdl-ios-xcode
view docs/html/sdlsetalpha.html @ 1303:52b5afd7ecee
Date: Tue, 05 Jul 2005 21:43:26 +1000
From: Sean Childs
Subject: [SDL] Compiling SDL 1.2.8 with the free Borland compiler
When compiling SDL 1.2.8 with the free Borland compiler, I received this
error (there is a similar error that occurs in
src\video\windx5\sdl_dx5events.c):
Error E2342 ..\..\src\video\windib\sdl_dibevents.c 189: Type mismatch in
parameter 'lpPrevWndFunc' (wanted 'int (__stdcall *)()', got 'long
(__stdcall *)(void *,unsigned int,unsigned int,long)') in function
DIB_HandleMessage
I checked the MSDN library at:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winui/winui/
windowsuserinterface/windowing/windowprocedures/windowprocedurereference/wind
owprocedurefunctions/callwindowproc.asp
and it had this to say:
If STRICT is not defined, the lpPrevWndFunc parameter has the data type
FARPROC. The FARPROC type is declared as follows:
int (FAR WINAPI * FARPROC) ()
In C, the FARPROC declaration indicates a callback function that has an
unspecified parameter list. In C++, however, the empty parameter list in
the declaration indicates that a function has no parameters. This subtle
distinction can break careless code. Following is one way to handle this
situation:
#ifdef STRICT
WNDPROC MyWindowProcedure
#else
FARPROC MyWindowProcedure
#endif
...
lResult = CallWindowProc(MyWindowProcedure, ...)
author | Sam Lantinga <slouken@libsdl.org> |
---|---|
date | Tue, 31 Jan 2006 15:30:42 +0000 (2006-01-31) |
parents | 355632dca928 |
children |
line wrap: on
line source
<HTML ><HEAD ><TITLE >SDL_SetAlpha</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="SDL Library Documentation" HREF="index.html"><LINK REL="UP" TITLE="Video" HREF="video.html"><LINK REL="PREVIOUS" TITLE="SDL_SetColorKey" HREF="sdlsetcolorkey.html"><LINK REL="NEXT" TITLE="SDL_SetClipRect" HREF="sdlsetcliprect.html"></HEAD ><BODY CLASS="REFENTRY" BGCOLOR="#FFF8DC" TEXT="#000000" LINK="#0000ee" VLINK="#551a8b" ALINK="#ff0000" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >SDL Library Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="sdlsetcolorkey.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="sdlsetcliprect.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="SDLSETALPHA" ></A >SDL_SetAlpha</H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN2096" ></A ><H2 >Name</H2 >SDL_SetAlpha -- Adjust the alpha properties of a surface</DIV ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN2099" ></A ><H2 >Synopsis</H2 ><DIV CLASS="FUNCSYNOPSIS" ><A NAME="AEN2100" ></A ><P ></P ><PRE CLASS="FUNCSYNOPSISINFO" >#include "SDL.h"</PRE ><P ><CODE ><CODE CLASS="FUNCDEF" >int <B CLASS="FSFUNC" >SDL_SetAlpha</B ></CODE >(SDL_Surface *surface, Uint32 flag, Uint8 alpha);</CODE ></P ><P ></P ></DIV ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN2106" ></A ><H2 >Description</H2 ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B >This function and the semantics of SDL alpha blending have changed since version 1.1.4. Up until version 1.1.5, an alpha value of 0 was considered opaque and a value of 255 was considered transparent. This has now been inverted: 0 (<TT CLASS="LITERAL" >SDL_ALPHA_TRANSPARENT</TT >) is now considered transparent and 255 (<TT CLASS="LITERAL" >SDL_ALPHA_OPAQUE</TT >) is now considered opaque.</P ></BLOCKQUOTE ></DIV ><P ><TT CLASS="FUNCTION" >SDL_SetAlpha</TT > is used for setting the per-surface alpha value and/or enabling and disabling alpha blending.</P ><P >The<TT CLASS="PARAMETER" ><I >surface</I ></TT > parameter specifies which surface whose alpha attributes you wish to adjust. <TT CLASS="PARAMETER" ><I >flags</I ></TT > is used to specify whether alpha blending should be used (<TT CLASS="LITERAL" >SDL_SRCALPHA</TT >) and whether the surface should use RLE acceleration for blitting (<TT CLASS="LITERAL" >SDL_RLEACCEL</TT >). <TT CLASS="PARAMETER" ><I >flags</I ></TT > can be an OR'd combination of these two options, one of these options or 0. If <TT CLASS="LITERAL" >SDL_SRCALPHA</TT > is not passed as a flag then all alpha information is ignored when blitting the surface. The <TT CLASS="PARAMETER" ><I >alpha</I ></TT > parameter is the per-surface alpha value; a surface need not have an alpha channel to use per-surface alpha and blitting can still be accelerated with <TT CLASS="LITERAL" >SDL_RLEACCEL</TT >.</P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B >The per-surface alpha value of 128 is considered a special case and is optimised, so it's much faster than other per-surface values.</P ></BLOCKQUOTE ></DIV ><P >Alpha effects surface blitting in the following ways:</P ><DIV CLASS="INFORMALTABLE" ><A NAME="AEN2126" ></A ><P ></P ><TABLE BORDER="0" CLASS="CALSTABLE" ><TBODY ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGBA->RGB with <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The source is alpha-blended with the destination, using the alpha channel. <TT CLASS="LITERAL" >SDL_SRCCOLORKEY</TT > and the per-surface alpha are ignored.</P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGBA->RGB without <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The RGB data is copied from the source. The source alpha channel and the per-surface alpha value are ignored.</P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGB->RGBA with <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The source is alpha-blended with the destination using the per-surface alpha value. If <TT CLASS="LITERAL" >SDL_SRCCOLORKEY</TT > is set, only the pixels not matching the colorkey value are copied. The alpha channel of the copied pixels is set to opaque.</P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGB->RGBA without <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The RGB data is copied from the source and the alpha value of the copied pixels is set to opaque. If <TT CLASS="LITERAL" >SDL_SRCCOLORKEY</TT > is set, only the pixels not matching the colorkey value are copied. </P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGBA->RGBA with <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The source is alpha-blended with the destination using the source alpha channel. The alpha channel in the destination surface is left untouched. <TT CLASS="LITERAL" >SDL_SRCCOLORKEY</TT > is ignored.</P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGBA->RGBA without <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The RGBA data is copied to the destination surface. If <TT CLASS="LITERAL" >SDL_SRCCOLORKEY</TT > is set, only the pixels not matching the colorkey value are copied.</P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGB->RGB with <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The source is alpha-blended with the destination using the per-surface alpha value. If <TT CLASS="LITERAL" >SDL_SRCCOLORKEY</TT > is set, only the pixels not matching the colorkey value are copied.</P ></TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" >RGB->RGB without <TT CLASS="LITERAL" >SDL_SRCALPHA</TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The RGB data is copied from the source. If <TT CLASS="LITERAL" >SDL_SRCCOLORKEY</TT > is set, only the pixels not matching the colorkey value are copied.</P ></TD ></TR ></TBODY ></TABLE ><P ></P ></DIV ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > Note that RGBA->RGBA blits (with SDL_SRCALPHA set) keep the alpha of the destination surface. This means that you cannot compose two arbitrary RGBA surfaces this way and get the result you would expect from "overlaying" them; the destination alpha will work as a mask.</P ><P >Also note that per-pixel and per-surface alpha cannot be combined; the per-pixel alpha is always used if available</P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN2179" ></A ><H2 >Return Value</H2 ><P >This function returns <SPAN CLASS="RETURNVALUE" >0</SPAN >, or <SPAN CLASS="RETURNVALUE" >-1</SPAN > if there was an error.</P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN2184" ></A ><H2 >See Also</H2 ><P ><A HREF="sdlmaprgba.html" ><TT CLASS="FUNCTION" >SDL_MapRGBA</TT ></A >, <A HREF="sdlgetrgba.html" ><TT CLASS="FUNCTION" >SDL_GetRGBA</TT ></A >, <A HREF="sdldisplayformatalpha.html" ><TT CLASS="FUNCTION" >SDL_DisplayFormatAlpha</TT ></A >, <A HREF="sdlblitsurface.html" ><TT CLASS="FUNCTION" >SDL_BlitSurface</TT ></A ></P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="sdlsetcolorkey.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="sdlsetcliprect.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SDL_SetColorKey</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="video.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >SDL_SetClipRect</TD ></TR ></TABLE ></DIV ></BODY ></HTML >