Mercurial > sdl-ios-xcode
view docs/html/sdlsetalpha.html @ 2197:2ff40f30af31
Merged r3261:3262 from branches/SDL-1.2: MMX/YUV with __OPTIMIZE__.
"Mac OS X/x86 won't build the MMX/YUV inline assembly without optimizations
enabled (not enough registers), so for now, we only build it if we see
the __OPTIMIZE__ #define, which GCC provides when you build at -O1 or higher."
author | Ryan C. Gordon <icculus@icculus.org> |
---|---|
date | Sat, 14 Jul 2007 07:28:45 +0000 |
parents | 355632dca928 |
children |
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<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 >