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view docs/html/sdlflip.html @ 688:c0522010bb6d
Date: Tue, 12 Aug 2003 14:26:19 +0200 (MEST)
From: "Mattias Engdeg?rd"
Subject: bug in SDL_GetRGB/GetRGBA
There's an embarrassing bug in GetRGB/GetRGBA which apparently has been there
for years. It incorrectly converts colours with < 8 bits/channel.
It came to my attention today in #sdl.
What it does now is (for each channel):
rv = (pixel & fmt->Rmask) >> fmt->Rshift;
*r = (rv << fmt->Rloss) + (rv >> (8 - fmt->Rloss));
which is wrong; the last line should be
*r = (rv << fmt->Rloss) + (rv >> (8 - (fmt->Rloss << 1)));
author | Sam Lantinga <slouken@libsdl.org> |
---|---|
date | Tue, 12 Aug 2003 15:17:20 +0000 |
parents | e5bc29de3f0a |
children | 355632dca928 |
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<HTML ><HEAD ><TITLE >SDL_Flip</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.64 "><LINK REL="HOME" TITLE="SDL Library Documentation" HREF="index.html"><LINK REL="UP" TITLE="Video" HREF="video.html"><LINK REL="PREVIOUS" TITLE="SDL_UpdateRects" HREF="sdlupdaterects.html"><LINK REL="NEXT" TITLE="SDL_SetColors" HREF="sdlsetcolors.html"></HEAD ><BODY CLASS="REFENTRY" BGCOLOR="#FFF8DC" TEXT="#000000" LINK="#0000ee" VLINK="#551a8b" ALINK="#ff0000" ><DIV CLASS="NAVHEADER" ><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="sdlupdaterects.html" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="sdlsetcolors.html" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="SDLFLIP" >SDL_Flip</A ></H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN1042" ></A ><H2 >Name</H2 >SDL_Flip -- Swaps screen buffers</DIV ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN1045" ></A ><H2 >Synopsis</H2 ><DIV CLASS="FUNCSYNOPSIS" ><A NAME="AEN1046" ></A ><P ></P ><PRE CLASS="FUNCSYNOPSISINFO" >#include "SDL.h"</PRE ><P ><CODE ><CODE CLASS="FUNCDEF" >int <B CLASS="FSFUNC" >SDL_Flip</B ></CODE >(SDL_Surface *screen);</CODE ></P ><P ></P ></DIV ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN1052" ></A ><H2 >Description</H2 ><P >On hardware that supports double-buffering, this function sets up a flip and returns. The hardware will wait for vertical retrace, and then swap video buffers before the next video surface blit or lock will return. On hardware that doesn't support double-buffering, this is equivalent to calling <A HREF="sdlupdaterect.html" >SDL_UpdateRect</A ><TT CLASS="PARAMETER" ><I >(screen, 0, 0, 0, 0)</I ></TT ></P ><P >The <TT CLASS="LITERAL" >SDL_DOUBLEBUF</TT > flag must have been passed to <A HREF="sdlsetvideomode.html" >SDL_SetVideoMode</A >, when setting the video mode for this function to perform hardware flipping.</P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN1060" ></A ><H2 >Return Value</H2 ><P >This function returns <SPAN CLASS="RETURNVALUE" >0</SPAN > if successful, or <SPAN CLASS="RETURNVALUE" >-1</SPAN > if there was an error.</P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN1065" ></A ><H2 >See Also</H2 ><P ><A HREF="sdlsetvideomode.html" ><TT CLASS="FUNCTION" >SDL_SetVideoMode</TT ></A >, <A HREF="sdlupdaterect.html" ><TT CLASS="FUNCTION" >SDL_UpdateRect</TT ></A >, <A HREF="sdlsurface.html" ><SPAN CLASS="STRUCTNAME" >SDL_Surface</SPAN ></A ></P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="sdlupdaterects.html" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="sdlsetcolors.html" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SDL_UpdateRects</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="video.html" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >SDL_SetColors</TD ></TR ></TABLE ></DIV ></BODY ></HTML >