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view docs/man3/SDL_GL_SetAttribute.3 @ 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 | 546f7c1eb755 |
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.TH "SDL_GL_SetAttribute" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference" .SH "NAME" SDL_GL_SetAttribute\- Set a special SDL/OpenGL attribute .SH "SYNOPSIS" .PP \fB#include "SDL\&.h" .sp \fBint \fBSDL_GL_SetAttribute\fP\fR(\fBSDL_GLattr attr, int value\fR); .SH "DESCRIPTION" .PP Sets the OpenGL \fIattribute\fR \fBattr\fR to \fBvalue\fR\&. The attributes you set don\&'t take effect until after a call to \fI\fBSDL_SetVideoMode\fP\fR\&. You should use \fI\fBSDL_GL_GetAttribute\fP\fR to check the values after a \fBSDL_SetVideoMode\fP call\&. .SH "RETURN VALUE" .PP Returns \fB0\fR on success, or \fB-1\fR on error\&. .SH "EXAMPLE" .PP .nf \f(CWSDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 ); SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 ); SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 ); SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 ); SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 ); if ( (screen=SDL_SetVideoMode( 640, 480, 16, SDL_OPENGL )) == NULL ) { fprintf(stderr, "Couldn\&'t set GL mode: %s ", SDL_GetError()); SDL_Quit(); return; }\fR .fi .PP .PP .RS \fBNote: .PP The \fBSDL_DOUBLEBUF\fP flag is not required to enable double buffering when setting an OpenGL video mode\&. Double buffering is enabled or disabled using the SDL_GL_DOUBLEBUFFER attribute\&. .RE .SH "SEE ALSO" .PP \fI\fBSDL_GL_GetAttribute\fP\fR, \fIGL Attributes\fR ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01