Mercurial > sdl-ios-xcode
view docs/man3/SDL_SetAlpha.3 @ 4204:976bc19f8f6b SDL-1.2
1.2 Quartz video: Ripped out QuickDraw and QuickTime.
Now we use the software path for YUV, and CoreGraphics for 2D stuff.
There are several other 10.6 fixes in here, too...now we can build a 64-bit
SDL for Snow Leopard!
author | Ryan C. Gordon <icculus@icculus.org> |
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date | Mon, 21 Sep 2009 06:08:23 +0000 |
parents | 4e3b250c950e |
children | 1238da4a7112 |
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.TH "SDL_SetAlpha" "3" "Tue 11 Sep 2001, 23:01" "SDL" "SDL API Reference" .SH "NAME" SDL_SetAlpha \- Adjust the alpha properties of a surface .SH "SYNOPSIS" .PP \fB#include "SDL\&.h" .sp \fBint \fBSDL_SetAlpha\fP\fR(\fBSDL_Surface *surface, Uint32 flag, Uint8 alpha\fR); .SH "DESCRIPTION" .PP .RS \fBNote: .PP 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 (\fBSDL_ALPHA_TRANSPARENT\fP) is now considered transparent and 255 (\fBSDL_ALPHA_OPAQUE\fP) is now considered opaque\&. .RE .PP \fBSDL_SetAlpha\fP is used for setting the per-surface alpha value and/or enabling and disabling alpha blending\&. .PP The\fBsurface\fR parameter specifies which surface whose alpha attributes you wish to adjust\&. \fBflags\fR is used to specify whether alpha blending should be used (\fBSDL_SRCALPHA\fP) and whether the surface should use RLE acceleration for blitting (\fBSDL_RLEACCEL\fP)\&. \fBflags\fR can be an OR\&'d combination of these two options, one of these options or 0\&. If \fBSDL_SRCALPHA\fP is not passed as a flag then all alpha information is ignored when blitting the surface\&. The \fBalpha\fR 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 \fBSDL_RLEACCEL\fP\&. .PP .RS \fBNote: .PP 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\&. .RE .PP Alpha effects surface blitting in the following ways: .TP 20 RGBA->RGB with \fBSDL_SRCALPHA\fP The source is alpha-blended with the destination, using the alpha channel\&. \fBSDL_SRCCOLORKEY\fP and the per-surface alpha are ignored\&. .TP 20 RGBA->RGB without \fBSDL_SRCALPHA\fP The RGB data is copied from the source\&. The source alpha channel and the per-surface alpha value are ignored\&. .TP 20 RGB->RGBA with \fBSDL_SRCALPHA\fP The source is alpha-blended with the destination using the per-surface alpha value\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. The alpha channel of the copied pixels is set to opaque\&. .TP 20 RGB->RGBA without \fBSDL_SRCALPHA\fP The RGB data is copied from the source and the alpha value of the copied pixels is set to opaque\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. .TP 20 RGBA->RGBA with \fBSDL_SRCALPHA\fP The source is alpha-blended with the destination using the source alpha channel\&. The alpha channel in the destination surface is left untouched\&. \fBSDL_SRCCOLORKEY\fP is ignored\&. .TP 20 RGBA->RGBA without \fBSDL_SRCALPHA\fP The RGBA data is copied to the destination surface\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. .TP 20 RGB->RGB with \fBSDL_SRCALPHA\fP The source is alpha-blended with the destination using the per-surface alpha value\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. .TP 20 RGB->RGB without \fBSDL_SRCALPHA\fP The RGB data is copied from the source\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. .PP .RS \fBNote: .PP 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\&. .PP Also note that per-pixel and per-surface alpha cannot be combined; the per-pixel alpha is always used if available .RE .SH "RETURN VALUE" .PP This function returns \fB0\fR, or \fB-1\fR if there was an error\&. .SH "SEE ALSO" .PP \fI\fBSDL_MapRGBA\fP\fR, \fI\fBSDL_GetRGBA\fP\fR, \fI\fBSDL_DisplayFormatAlpha\fP\fR, \fI\fBSDL_BlitSurface\fP\fR ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 23:01