Mercurial > sdl-ios-xcode
comparison docs/man3/SDL_SetAlpha.3 @ 0:74212992fb08
Initial revision
| author | Sam Lantinga <slouken@lokigames.com> |
|---|---|
| date | Thu, 26 Apr 2001 16:45:43 +0000 |
| parents | |
| children | 55f1f1b3e27d |
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| -1:000000000000 | 0:74212992fb08 |
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| 1 .TH "SDL_SetAlpha" "3" "Mon 12 Mar 2001, 01:04" "SDL" "SDL API Reference" | |
| 2 .SH "NAME" | |
| 3 SDL_SetAlpha\- Adjust the alpha properties of a surface | |
| 4 .SH "SYNOPSIS" | |
| 5 .PP | |
| 6 \fB#include "SDL\&.h" | |
| 7 .sp | |
| 8 \fBint \fBSDL_SetAlpha\fP\fR(\fBSDL_Surface *surface, Uint32 flag, Uint8 alpha\fR); | |
| 9 .SH "DESCRIPTION" | |
| 10 .PP | |
| 11 .RS | |
| 12 \fBNote: | |
| 13 .PP | |
| 14 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\&. | |
| 15 .RE | |
| 16 .PP | |
| 17 \fBSDL_SetAlpha\fP is used for setting the per-surface alpha and/or enabling and disabling per-pixel alpha blending\&. | |
| 18 .PP | |
| 19 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\&. Setting the per-surface alpha value to 0 disables per-surface alpha blending\&. | |
| 20 .PP | |
| 21 .RS | |
| 22 \fBNote: | |
| 23 .PP | |
| 24 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\&. | |
| 25 .RE | |
| 26 .PP | |
| 27 Alpha effects surface blitting in the following ways: | |
| 28 .TP 20 | |
| 29 RGBA->RGB with \fBSDL_SRCALPHA\fP | |
| 30 The source is alpha-blended with the destination, using the alpha channel\&. \fBSDL_SRCCOLORKEY\fP and the per-surface alpha are ignored\&. | |
| 31 .TP 20 | |
| 32 RGBA->RGB without \fBSDL_SRCALPHA\fP | |
| 33 The RGB data is copied from the source\&. The source alpha channel and the per-surface alpha value are ignored\&. | |
| 34 .TP 20 | |
| 35 RGB->RGBA with \fBSDL_SRCALPHA\fP | |
| 36 The source is alpha-blended with the destination using the per-surface alpha value\&. If \fBSDL_SRCCOLORKEY\fPliteral> is set, only the pixels not matching the colorkey value are copied\&. | |
| 37 .TP 20 | |
| 38 RGB->RGBA without \fBSDL_SRCALPHA\fP | |
| 39 The RGB data is copied from the source and the destination alpha is zero to opaque\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. | |
| 40 .TP 20 | |
| 41 RGBA->RGBA with \fBSDL_SRCALPHA\fP | |
| 42 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\&. | |
| 43 .TP 20 | |
| 44 RGBA->RGBA without \fBSDL_SRCALPHA\fP | |
| 45 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\&. | |
| 46 .TP 20 | |
| 47 RGB->RGB with \fBSDL_SRCALPHA\fP | |
| 48 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\&. | |
| 49 .TP 20 | |
| 50 RGB->RGB without \fBSDL_SRCALPHA\fP | |
| 51 The RGB data is copied from the source\&. If \fBSDL_SRCCOLORKEY\fP is set, only the pixels not matching the colorkey value are copied\&. | |
| 52 .SH "SEE ALSO" | |
| 53 .PP | |
| 54 \fI\fBSDL_MapRGBA\fP\fR, \fI\fBSDL_GetRGBA\fP\fR, \fI\fBSDL_DisplayFormatAlpha\fP\fR, \fI\fBSDL_BlitSurface\fP\fR | |
| 55 ...\" created by instant / docbook-to-man, Mon 12 Mar 2001, 01:04 |