SDL_SetAlpha man page on Aros

Man page or keyword search:  
man Server   366 pages
apropos Keyword Search (all sections)
Output format
Aros logo
[printable version]

SDL_SetAlpha(3)		       SDL API Reference	       SDL_SetAlpha(3)

NAME
       SDL_SetAlpha- Adjust the alpha properties of a surface

SYNOPSIS
       #include "SDL.h"

       int SDL_SetAlpha(SDL_Surface *surface, Uint32 flag, Uint8 alpha);

DESCRIPTION
	      Note:

	      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 consid‐
	      ered   transparent.   This   has	 now	been	inverted:    0
	      (SDL_ALPHA_TRANSPARENT)  is  now	considered transparent and 255
	      (SDL_ALPHA_OPAQUE) is now considered opaque.

       SDL_SetAlpha is used for setting the  per-surface  alpha	 value	and/or
       enabling and disabling alpha blending.

       Thesurface parameter specifies which surface whose alpha attributes you
       wish to adjust. flags is used to specify whether alpha blending	should
       be used (SDL_SRCALPHA) and whether the surface should use RLE accelera‐
       tion for blitting (SDL_RLEACCEL). flags can be an OR'd  combination  of
       these  two  options,  one of these options or 0. If SDL_SRCALPHA is not
       passed as a flag then all alpha information is  ignored	when  blitting
       the surface. The alpha parameter is the per-surface alpha value; a sur‐
       face need not have an alpha channel to use per-surface alpha and	 blit‐
       ting can still be accelerated with SDL_RLEACCEL.

	      Note:

	      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.

       Alpha effects surface blitting in the following ways:

       RGBA->RGB with SDL_SRCALPHA
			   The	source	is alpha-blended with the destination,
			   using the alpha channel.  SDL_SRCCOLORKEY  and  the
			   per-surface alpha are ignored.

       RGBA->RGB without SDL_SRCALPHA
			   The	RGB data is copied from the source. The source
			   alpha channel and the per-surface alpha  value  are
			   ignored.

       RGB->RGBA with SDL_SRCALPHA
			   The	source	is  alpha-blended with the destination
			   using the per-surface alpha value.  If  SDL_SRCCOL‐
			   ORKEY is set, only the pixels not matching the col‐
			   orkey value are copied. The alpha  channel  of  the
			   copied pixels is set to opaque.

       RGB->RGBA without SDL_SRCALPHA
			   The	RGB  data  is  copied  from the source and the
			   alpha value of the copied pixels is set to  opaque.
			   If  SDL_SRCCOLORKEY	is  set,  only	the pixels not
			   matching the colorkey value are copied.

       RGBA->RGBA with SDL_SRCALPHA
			   The source is alpha-blended	with  the  destination
			   using  the  source alpha channel. The alpha channel
			   in  the  destination	 surface  is  left  untouched.
			   SDL_SRCCOLORKEY is ignored.

       RGBA->RGBA without SDL_SRCALPHA
			   The RGBA data is copied to the destination surface.
			   If SDL_SRCCOLORKEY is  set,	only  the  pixels  not
			   matching the colorkey value are copied.

       RGB->RGB with SDL_SRCALPHA
			   The	source	is  alpha-blended with the destination
			   using the per-surface alpha value.  If  SDL_SRCCOL‐
			   ORKEY is set, only the pixels not matching the col‐
			   orkey value are copied.

       RGB->RGB without SDL_SRCALPHA
			   The RGB data is copied from the source. If SDL_SRC‐
			   COLORKEY  is	 set, only the pixels not matching the
			   colorkey value are copied.

	      Note:

	       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.

	      Also note that per-pixel and per-surface alpha  cannot  be  com‐
	      bined; the per-pixel alpha is always used if available

RETURN VALUE
       This function returns 0, or -1 if there was an error.

SEE ALSO
       SDL_MapRGBA, SDL_GetRGBA, SDL_DisplayFormatAlpha, SDL_BlitSurface

SDL			    Tue 11 Sep 2001, 23:01	       SDL_SetAlpha(3)
[top]

List of man pages available for Aros

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net