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Date: Fri, 19 Dec 2008 20:17:35 +0100 From: Couriersud Subject: Re: Aw: Experience using SDL1.3 in sdlmame/Proposal for api additions > For consistency you'd probably want: > SDL_SetRenderDrawColor(Uint8 r, Uint8 g, Uint8 b, Uint8 a); > SDL_SetRenderDrawBlendMode(SDL_BlendMode blendMode); > SDL_RenderLine(int x1, int y1, int x2, int y2); > SDL_RenderFill(SDL_Rect *rect); > > You probably also want to add API functions query the current state. > I have implemented the above api for the opengl, x11, directfb and software renderers. I have also renamed *TEXTUREBLENDMODE* constants to BLENDMODE*. The unix build compiles. The windows renderer still needs to be updated, but I have no windows development machine at hand. Have a look at the x11 renderer for a sample. Vector games now run at 90% both on opengl and directfb in comparison to sdlmame's own opengl renderer. The same applies to raster games. The diff also includes a) Changed XDrawRect to XFillRect in x11 renderer b) A number of changes to fix blending and modulation issues in the directfb renderer.
author Sam Lantinga <slouken@libsdl.org>
date Sat, 20 Dec 2008 12:00:00 +0000
parents 355632dca928
children
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<HTML
><HEAD
><TITLE
>SDL_SetAlpha</TITLE
><META
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><HR
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><H1
><A
NAME="SDLSETALPHA"
></A
>SDL_SetAlpha</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN2096"
></A
><H2
>Name</H2
>SDL_SetAlpha&nbsp;--&nbsp;Adjust the alpha properties of a surface</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN2099"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN2100"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include "SDL.h"</PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int <B
CLASS="FSFUNC"
>SDL_SetAlpha</B
></CODE
>(SDL_Surface *surface, Uint32 flag, Uint8 alpha);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN2106"
></A
><H2
>Description</H2
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>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 (<TT
CLASS="LITERAL"
>SDL_ALPHA_TRANSPARENT</TT
>) is now considered transparent and 255 (<TT
CLASS="LITERAL"
>SDL_ALPHA_OPAQUE</TT
>) is now considered opaque.</P
></BLOCKQUOTE
></DIV
><P
><TT
CLASS="FUNCTION"
>SDL_SetAlpha</TT
> is used for setting the per-surface alpha
value and/or enabling and disabling alpha blending.</P
><P
>The<TT
CLASS="PARAMETER"
><I
>surface</I
></TT
> parameter specifies which surface whose alpha
attributes you wish to adjust. <TT
CLASS="PARAMETER"
><I
>flags</I
></TT
> is used to specify
whether alpha blending should be used (<TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
>) and
whether the surface should use RLE acceleration for blitting
(<TT
CLASS="LITERAL"
>SDL_RLEACCEL</TT
>). <TT
CLASS="PARAMETER"
><I
>flags</I
></TT
> can be an OR'd
combination of these two options, one of these options or 0. If
<TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
> is not passed as a flag then all alpha
information is ignored when blitting the surface. The
<TT
CLASS="PARAMETER"
><I
>alpha</I
></TT
> 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 <TT
CLASS="LITERAL"
>SDL_RLEACCEL</TT
>.</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>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.</P
></BLOCKQUOTE
></DIV
><P
>Alpha effects surface blitting in the following ways:</P
><DIV
CLASS="INFORMALTABLE"
><A
NAME="AEN2126"
></A
><P
></P
><TABLE
BORDER="0"
CLASS="CALSTABLE"
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGBA-&#62;RGB with <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The source is alpha-blended with the destination, using the alpha channel. <TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
> and the per-surface alpha are ignored.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGBA-&#62;RGB without <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The RGB data is copied from the source. The source alpha channel and the per-surface alpha value are ignored.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGB-&#62;RGBA with <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The source is alpha-blended with the destination using the per-surface alpha
value. If <TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
> is set, only the pixels not
matching the colorkey value are copied. The alpha channel of the copied pixels
is set to opaque.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGB-&#62;RGBA without <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The RGB data is copied from the source and the alpha value of the copied pixels
is set to opaque. If <TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
> is set, only the pixels
not matching the colorkey value are copied. </P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGBA-&#62;RGBA with <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The source is alpha-blended with the destination using the source alpha
channel. The alpha channel in the destination surface is left untouched.
<TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
> is ignored.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGBA-&#62;RGBA without <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The RGBA data is copied to the destination surface. If <TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
> is set, only the pixels not matching the colorkey value are copied.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGB-&#62;RGB with <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The source is alpha-blended with the destination using the per-surface alpha value. If <TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
> is set, only the pixels not matching the colorkey value are copied.</P
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>RGB-&#62;RGB without <TT
CLASS="LITERAL"
>SDL_SRCALPHA</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The RGB data is copied from the source. If <TT
CLASS="LITERAL"
>SDL_SRCCOLORKEY</TT
> is set, only the pixels not matching the colorkey value are copied.</P
></TD
></TR
></TBODY
></TABLE
><P
></P
></DIV
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Note that RGBA-&#62;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.</P
><P
>Also note that per-pixel and per-surface alpha cannot be combined;
the per-pixel alpha is always used if available</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN2179"
></A
><H2
>Return Value</H2
><P
>This function returns <SPAN
CLASS="RETURNVALUE"
>0</SPAN
>, or
<SPAN
CLASS="RETURNVALUE"
>-1</SPAN
> if there was an error.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN2184"
></A
><H2
>See Also</H2
><P
><A
HREF="sdlmaprgba.html"
><TT
CLASS="FUNCTION"
>SDL_MapRGBA</TT
></A
>,
<A
HREF="sdlgetrgba.html"
><TT
CLASS="FUNCTION"
>SDL_GetRGBA</TT
></A
>,
<A
HREF="sdldisplayformatalpha.html"
><TT
CLASS="FUNCTION"
>SDL_DisplayFormatAlpha</TT
></A
>,
<A
HREF="sdlblitsurface.html"
><TT
CLASS="FUNCTION"
>SDL_BlitSurface</TT
></A
></P
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