Mercurial > sdl-ios-xcode
view docs/html/sdlpixelformat.html @ 4134:31c7c57af8a4 SDL-1.2
Updates for building on Windows CE using mingw32ce cross compiler:
http://sourceforge.net/mailarchive/forum.php?thread_name 0703291652.38437.jwalt%40garni.ch&forum_name=cegcc-devel
Hi!
I just managed to compile SDL for Windows CE using the "mingw32ce"
configuration of http://cegcc.sourceforge.net. Test programs work as expected
(except for those using signals -- no POSIX on mingw32ce), and I didn't yet
encounter any problem.
While it was a pain to get everything compiled and running, the changes to
SDL are actually quite small (see attached SDL-ce.diff).
Unfortunately, the win32 headers shipped with cegcc are not 100% correct, and
it feels quite messy to work around them in SDL code, so those headers will
also need to be patched. (Attachment: win32api-ce.diff)
Since I had to apply the libtool patch from the cegcc patch, I have also ad ded
my copy of aclocal.m4 for SDL. I had to modify the cegcc libtool patch to
use "lt_cv_deplibs_check_method=pass_all" for mingw32ce, otherwise libtool
would not recognize the import libraries as valid for dynamic linking.
All these changes should not affect non-WinCE builds, so they could be
included in mainline SDL.
If you need some docs, you can use this description for a cross-compilation
README:
1) get cegcc from http://cegcc.sourceforge.net
2) build and install the "mingw32ce" variant (see cegcc installation docs)
3) patch w32api-headers (if not yet included in cegcc)
4) setup environment (customize the first three lines as you like):
PREFIX=/opt/mingw32ce
TARGET=arm-wince-mingw32ce
BUILD=`uname -m`-pc-linux-gnu
export PATH="$PREFIX/bin:$PREFIX/$TARGET/bin:$PREFIX/local/bin:$PATH"
export CFLAGS="${CFLAGS:- -O2 -g} -I$PREFIX/local/include"
export CPPFLAGS="${CPPFLAGS:- -O2 -g} -I$PREFIX/local/include"
export CXXFLAGS="${CXXFLAGS:- -O2 -g} -I$PREFIX/local/include"
export LDFLAGS="${LDFLAGS:- -O2 -g} -L$PREFIX/local/lib"
export HOST_CC="gcc"
export CC="$PREFIX/bin/$TARGET-gcc"
export CXX="$PREFIX/bin/$TARGET-g++"
export LD="$PREFIX/bin/$TARGET-ld"
export AS="$PREFIX/bin/$TARGET-as"
export AR="$PREFIX/bin/$TARGET-ar"
export RANLIB="$PREFIX/bin/$TARGET-ranlib"
export CONFIG_SHELL="/bin/sh"
5) build and install
./configure --target=$TARGET --host=$TARGET --build=$BUILD
make
make install
6) use (4) and (5) for any SDL-using software you want to cross-compile
7) copy $PREFIX/local/bin/SDL-1-2-0.dll into your executable directory on the WinCE machine
| author | Sam Lantinga <slouken@libsdl.org> |
|---|---|
| date | Thu, 03 Jan 2008 06:19:07 +0000 |
| parents | e867f327aa54 |
| children |
line wrap: on
line source
<HTML ><HEAD ><TITLE >SDL_PixelFormat</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="SDL Library Documentation" HREF="index.html"><LINK REL="UP" TITLE="Video" HREF="video.html"><LINK REL="PREVIOUS" TITLE="SDL_Palette" HREF="sdlpalette.html"><LINK REL="NEXT" TITLE="SDL_Surface" HREF="sdlsurface.html"></HEAD ><BODY CLASS="REFENTRY" BGCOLOR="#FFF8DC" TEXT="#000000" LINK="#0000ee" VLINK="#551a8b" ALINK="#ff0000" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >SDL Library Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="sdlpalette.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="sdlsurface.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="SDLPIXELFORMAT" ></A >SDL_PixelFormat</H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN3178" ></A ><H2 >Name</H2 >SDL_PixelFormat -- Stores surface format information</DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN3181" ></A ><H2 >Structure Definition</H2 ><PRE CLASS="PROGRAMLISTING" >typedef struct SDL_PixelFormat { SDL_Palette *palette; Uint8 BitsPerPixel; Uint8 BytesPerPixel; Uint8 Rloss, Gloss, Bloss, Aloss; Uint8 Rshift, Gshift, Bshift, Ashift; Uint32 Rmask, Gmask, Bmask, Amask; Uint32 colorkey; Uint8 alpha; } SDL_PixelFormat;</PRE ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN3184" ></A ><H2 >Structure Data</H2 ><DIV CLASS="INFORMALTABLE" ><A NAME="AEN3186" ></A ><P ></P ><TABLE BORDER="0" CLASS="CALSTABLE" ><TBODY ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >palette</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >Pointer to the <A HREF="sdlpalette.html" >palette</A >, or <TT CLASS="LITERAL" >NULL</TT > if the <TT CLASS="STRUCTFIELD" ><I >BitsPerPixel</I ></TT >>8</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >BitsPerPixel</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32.</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >BytesPerPixel</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >The number of bytes used to represent each pixel in a surface. Usually one to four.</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >[RGBA]mask</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >Binary mask used to retrieve individual color values</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >[RGBA]loss</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >Precision loss of each color component (2<SUP >[RGBA]loss</SUP >)</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >[RGBA]shift</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >Binary left shift of each color component in the pixel value</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >colorkey</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >Pixel value of transparent pixels</TD ></TR ><TR ><TD ALIGN="LEFT" VALIGN="TOP" ><TT CLASS="STRUCTFIELD" ><I >alpha</I ></TT ></TD ><TD ALIGN="LEFT" VALIGN="TOP" >Overall surface alpha value</TD ></TR ></TBODY ></TABLE ><P ></P ></DIV ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN3225" ></A ><H2 >Description</H2 ><P >A <SPAN CLASS="STRUCTNAME" >SDL_PixelFormat</SPAN > describes the format of the pixel data stored at the <TT CLASS="STRUCTFIELD" ><I >pixels</I ></TT > field of a <A HREF="sdlsurface.html" ><SPAN CLASS="STRUCTNAME" >SDL_Surface</SPAN ></A >. Every surface stores a <SPAN CLASS="STRUCTNAME" >SDL_PixelFormat</SPAN > in the <TT CLASS="STRUCTFIELD" ><I >format</I ></TT > field.</P ><P >If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential.</P ><P >8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 <TT CLASS="STRUCTFIELD" ><I >BitsPerPixel</I ></TT > and 1 <TT CLASS="STRUCTFIELD" ><I >BytesPerPixel</I ></TT >. Since <TT CLASS="STRUCTFIELD" ><I >BytesPerPixel</I ></TT > is 1, all pixels are represented by a Uint8 which contains an index into <TT CLASS="STRUCTFIELD" ><I >palette</I ></TT >-><TT CLASS="STRUCTFIELD" ><I >colors</I ></TT >. So, to determine the color of a pixel in a 8-bit surface: we read the color index from <SPAN CLASS="STRUCTNAME" >surface</SPAN >-><TT CLASS="STRUCTFIELD" ><I >pixels</I ></TT > and we use that index to read the <A HREF="sdlcolor.html" ><SPAN CLASS="STRUCTNAME" >SDL_Color</SPAN ></A > structure from <SPAN CLASS="STRUCTNAME" >surface</SPAN >-><TT CLASS="STRUCTFIELD" ><I >format</I ></TT >-><TT CLASS="STRUCTFIELD" ><I >palette</I ></TT >-><TT CLASS="STRUCTFIELD" ><I >colors</I ></TT >. Like so: <PRE CLASS="PROGRAMLISTING" >SDL_Surface *surface; SDL_PixelFormat *fmt; SDL_Color *color; Uint8 index; . . /* Create surface */ . . fmt=surface->format; /* Check the bitdepth of the surface */ if(fmt->BitsPerPixel!=8){ fprintf(stderr, "Not an 8-bit surface.\n"); return(-1); } /* Lock the surface */ SDL_LockSurface(surface); /* Get the topleft pixel */ index=*(Uint8 *)surface->pixels; color=fmt->palette->colors[index]; /* Unlock the surface */ SDL_UnlockSurface(surface); printf("Pixel Color-> Red: %d, Green: %d, Blue: %d. Index: %d\n", color->r, color->g, color->b, index); . .</PRE ></P ><P >Pixel formats above 8-bit are an entirely different experience. They are considered to be "TrueColor" formats and the color information is stored in the pixels themselves, not in a palette. The mask, shift and loss fields tell us how the color information is encoded. The mask fields allow us to isolate each color component, the shift fields tell us the number of bits to the right of each component in the pixel value and the loss fields tell us the number of bits lost from each component when packing 8-bit color component in a pixel. <PRE CLASS="PROGRAMLISTING" >/* Extracting color components from a 32-bit color value */ SDL_PixelFormat *fmt; SDL_Surface *surface; Uint32 temp, pixel; Uint8 red, green, blue, alpha; . . . fmt=surface->format; SDL_LockSurface(surface); pixel=*((Uint32*)surface->pixels); SDL_UnlockSurface(surface); /* Get Red component */ temp=pixel&fmt->Rmask; /* Isolate red component */ temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */ temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */ red=(Uint8)temp; /* Get Green component */ temp=pixel&fmt->Gmask; /* Isolate green component */ temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */ temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */ green=(Uint8)temp; /* Get Blue component */ temp=pixel&fmt->Bmask; /* Isolate blue component */ temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */ temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */ blue=(Uint8)temp; /* Get Alpha component */ temp=pixel&fmt->Amask; /* Isolate alpha component */ temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */ temp=temp<<fmt->Aloss; /* Expand to a full 8-bit number */ alpha=(Uint8)temp; printf("Pixel Color -> R: %d, G: %d, B: %d, A: %d\n", red, green, blue, alpha); . . .</PRE ></P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN3252" ></A ><H2 >See Also</H2 ><P ><A HREF="sdlsurface.html" ><SPAN CLASS="STRUCTNAME" >SDL_Surface</SPAN ></A >, <A HREF="sdlmaprgb.html" ><TT CLASS="FUNCTION" >SDL_MapRGB</TT ></A ></P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="sdlpalette.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="sdlsurface.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SDL_Palette</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="video.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >SDL_Surface</TD ></TR ></TABLE ></DIV ></BODY ></HTML >