Mercurial > sdl-ios-xcode
view docs/html/sdlpixelformat.html @ 1589:34cca785be57
Xrandr support in the X11 target.
Fixes Bugzilla #109, and as a bonus, Bugzilla #145, too!
author | Ryan C. Gordon <icculus@icculus.org> |
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date | Wed, 22 Mar 2006 11:13:58 +0000 |
parents | e867f327aa54 |
children |
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<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 >