forked from KolibriOS/kolibrios
520 lines
8.1 KiB
HTML
520 lines
8.1 KiB
HTML
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<HTML
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><HEAD
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><TITLE
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>SDL_PixelFormat</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.64
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"><LINK
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REL="HOME"
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TITLE="SDL Library Documentation"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Video"
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HREF="video.html"><LINK
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REL="PREVIOUS"
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TITLE="SDL_Palette"
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HREF="sdlpalette.html"><LINK
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REL="NEXT"
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TITLE="SDL_Surface"
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HREF="sdlsurface.html"></HEAD
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><BODY
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CLASS="REFENTRY"
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BGCOLOR="#FFF8DC"
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TEXT="#000000"
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LINK="#0000ee"
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VLINK="#551a8b"
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ALINK="#ff0000"
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><DIV
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CLASS="NAVHEADER"
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WIDTH="100%"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>SDL Library Documentation</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="sdlpalette.html"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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></TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="sdlsurface.html"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="SDLPIXELFORMAT"
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>SDL_PixelFormat</A
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></H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN2756"
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></A
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><H2
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>Name</H2
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>SDL_PixelFormat -- Stores surface format information</DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN2759"
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></A
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><H2
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>Structure Definition</H2
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><PRE
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CLASS="PROGRAMLISTING"
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>typedef struct{
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SDL_Palette *palette;
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Uint8 BitsPerPixel;
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Uint8 BytesPerPixel;
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Uint32 Rmask, Gmask, Bmask, Amask;
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Uint8 Rshift, Gshift, Bshift, Ashift;
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Uint8 Rloss, Gloss, Bloss, Aloss;
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Uint32 colorkey;
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Uint8 alpha;
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} SDL_PixelFormat;</PRE
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN2762"
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></A
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><H2
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>Structure Data</H2
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><DIV
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CLASS="INFORMALTABLE"
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><A
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NAME="AEN2764"
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></A
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><P
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></P
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><TABLE
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BORDER="0"
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CLASS="CALSTABLE"
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><TBODY
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>palette</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Pointer to the <A
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HREF="sdlpalette.html"
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>palette</A
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>, or <TT
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CLASS="LITERAL"
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>NULL</TT
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> if the <TT
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CLASS="STRUCTFIELD"
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><I
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>BitsPerPixel</I
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></TT
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>>8</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>BitsPerPixel</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32.</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>BytesPerPixel</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>The number of bytes used to represent each pixel in a surface. Usually one to four.</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>[RGBA]mask</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Binary mask used to retrieve individual color values</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>[RGBA]loss</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Precision loss of each color component (2<SUP
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>[RGBA]loss</SUP
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>)</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>[RGBA]shift</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Binary left shift of each color component in the pixel value</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>colorkey</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Pixel value of transparent pixels</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>alpha</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Overall surface alpha value</TD
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></TR
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></TBODY
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></TABLE
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><P
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></P
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></DIV
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN2803"
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></A
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><H2
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>Description</H2
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><P
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>A <SPAN
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CLASS="STRUCTNAME"
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>SDL_PixelFormat</SPAN
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> describes the format of the pixel data stored at the <TT
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CLASS="STRUCTFIELD"
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><I
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>pixels</I
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></TT
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> field of a <A
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HREF="sdlsurface.html"
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><SPAN
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CLASS="STRUCTNAME"
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>SDL_Surface</SPAN
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></A
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>. Every surface stores a <SPAN
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CLASS="STRUCTNAME"
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>SDL_PixelFormat</SPAN
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> in the <TT
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CLASS="STRUCTFIELD"
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><I
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>format</I
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></TT
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> field.</P
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><P
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>If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential.</P
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><P
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>8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 <TT
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CLASS="STRUCTFIELD"
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><I
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>BitsPerPixel</I
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></TT
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> and 1 <TT
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CLASS="STRUCTFIELD"
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><I
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>BytesPerPixel</I
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></TT
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>. Since <TT
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CLASS="STRUCTFIELD"
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><I
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>BytesPerPixel</I
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></TT
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> is 1, all pixels are represented by a Uint8 which contains an index into <TT
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CLASS="STRUCTFIELD"
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><I
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>palette</I
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></TT
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>colors</I
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></TT
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>. So, to determine the color of a pixel in a 8-bit surface: we read the color index from <SPAN
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CLASS="STRUCTNAME"
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>surface</SPAN
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>pixels</I
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></TT
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> and we use that index to read the <A
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HREF="sdlcolor.html"
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><SPAN
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CLASS="STRUCTNAME"
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>SDL_Color</SPAN
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></A
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> structure from <SPAN
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CLASS="STRUCTNAME"
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>surface</SPAN
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>format</I
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></TT
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>palette</I
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></TT
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>colors</I
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></TT
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>. Like so:
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<PRE
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CLASS="PROGRAMLISTING"
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>SDL_Surface *surface;
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SDL_PixelFormat *fmt;
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SDL_Color *color;
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Uint8 index;
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.
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.
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/* Create surface */
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.
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.
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fmt=surface->format;
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/* Check the bitdepth of the surface */
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if(fmt->BitsPerPixel!=8){
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fprintf(stderr, "Not an 8-bit surface.\n");
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return(-1);
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}
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/* Lock the surface */
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SDL_LockSurface(surface);
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/* Get the topleft pixel */
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index=*(Uint8 *)surface->pixels;
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color=fmt->palette->colors[index];
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/* Unlock the surface */
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SDL_UnlockSurface(surface);
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printf("Pixel Color-> Red: %d, Green: %d, Blue: %d. Index: %d\n",
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color->r, color->g, color->b, index);
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.
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.</PRE
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></P
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><P
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>Pixel formats above 8-bit are an entirely different experience. They are
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considered to be "TrueColor" formats and the color information is stored in the
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pixels themselves, not in a palette. The mask, shift and loss fields tell us
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how the color information is encoded. The mask fields allow us to isolate each
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color component, the shift fields tell us the number of bits to the right of
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each component in the pixel value and the loss fields tell us the number of
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bits lost from each component when packing 8-bit color component in a pixel.
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<PRE
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CLASS="PROGRAMLISTING"
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>/* Extracting color components from a 32-bit color value */
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SDL_PixelFormat *fmt;
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SDL_Surface *surface;
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Uint32 temp, pixel;
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Uint8 red, green, blue, alpha;
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.
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.
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.
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fmt=surface->format;
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SDL_LockSurface(surface);
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pixel=*((Uint32*)surface->pixels);
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SDL_UnlockSurface(surface);
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/* Get Red component */
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temp=pixel&fmt->Rmask; /* Isolate red component */
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temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */
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temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */
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red=(Uint8)temp;
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/* Get Green component */
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temp=pixel&fmt->Gmask; /* Isolate green component */
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temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */
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temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */
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green=(Uint8)temp;
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/* Get Blue component */
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temp=pixel&fmt->Bmask; /* Isolate blue component */
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temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */
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temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */
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blue=(Uint8)temp;
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/* 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="AEN2830"
|
||
|
|
></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
|
||
|
|
WIDTH="100%"
|
||
|
|
BORDER="0"
|
||
|
|
CELLPADDING="0"
|
||
|
|
CELLSPACING="0"
|
||
|
|
><TR
|
||
|
|
><TD
|
||
|
|
WIDTH="33%"
|
||
|
|
ALIGN="left"
|
||
|
|
VALIGN="top"
|
||
|
|
><A
|
||
|
|
HREF="sdlpalette.html"
|
||
|
|
>Prev</A
|
||
|
|
></TD
|
||
|
|
><TD
|
||
|
|
WIDTH="34%"
|
||
|
|
ALIGN="center"
|
||
|
|
VALIGN="top"
|
||
|
|
><A
|
||
|
|
HREF="index.html"
|
||
|
|
>Home</A
|
||
|
|
></TD
|
||
|
|
><TD
|
||
|
|
WIDTH="33%"
|
||
|
|
ALIGN="right"
|
||
|
|
VALIGN="top"
|
||
|
|
><A
|
||
|
|
HREF="sdlsurface.html"
|
||
|
|
>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"
|
||
|
|
>Up</A
|
||
|
|
></TD
|
||
|
|
><TD
|
||
|
|
WIDTH="33%"
|
||
|
|
ALIGN="right"
|
||
|
|
VALIGN="top"
|
||
|
|
>SDL_Surface</TD
|
||
|
|
></TR
|
||
|
|
></TABLE
|
||
|
|
></DIV
|
||
|
|
></BODY
|
||
|
|
></HTML
|
||
|
|
>
|