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Date: Thu, 17 Jun 2004 11:38:51 -0700 (PDT) From: Eric Wing <ewing2121@yahoo.com> Subject: New OS X patch (was Re: [SDL] Bug with inverted mouse coordinates in I have a new patch for OS X I would like to submit. First, it appears no further action has been taken on my fix from Apple on the OpenGL windowed mode mouse inversion problem. The fix would reunify the code, and no longer require case checking for which version of the OS you are running. This is probably a good fix because the behavior with the old code could change again with future versions of the OS, so those fixes are included in this new patch. But in addition, when I was at Apple, I asked them about the ability to distinguish between the modifier keys on the left and right sides of the keyboard (e.g. Left Shift, Right Shift, Left/Right Alt, L/R Cmd, L/R Ctrl). They told me that starting with Panther, the OS began supporting this feature. This has always been a source of annoyance for me when bringing a program that comes from Windows or Linux to OS X when the keybindings happened to need distinguishable left-side and right-side keys. So the rest of the patch I am submitting contains new code to support this feature on Panther (and presumably later versions of the OS). So after removing the OS version checks for the mouse inversion problem, I reused the OS version checks to activate the Left/Right detection of modifier keys. If you are running Panther (or above), the new code will attempt to distinguish between sides. For the older OS's, the code path reverts to the original code. I've tested with Panther on a G4 Cube, G5 dual processor, and Powerbook Rev C. The Cube and G5 keyboards demonstrated the ability to distinguish between sides. The Powerbook seems to only have left-side keys, but the patch was still able to handle it by producing the same results as before the patch. I also wanted to test a non-Apple keyboard. Unfortunately, I don't have any PC USB keyboards. However, I was able to borrow a Sun Microsystems USB keyboard, so I tried that out on the G5, and I got the correct behavior for left and right sides. I'm expecting that if it worked with a Sun keyboard, most other keyboards should work with no problems.
author Sam Lantinga <slouken@libsdl.org>
date Fri, 20 Aug 2004 22:35:23 +0000
parents 355632dca928
children e867f327aa54
line wrap: on
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<HTML
><HEAD
><TITLE
>SDL_PixelFormat</TITLE
><META
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><H1
><A
NAME="SDLPIXELFORMAT"
></A
>SDL_PixelFormat</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN3178"
></A
><H2
>Name</H2
>SDL_PixelFormat&nbsp;--&nbsp;Stores surface format information</DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN3181"
></A
><H2
>Structure Definition</H2
><PRE
CLASS="PROGRAMLISTING"
>typedef struct{
  SDL_Palette *palette;
  Uint8  BitsPerPixel;
  Uint8  BytesPerPixel;
  Uint32 Rmask, Gmask, Bmask, Amask;
  Uint8  Rshift, Gshift, Bshift, Ashift;
  Uint8  Rloss, Gloss, Bloss, Aloss;
  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
>&#62;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
>-&#62;<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
>-&#62;<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
>-&#62;<TT
CLASS="STRUCTFIELD"
><I
>format</I
></TT
>-&#62;<TT
CLASS="STRUCTFIELD"
><I
>palette</I
></TT
>-&#62;<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-&#62;format;

/* Check the bitdepth of the surface */
if(fmt-&#62;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-&#62;pixels;
color=fmt-&#62;palette-&#62;colors[index];

/* Unlock the surface */
SDL_UnlockSurface(surface);
printf("Pixel Color-&#62; Red: %d, Green: %d, Blue: %d. Index: %d\n",
          color-&#62;r, color-&#62;g, color-&#62;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-&#62;format;
SDL_LockSurface(surface);
pixel=*((Uint32*)surface-&#62;pixels);
SDL_UnlockSurface(surface);

/* Get Red component */
temp=pixel&#38;fmt-&#62;Rmask; /* Isolate red component */
temp=temp&#62;&#62;fmt-&#62;Rshift;/* Shift it down to 8-bit */
temp=temp&#60;&#60;fmt-&#62;Rloss; /* Expand to a full 8-bit number */
red=(Uint8)temp;

/* Get Green component */
temp=pixel&#38;fmt-&#62;Gmask; /* Isolate green component */
temp=temp&#62;&#62;fmt-&#62;Gshift;/* Shift it down to 8-bit */
temp=temp&#60;&#60;fmt-&#62;Gloss; /* Expand to a full 8-bit number */
green=(Uint8)temp;

/* Get Blue component */
temp=pixel&#38;fmt-&#62;Bmask; /* Isolate blue component */
temp=temp&#62;&#62;fmt-&#62;Bshift;/* Shift it down to 8-bit */
temp=temp&#60;&#60;fmt-&#62;Bloss; /* Expand to a full 8-bit number */
blue=(Uint8)temp;

/* Get Alpha component */
temp=pixel&#38;fmt-&#62;Amask; /* Isolate alpha component */
temp=temp&#62;&#62;fmt-&#62;Ashift;/* Shift it down to 8-bit */
temp=temp&#60;&#60;fmt-&#62;Aloss; /* Expand to a full 8-bit number */
alpha=(Uint8)temp;

printf("Pixel Color -&#62; R: %d,  G: %d,  B: %d,  A: %d\n", red, green, blue, alpha);
.
.
.</PRE
></P
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><A
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></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
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