From: "Mark Q" <cragwolf@delete.iprimus.com.au.this>
Newsgroups: borland.public.delphi.graphics
Subject: Interesting effect with XOR
Date: Sun, 18 Nov 2001 23:36:35 +1100
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Hello,

I just thought some of you might find this "special effect" vaguely
interesting. It reminds me of a fractal I once saw. Create a new
application, add a button to the form, and add the following code for the
button's onclock event:

var
  bih : TBitmapInfo;
  i, j : Byte;
  ptrBits, ptrTemp : Pointer;
begin
  // Initialise BITMAPINFO structure
  ZeroMemory(@bih, SizeOf(bih));
  with bih.bmiHeader do begin
    biSize := SizeOf(TBitmapInfoHeader);
    biWidth := 256;
    biHeight := 256;
    biPlanes := 1;
    biBitCount := 24;
    biSizeImage := 256*256*3;
  end; {with}
  // Allocate memory for pixel data
  ptrBits := GlobalAllocPtr(GMEM_FIXED or GMEM_ZEROINIT, 256*256*3);
  try
    ptrTemp := ptrBits;
    // Manipulate pixels using XOR operator
    for j := 0 to 255 do begin
      for i := 0 to 255 do begin
        PByte(ptrTemp)^ := i xor j;  // Blue component
        Inc(PByte(ptrTemp));
        PByte(ptrTemp)^ := i xor j;  // Green component
        Inc(PByte(ptrTemp));
        PByte(ptrTemp)^ := i xor j;  // Red component
        Inc(PByte(ptrTemp));
      end; {for}
    end; {for}
    // Draw to screen
    StretchDIBits(Canvas.Handle, 0, 255, 256, -256, 0, 0, 256, 256,
                  ptrBits, bih, DIB_RGB_COLORS, SRCCOPY);
  finally
    GlobalFreePtr(ptrBits);
  end; {try}
end;

// tested for Delphi 4
// Mark Q