旋转位图

Here's code to rotate a bitmap 90 degrees

From: Dave Shapiro <daves@cyber-fx.com>
Counterclockwise, that is. This rotates a 640x480 24-bit bitmap 90 degrees in about 2/10 of sec on my P133 (4MB video card, 128MB RAM). It works for Delphi 2, and should work for 1 and 3, too.

One thing: This does not work for bitmaps that aren't an integral number of colors per pixel. If that's the case, you'll have to do some bit twiddling. I'm working on that part right now (I need it too), but it'll be a few days. Anyways, suggestions, comments, etc., always welcome.

Special thanks to David Ullrich (ooh, I hope I spelled that correctly) for pointing out the non-published-but-public-anyway SaveToStream method for the TBitmap class.

Advance apologies for any formatting problems. Netscape's editor is so ridiculously crippled that I can't accomplish anything (give me rtin and vim any day).

--------------------------------------------------------------------------------

procedure RotateBitmap90Degrees(ABitmap: TBitmap);

const
  BITMAP_HEADER_SIZE = SizeOf(TBitmapFileHeader) +
SizeOf(TBitmapInfoHeader);

var
  { Things that end in R are for the rotated image. }
  PbmpInfoR: PBitmapInfoHeader;
  bmpBuffer, bmpBufferR: PByte;
  MemoryStream, MemoryStreamR: TMemoryStream;
  PbmpBuffer, PbmpBufferR: PByte;
  PbmpBufferRFirstScanLine, PbmpBufferColumnZero: PByte;
  BytesPerPixel, BytesPerScanLine, BytesPerScanLineR: Integer;
  X, Y, T: Integer;

begin
  {
    Don't *ever* call GetDIBSizes! It screws up your bitmap.
    I'll be posting about that shortly.
  }

  MemoryStream := TMemoryStream.Create;

  {
   To do: Put in a SetSize, which will eliminate any reallocation
   overhead.
  }

  ABitmap.SaveToStream(MemoryStream);

  {
   Don't need you anymore. We'll make a new one when the time comes.
  }
  ABitmap.Free;

  bmpBuffer := MemoryStream.Memory;

  { Set PbmpInfoR to point to the source bitmap's info header. }
  { Boy, these headers are getting annoying. }
  Inc( bmpBuffer, SizeOf(TBitmapFileHeader) );
  PbmpInfoR := PBitmapInfoHeader(bmpBuffer);

  { Set bmpBuffer to point to the original bitmap bits. }
  Inc(bmpBuffer, SizeOf(PbmpInfoR^));
  { Set the ColumnZero pointer to point to, uh, column zero. }
  PbmpBufferColumnZero := bmpBuffer;

  with PbmpInfoR^ do
  begin
    BytesPerPixel := biBitCount shr 3;
    { ScanLines are DWORD aligned. }
    BytesPerScanLine := ((((biWidth * biBitCount) + 31) div 32) * SizeOf(DWORD));
    BytesPerScanLineR := ((((biHeight * biBitCount) + 31) div 32) * SizeOf(DWORD));

    { The TMemoryStream that will hold the rotated bits. }
    MemoryStreamR := TMemoryStream.Create;
    {
     Set size for rotated bitmap. Might be different from source size
     due to DWORD aligning.
    }
    MemoryStreamR.SetSize(BITMAP_HEADER_SIZE  + BytesPerScanLineR * biWidth);
  end;

  { Copy the headers from the source bitmap. }
  MemoryStream.Seek(0, soFromBeginning);
  MemoryStreamR.CopyFrom(MemoryStream, BITMAP_HEADER_SIZE);

  { Here's the buffer we're going to rotate. }
  bmpBufferR := MemoryStreamR.Memory;
  { Skip the headers, yadda yadda yadda... }
  Inc(bmpBufferR, BITMAP_HEADER_SIZE);

  {
   Set up PbmpBufferRFirstScanLine and advance it to end of the first scan
   line of bmpBufferR.
  }
  PbmpBufferRFirstScanLine := bmpBufferR;
  Inc(PbmpBufferRFirstScanLine, (PbmpInfoR^.biHeight - 1) * BytesPerPixel);

  { Here's the meat. Loop through the pixels and rotate appropriately. }

  { Remember that DIBs have their origins opposite from DDBs. }
  for Y := 1 to PbmpInfoR^.biHeight do
  begin
    PbmpBuffer := PbmpBufferColumnZero;
    PbmpBufferR := PbmpBufferRFirstScanLine;

    for X := 1 to PbmpInfoR^.biWidth do
    begin
      for T := 1 to BytesPerPixel do
      begin
        PbmpBufferR^ := PbmpBuffer^;
        Inc(PbmpBufferR);
        Inc(PbmpBuffer);
      end;
      Dec(PbmpBufferR, BytesPerPixel);
      Inc(PbmpBufferR, BytesPerScanLineR);
    end;

    Inc(PbmpBufferColumnZero, BytesPerScanLine);
    Dec(PbmpBufferRFirstScanLine, BytesPerPixel);
  end;

  { Done with the source bits. }
  MemoryStream.Free;

  { Now set PbmpInfoR to point to the rotated bitmap's info header. }
  PbmpBufferR := MemoryStreamR.Memory;
  Inc( PbmpBufferR, SizeOf(TBitmapFileHeader) );
  PbmpInfoR := PBitmapInfoHeader(PbmpBufferR);

  { Swap the width and height of the rotated bitmap's info header. }
  with PbmpInfoR^ do
  begin
    T := biHeight;
    biHeight := biWidth;
    biWidth := T;
  end;

  ABitmap := TBitmap.Create;

  { Spin back to the very beginning. }
  MemoryStreamR.Seek(0, soFromBeginning);
  ABitmap.LoadFromStream(MemoryStreamR);

  MemoryStreamR.Free;
end;