How to mirror and rotate bitmaps

Problem/Question/Abstract:

How to mirror and rotate bitmaps

Answer:

{Turn off Range Checking because of ARRAY[0..0] construct below}

{$R-}

unit Bitmap;

interface

uses
  Windows, Graphics;

procedure MirrorHorizontal(Bitmap: TBitmap);
procedure MirrorVertical(Bitmap: TBitmap);
procedure Rotate90Degrees(Bitmap: TBitmap);
procedure Rotate270Degrees(Bitmap: TBitmap);
procedure Rotate180Degrees(Bitmap: TBitmap);

implementation

uses
  dialogs, Classes, SysUtils;

type
  EBitmapError = class(Exception);
  TRGBArray = array[0..0] of TRGBTriple;
  pRGBArray = ^TRGBArray;

procedure MirrorHorizontal(Bitmap: TBitmap);
var
  i, j, w: Integer;
  RowIn: pRGBArray;
  RowOut: pRGBArray;
begin
  w := bitmap.width * sizeof(TRGBTriple);
  GetMem(rowin, w);
  for j := 0 to Bitmap.Height - 1 do
  begin
    move(Bitmap.Scanline[j]^, rowin^, w);
    rowout := Bitmap.Scanline[j];
    for i := 0 to Bitmap.Width - 1 do
      rowout[i] := rowin[Bitmap.Width - 1 - i];
  end;
  bitmap.Assign(bitmap);
  FreeMem(rowin);
end;

procedure MirrorVertical(Bitmap: TBitmap);
var
  j, w: Integer;
  help: TBitmap;
begin
  help := TBitmap.Create;
  help.Width := Bitmap.Width;
  help.Height := Bitmap.Height;
  help.PixelFormat := Bitmap.PixelFormat;
  w := Bitmap.Width * sizeof(TRGBTriple);
  for j := 0 to Bitmap.Height - 1 do
    move(Bitmap.Scanline[j]^, Help.Scanline[Bitmap.Height - 1 - j]^, w);
  Bitmap.Assign(help);
  help.free;
end;

type
  THelpRGB = packed record
    rgb: TRGBTriple;
    dummy: byte;
  end;

procedure Rotate270Degrees(Bitmap: TBitmap);
var
  aStream: TMemorystream;
  header: TBITMAPINFO;
  dc: hDC;
  P: ^THelpRGB;
  x, y, b, h: Integer;
  RowOut: pRGBArray;
begin
  aStream := TMemoryStream.Create;
  aStream.SetSize(Bitmap.Height * Bitmap.Width * 4);
  with header.bmiHeader do
  begin
    biSize := SizeOf(TBITMAPINFOHEADER);
    biWidth := Bitmap.Width;
    biHeight := Bitmap.Height;
    biPlanes := 1;
    biBitCount := 32;
    biCompression := 0;
    biSizeimage := aStream.Size;
    biXPelsPerMeter := 1;
    biYPelsPerMeter := 1;
    biClrUsed := 0;
    biClrImportant := 0;
  end;
  dc := GetDC(0);
  P := aStream.Memory;
  GetDIBits(dc, Bitmap.Handle, 0, Bitmap.Height, P, header, dib_RGB_Colors);
  ReleaseDC(0, dc);
  b := bitmap.Height; {rotate}
  h := bitmap.Width; {rotate}
  bitmap.Width := b;
  bitmap.height := h;
  for y := 0 to (h - 1) do
  begin
    rowOut := Bitmap.ScanLine[(h - 1) - y];
    P := aStream.Memory; {reset pointer}
    inc(p, y);
    for x := (b - 1) downto 0 do
    begin
      rowout[x] := p^.rgb;
      inc(p, h);
    end;
  end;
  aStream.Free;
end;

procedure Rotate90Degrees(Bitmap: TBitmap);
var
  aStream: TMemorystream;
  header: TBITMAPINFO;
  dc: hDC;
  P: ^THelpRGB;
  x, y, b, h: Integer;
  RowOut: pRGBArray;
begin
  aStream := TMemoryStream.Create;
  aStream.SetSize(Bitmap.Height * Bitmap.Width * 4);
  with header.bmiHeader do
  begin
    biSize := SizeOf(TBITMAPINFOHEADER);
    biWidth := Bitmap.Width;
    biHeight := Bitmap.Height;
    biPlanes := 1;
    biBitCount := 32;
    biCompression := 0;
    biSizeimage := aStream.Size;
    biXPelsPerMeter := 1;
    biYPelsPerMeter := 1;
    biClrUsed := 0;
    biClrImportant := 0;
  end;
  dc := GetDC(0);
  P := aStream.Memory;
  GetDIBits(dc, Bitmap.Handle, 0, Bitmap.Height, P, header, dib_RGB_Colors);
  ReleaseDC(0, dc);
  b := bitmap.Height; {rotate}
  h := bitmap.Width; {rotate}
  bitmap.Width := b;
  bitmap.height := h;
  for y := 0 to (h - 1) do
  begin
    rowOut := Bitmap.ScanLine[y];
    P := aStream.Memory; {reset pointer}
    inc(p, y);
    for x := 0 to (b - 1) do
    begin
      rowout[x] := p^.rgb;
      inc(p, h);
    end;
  end;
  aStream.Free;
end;

procedure Rotate180Degrees(Bitmap: TBitmap);
var
  i, j: Integer;
  rowIn: pRGBArray;
  rowOut: pRGBArray;
  help: TBitmap;
begin
  help := TBitmap.Create;
  help.Width := Bitmap.Width;
  help.Height := Bitmap.Height;
  help.PixelFormat := Bitmap.PixelFormat;
  < {only pf24bit for now}
  for j := 0 to Bitmap.Height - 1 do
  begin
    rowIn := Bitmap.ScanLine[j];
    rowOut := help.ScanLine[Bitmap.Height - j - 1];
    for i := 0 to Bitmap.Width - 1 do
      rowOut[Bitmap.Width - i - 1] := rowIn[i]
  end;
  bitmap.assign(help);
  help.free;
end;

end.