The purpose of this program, FlipReverseRotate.EXE, is to demonstrate how to

flip (top-to-bottom) and/or

reverse (left-to-right)

a bitmap in memory and display the results on the screen.

Three methods to flip/reverse are compared:

Scanline, CopyRect, StretchBlt.

In addition, a bitmap can be rotated any multiple of 90 degrees,

namely 0, 90, 180, or 270 degrees counterclockwise, but only with the Scanline method.

// The FlipReverseRotate Library provides three functions to flip and/or// reverse a bitmap.  You can choose which approach you'd like to use from the// three methods to flip or reverse a bitmap:  ScanLine, CopyRect, StretchBlt.//// A "Flip" operation takes the top of an image to the bottom and the bottom of// the image to the top.  It is a reflection along a horizontal line in the// middle of an image.//// A "Reverse" operation takes the left of an image to the right and the right// of the image to the left.  It is a reflection along a vertical line in the// middle of an image.//// Any Flip/Reverse operation is commutative, i.e., the flip and reverse can// be performed in any order to get the same result.  A flip followed by a// reverse is the same as a reverse followed by a flip.//// A "rotate" operation spins an image 0, 90, 180 or 270 degrees around an// axis in the center of the image.//// A flip/reverse operation along with a rotation is not commutative in general.// A flip followed by a rotation will not always result in the same image as a// rotation followed by a flip.  The rotation here ALWAYS follows any flip and/or// reversal.//// The examples here are intended for use with bitmaps that have 24 bits/pixel.// Palettes may be lost on 256-color bitmaps.//// Copyright (C) 1998, Earl F. Glynn.  All Rights Reserved.// May be used freely for non-comercial use.unit FlipReverseRotateLibrary;interfaceuses  Dialogs,  Windows, // TRGBTriple (put here to avoid TBitmap conflict in Implementation)  Graphics; // TBitmap// Flip/Reverse functions by Methodfunction FlipReverseScanLine( const Flip, Reverse : BOOLEAN;  const Bitmap : TBitmap ) : TBitmap;function FlipReverseCopyRect( const Flip, Reverse : BOOLEAN;  const Bitmap : TBitmap ) : TBitmap;function FlipReverseStretchBlt( const Flip, Reverse : BOOLEAN;  const Bitmap : TBitmap ) : TBitmap;// The Rotation function is only for the Scanline Method.// Note:  Windows NT supports a "plgblt" API call that can be used to rotate// images.function RotateScanline90( const angle : INTEGER; const Bitmap : TBitmap )  : TBitmap;implementationuses  Classes, // Rect  SysUtils; // Exceptionconst  MaxPixelCount = 65536; // or some other arbitrarily large valuetype  EBitmapError = class( Exception );  TRGBArray = array [ 0 .. MaxPixelCount - 1 ] of TRGBTriple;  pRGBArray = ^TRGBArray;  /// ///function FlipReverseScanLine( const Flip, Reverse : BOOLEAN;  const Bitmap : TBitmap ) : TBitmap;var  i : INTEGER;  j : INTEGER;  RowIn : pRGBArray;  RowOut : pRGBArray;begin  if Bitmap.PixelFormat <> pf24bit then    raise EBitmapError.Create( 'Can Flip/Reverse only 24-bit bitmap' );  RESULT := TBitmap.Create;  RESULT.Width := Bitmap.Width;  RESULT.Height := Bitmap.Height;  RESULT.PixelFormat := Bitmap.PixelFormat;  for j := 0 to Bitmap.Height - 1 do  begin    RowIn := Bitmap.Scanline[ j ];    if Flip then      RowOut := RESULT.Scanline[ Bitmap.Height - 1 - j ]    else      RowOut := RESULT.Scanline[ j ];    // Optimization technique:  Use two FOR loops so IF is outside of inner loop    if Reverse then    begin      for i := 0 to Bitmap.Width - 1 do        RowOut[ i ] := RowIn[ Bitmap.Width - 1 - i ]    end    else    begin      for i := 0 to Bitmap.Width - 1 do        RowOut[ i ] := RowIn[ i ]    end  endend {
      FlipReverseScanLine };/// ///// This function implements a suggestion by David Ullrich in a July 25, 1997// post to comp.lang.pascal.delphi.misc.//// The Graphics.PAS unit shows that CopyRect calls the Windows StretchBlt API// function.function FlipReverseCopyRect( const Flip, Reverse : BOOLEAN;  const Bitmap : TBitmap ) : TBitmap;var  Bottom : INTEGER;  Left : INTEGER;  Right : INTEGER;  Top : INTEGER;begin  RESULT := TBitmap.Create;  RESULT.Width := Bitmap.Width;  RESULT.Height := Bitmap.Height;  RESULT.PixelFormat := Bitmap.PixelFormat;  // Flip Top to Bottom  if Flip then  begin    // Unclear why extra "-1" is needed here.    Top := Bitmap.Height - 1;    Bottom := -1  end  else  begin    Top := 0;    Bottom := Bitmap.Height  end;  // Reverse Left to Right  if Reverse then  begin    // Unclear why extra "-1" is needed here.    Left := Bitmap.Width - 1;    Right := -1;  end  else  begin    Left := 0;    Right := Bitmap.Width;  end;  RESULT.Canvas.CopyRect( Rect( Left, Top, Right, Bottom ), Bitmap.Canvas,    Rect( 0, 0, Bitmap.Width, Bitmap.Height ) );end {
      FlipReverseCopyRect };/// ///function FlipReverseStretchBlt( const Flip, Reverse : BOOLEAN;  const Bitmap : TBitmap ) : TBitmap;var  Bottom : INTEGER;  Left : INTEGER;  Right : INTEGER;  Top : INTEGER;begin  RESULT := TBitmap.Create;  RESULT.Width := Bitmap.Width;  RESULT.Height := Bitmap.Height;  RESULT.PixelFormat := Bitmap.PixelFormat;  // Flip Top to Bottom  if Flip then  begin    // Unclear why extra "-1" is needed here.    Top := Bitmap.Height - 1;    Bottom := -1  end  else  begin    Top := 0;    Bottom := Bitmap.Height  end;  // Reverse Left to Right  if Reverse then  begin    // Unclear why extra "-1" is needed here.    Left := Bitmap.Width - 1;    Right := -1;  end  else  begin    Left := 0;    Right := Bitmap.Width;  end;  StretchBlt( RESULT.Canvas.Handle, Left, Top, Right - Left, Bottom - Top,    Bitmap.Canvas.Handle, 0, 0, Bitmap.Width, Bitmap.Height, cmSrcCopy );end {
      FlipReverseStretchBlt };/// ///// Rotate 24-bits/pixel Bitmap any multiple of 90 degrees.function RotateScanline90( const angle : INTEGER; const Bitmap : TBitmap )  : TBitmap;// These four internal functions parallel the four cases in rotating a// bitmap using the Pixels property.  See the RotatePixels example on// the Image Processing page of efg's Computer Lab for an example of the// use of the Pixels property (which is very slow).// A Bitmap.Assign could be used for a simple copy.  A complete example// using ScanLine is included here to help explain the other three cases.  function SimpleCopy : TBitmap;  var    i : INTEGER;    j : INTEGER;    RowIn : pRGBArray;    RowOut : pRGBArray;  begin    RESULT := TBitmap.Create;    RESULT.Width := Bitmap.Width;    RESULT.Height := Bitmap.Height;    RESULT.PixelFormat := Bitmap.PixelFormat; // only pf24bit for now    // Out[i, j] = In[i, j]    for j := 0 to Bitmap.Height - 1 do    begin      RowIn := Bitmap.Scanline[ j ];      RowOut := RESULT.Scanline[ j ];      // Could optimize the following by using a function like CopyMemory      // from the Windows unit.      for i := 0 to Bitmap.Width - 1 do      begin        // Why does this crash with RowOut[i] := RowIn[i]?  Alignment?        // Use this longer form as workaround.        with RowOut[ i ] do        begin          rgbtRed := RowIn[ i ].rgbtRed;          rgbtGreen := RowIn[ i ].rgbtGreen;          rgbtBlue := RowIn[ i ].rgbtBlue;        end      end    end  end {
      SimpleCopy };  function Rotate90DegreesCounterClockwise : TBitmap;  var    i : INTEGER;    j : INTEGER;    RowIn : pRGBArray;  begin    RESULT := TBitmap.Create;    RESULT.Width := Bitmap.Height;    RESULT.Height := Bitmap.Width;    RESULT.PixelFormat := Bitmap.PixelFormat; // only pf24bit for now    // Out[j, Right - i - 1] = In[i, j]    for j := 0 to Bitmap.Height - 1 do    begin      RowIn := Bitmap.Scanline[ j ];      for i := 0 to Bitmap.Width - 1 do        pRGBArray( RESULT.Scanline[ Bitmap.Width - i - 1 ] )[ j ] := RowIn[ i ]    end  end {
      Rotate90DegreesCounterClockwise };// Could use Rotate90DegreesCounterClockwise twice to get a// Rotate180DegreesCounterClockwise.  Rotating 180 degrees is the same// as a Flip and Reverse  function Rotate180DegreesCounterClockwise : TBitmap;  var    i : INTEGER;    j : INTEGER;    RowIn : pRGBArray;    RowOut : pRGBArray;  begin    RESULT := TBitmap.Create;    RESULT.Width := Bitmap.Width;    RESULT.Height := Bitmap.Height;    RESULT.PixelFormat := Bitmap.PixelFormat; // only pf24bit for now    // Out[Right - i - 1, Bottom - j - 1] = In[i, j]    for j := 0 to Bitmap.Height - 1 do    begin      RowIn := Bitmap.Scanline[ j ];      RowOut := RESULT.Scanline[ Bitmap.Height - j - 1 ];      for i := 0 to Bitmap.Width - 1 do        RowOut[ Bitmap.Width - i - 1 ] := RowIn[ i ]    end  end {
      Rotate180DegreesCounterClockwise };// Could use Rotate90DegreesCounterClockwise three times to get a// Rotate270DegreesCounterClockwise  function Rotate270DegreesCounterClockwise : TBitmap;  var    i : INTEGER;    j : INTEGER;    RowIn : pRGBArray;  begin    RESULT := TBitmap.Create;    RESULT.Width := Bitmap.Height;    RESULT.Height := Bitmap.Width;    RESULT.PixelFormat := Bitmap.PixelFormat; // only pf24bit for now    // Out[Bottom - j - 1, i] = In[i, j]    for j := 0 to Bitmap.Height - 1 do    begin      RowIn := Bitmap.Scanline[ j ];      for i := 0 to Bitmap.Width - 1 do        pRGBArray( RESULT.Scanline[ i ] )[ Bitmap.Height - j - 1 ] := RowIn[ i ]    end  end {
      Rotate270DegreesCounterClockwise };begin  if Bitmap.PixelFormat <> pf24bit then    raise EBitmapError.Create( 'Can Rotate90 only 24-bit bitmap' );  if ( angle >= 0 ) and ( angle mod 90 <> 0 ) then    raise EBitmapError.Create      ( 'Rotate90:  Angle not positive multiple of 90 degrees' );  case ( angle div 90 ) mod 4 of    0 :      RESULT := SimpleCopy;    1 :      RESULT := Rotate90DegreesCounterClockwise;    // Anticlockwise for the Brits    2 :      RESULT := Rotate180DegreesCounterClockwise;    3 :      RESULT := Rotate270DegreesCounterClockwise  else    RESULT := nil // avoid compiler warning  end;end {
      RotateScanline90 };end.