Here's code to rotate a bitmap 90 degrees

The new unit has three routines: RotateBitmap90DegreesClockwise, RotateBitmap90DegreesCounterClockwise, and RotateBitmap180Degrees. All three take a TBitmap as a var and rotate it the appropriate way.

Two caveats: This still doesn't quite work for Delphi3. Somehow some noise gets introduced into the edges. I think it might be a bug in TBitmap's LoadFromStream method, but it's probably my fault. However, there are other solutions using the ScanLine property, so that isn't much of a problem. Second, this doesn't work if the bitmap is RLE compressed. 4- and 8-byte bitmaps can be run-length encoded, and they will be stored that way in memory until a handle is needed. If the bitmap is compressed, just grab the canvas's handle

ABitmap.Canvas.Handle;

This also assigns it to a device context (i.e. the screen), and will probably blow it up to 24-bit format. Kind of a compromise.

Anyway, the unit I'm attaching works in Delphi 1 and 2 for monochrome, 4-, 8-, 16-, 24-, and 32-bit bitmaps (but not for 4- and 8-bit RLE compressed guys, as I mentioned above).

unit bmpRot;

interface

uses

(*$IFDEF Win32*) Windows, (*$ELSE*) WinTypes, WinProcs, (*$ENDIF*)

Classes, Graphics;

procedure RotateBitmap90DegreesCounterClockwise(var ABitmap: TBitmap);

procedure RotateBitmap90DegreesClockwise(var ABitmap: TBitmap);

procedure RotateBitmap180Degrees(var ABitmap: TBitmap);

implementation

uses

Dialogs;

(*$IFNDEF Win32*)

type

DWORD = LongInt;

TSelOfs = record

L, H: Word;

end;

procedure Win16Dec(var P: Pointer; const N: LongInt); forward;

procedure Win16Inc(var P: Pointer; const N: LongInt);

begin

if N < 0 then

Win16Dec(P, -N)

else if N > 0 then begin

Inc( TSelOfs(P).H, TSelOfs(N).H * SelectorInc );

Inc( TSelOfs(P).L, TSelOfs(N).L );

if TSelOfs(P).L < TSelOfs(N).L then Inc( TSelOfs(P).H, SelectorInc );

end;

procedure Win16Dec(var P: Pointer; const N: LongInt);

begin

if N < 0 then

Win16Inc(P, -N)

else if N > 0 then begin

if TSelOfs(N).L > TSelOfs(P).L then Dec( TSelOfs(P).H, SelectorInc );

Dec( TSelOfs(P).L, TSelOfs(N).L );

Dec( TSelOfs(P).H, TSelOfs(N).H * SelectorInc );

end;

procedure HugeShift; far; external 'KERNEL' index 113;

procedure Win16Dec(var P: Pointer; const N: LongInt); forward;

procedure Win16Inc(var HugePtr: Pointer; Amount: LongInt);

procedure HugeInc; assembler;

asm

mov ax, Amount.Word[0] { Store Amount in DX:AX. }

mov dx, Amount.Word[2]

les bx, HugePtr { Get the reference to HugePtr. }

add ax, es:[bx] { Add the offset parts. }

adc dx, 0 { Propagate carry to the high word of Amount. }

mov cx, Offset HugeShift

shl dx, cl { Shift high word of Amount for segment. }

add es:[bx+2], dx { Increment the segment of HugePtr. }

mov es:[bx], ax

end;

begin

if Amount > 0 then HugeInc else if Amount < 0 then Win16Dec(HugePtr, -Amount);

end;

procedure Win16Dec(var P: Pointer; const N: LongInt);

begin

if N < 0 then

Win16Inc(P, -N)

else if N > 0 then begin

if TSelOfs(N).L > TSelOfs(P).L then Dec( TSelOfs(P).H, SelectorInc );

Dec( TSelOfs(P).L, TSelOfs(N).L );

Dec( TSelOfs(P).H, TSelOfs(N).H * SelectorInc );

end;

(*$ENDIF*)

procedure RotateBitmap90DegreesCounterClockwise(var ABitmap: TBitmap);

const

BitsPerByte = 8;

var

{

A whole pile of variables. Some deal with one- and four-bit bitmaps only,

some deal with eight- and 24-bit bitmaps only, and some deal with both.

Any variable that ends in 'R' refers to the rotated bitmap, e.g. MemoryStream

holds the original bitmap, and MemoryStreamR holds the rotated one.

}

PbmpInfoR: PBitmapInfoHeader;

bmpBuffer, bmpBufferR: PByte;

MemoryStream, MemoryStreamR: TMemoryStream;

PbmpBuffer, PbmpBufferR: PByte;

BytesPerPixel, PixelsPerByte: LongInt;

BytesPerScanLine, BytesPerScanLineR: LongInt;

PaddingBytes: LongInt;

BitmapOffset: LongInt;

BitCount: LongInt;

WholeBytes, ExtraPixels: LongInt;

SignificantBytes, SignificantBytesR: LongInt;

ColumnBytes: LongInt;

AtLeastEightBitColor: Boolean;

T: LongInt;

procedure NonIntegralByteRotate; (* nested *)

{

This routine rotates bitmaps with fewer than 8 bits of information per pixel,

namely monochrome (1-bit) and 16-color (4-bit) bitmaps. Note that there are

no such things as 2-bit bitmaps, though you might argue that Microsoft's bitmap

format is worth about 2 bits.

}

var

X, Y: LongInt;

I: LongInt;

MaskBits, CurrentBits: Byte;

FirstMask, LastMask: Byte;

PFirstScanLine: PByte;

FirstIndex, CurrentBitIndex: LongInt;

ShiftRightAmount, ShiftRightStart: LongInt;

begin

(*$IFDEF Win32*)

Inc(PbmpBuffer, BytesPerScanLine * (PbmpInfoR^.biHeight - 1) );

(*$ELSE*)

Win16Inc( Pointer(PbmpBuffer), BytesPerScanLine * (PbmpInfoR^.biHeight - 1) );

(*$ENDIF*)

{ PFirstScanLine advances along the first scan line of bmpBufferR. }

PFirstScanLine := bmpBufferR;

{ Set up the indexing. }

FirstIndex := BitsPerByte - BitCount;

{

Set up the bit masks:

For a monochrome bitmap,

LastMask := 00000001 and

FirstMask := 10000000

For a 4-bit bitmap,

LastMask := 00001111 and

FirstMask := 11110000

We'll shift through these such that the CurrentBits and the MaskBits will go

For a monochrome bitmap:

10000000, 01000000, 00100000, 00010000, 00001000, 00000100, 00000010, 00000001

For a 4-bit bitmap:

11110000, 00001111

The CurrentBitIndex denotes how far over the right-most bit would need to

shift to get to the position of CurrentBits. For example, if we're on the

eleventh column of a monochrome bitmap, then CurrentBits will equal

11 mod 8 := 3, or the 3rd-to-the-leftmost bit. Thus, the right-most bit

would need to shift four places over to get anded correctly with

CurrentBits. CurrentBitIndex will store this value.

}

LastMask := 1 shl BitCount - 1;

FirstMask := LastMask shl FirstIndex;

CurrentBits := FirstMask;

CurrentBitIndex := FirstIndex;

ShiftRightStart := BitCount * (PixelsPerByte - 1);

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

{ Remember that DIBs have their origins opposite from DDBs. }

{ The Y counter holds the current row of the source bitmap. }

for Y := 1 to PbmpInfoR^.biHeight do begin

PbmpBufferR := PFirstScanLine;

{

The X counter holds the current column of the source bitmap. We only

deal with completely filled bytes here. Should there be an extra 'partial'

byte, we'll deal with that below.

}

for X := 1 to WholeBytes do begin

{

Pick out the bits, starting with 10000000 for monochromes and

11110000 for 4-bit guys.

}

MaskBits := FirstMask;

{

ShiftRightAmount is the amount we need to shift the current bit all

the way to the right.

}

ShiftRightAmount := ShiftRightStart;

for I := 1 to PixelsPerByte do begin

{

Here's the doozy. Take the rotated bitmap's current byte and mask it

with not CurrentBits. This zeros out the CurrentBits only, and leaves

everything else unchanged. Example: For a monochrome bitmap, if we

were on the 11th column as above, we would need to zero out the

3rd-to-left bit, so we would take PbmpBufferR^ and 11011111.

Now consider our current source byte. For monochrome bitmaps, we're

going to loop through each bit, for a total of eight pixels. For

4-bit bitmaps, we're going to loop through the bits four at a time,

for a total of two pixels. Either way, we do this by masking it with

MaskBits ('PbmpBuffer^ and MaskBits'). Now we need to get the bit(s)

into the same column(s) that CurrentBits reflects. We do this by

shifting them to the right-most part of the byte ('shr

ShiftRightAmount'), and then shifting left by our aforementioned

CurrentBitIndex ('shl CurrentBitIndex'). This is because, although a

right-shift of -n should just be a left-shift of +n, it doesn't work

that way, at least in Delphi. So we just start from scratch by putting

everything as far right as we can.

Finally, we have our source bit(s) shifted to the appropriate place,

with nothing but zeros around. Simply or it with PbmpBufferR^ (which

had its CurrentBits zeroed out, remember?) and we're done.

Yeah, sure. "Simply". Duh.

}

PbmpBufferR^ := ( PbmpBufferR^ and not CurrentBits ) or

( (PbmpBuffer^ and MaskBits) shr ShiftRightAmount shl CurrentBitIndex );

{ Move the MaskBits over for the next iteration. }

MaskBits := MaskBits shr BitCount;

(*$IFDEF Win32*)

{ Move our pointer to the rotated-bitmap buffer up one scan line. }

Inc(PbmpBufferR, BytesPerScanLineR);

{ We don't need to shift as far to the right the next time around. }

Dec(ShiftRightAmount, BitCount);

(*$ELSE*)

Win16Inc( Pointer(PbmpBufferR), BytesPerScanLineR );

Win16Dec( Pointer(ShiftRightAmount), BitCount );

(*$ENDIF*)

end;

(*$IFDEF Win32*)

Inc(PbmpBuffer);

(*$ELSE*)

Win16Inc( Pointer(PbmpBuffer), 1 );

(*$ENDIF*)

end;

{ If there's a partial byte, take care of it now. }

if ExtraPixels <> 0 then begin

{ Do exactly the same crap as in the loop above. }

MaskBits := FirstMask;

ShiftRightAmount := ShiftRightStart;

for I := 1 to ExtraPixels do begin

PbmpBufferR^ := ( PbmpBufferR^ and not CurrentBits ) or

( (PbmpBuffer^ and MaskBits) shr ShiftRightAmount shl CurrentBitIndex );

MaskBits := MaskBits shr BitCount;

(*$IFDEF Win32*)

Inc(PbmpBufferR, BytesPerScanLineR);

(*$ELSE*)

Win16Inc( Pointer(PbmpBufferR), BytesPerScanLineR );

(*$ENDIF*)

Dec(ShiftRightAmount, BitCount);

end;

(*$IFDEF Win32*)

Inc(PbmpBuffer);

(*$ELSE*)

Win16Inc( Pointer(PbmpBuffer), 1 );

(*$ENDIF*)

end;

(*$IFDEF Win32*)

{ Skip the padding. }

Inc(PbmpBuffer, PaddingBytes);

{

Back up the scan line you just traversed, and go one more to get set for

the next row.

}

Dec(PbmpBuffer, BytesPerScanLine shl 1);

(*$ELSE*)

Win16Inc( Pointer(PbmpBuffer), PaddingBytes );

Win16Dec( Pointer(PbmpBuffer), BytesPerScanLine shl 1 );

(*$ENDIF*)

if CurrentBits = LastMask then begin

{ We're at the end of this byte. Start over on another column. }

CurrentBits := FirstMask;

CurrentBitIndex := FirstIndex;

{ Go to the bottom of the rotated bitmap's column, but one column over. }

(*$IFDEF Win32*)

Inc(PFirstScanLine);

(*$ELSE*)

Win16Inc( Pointer(PFirstScanLine), 1 );

(*$ENDIF*)

end

else begin

{ Continue filling this byte. }

CurrentBits := CurrentBits shr BitCount;

Dec(CurrentBitIndex, BitCount);

end;

end; { procedure NonIntegralByteRotate (* nested *) }

procedure IntegralByteRotate; (* nested *)

var

X, Y: LongInt;

(*$IFNDEF Win32*)

I: Integer;

(*$ENDIF*)

begin

{ Advance PbmpBufferR to the last column of the first scan line of bmpBufferR. }

(*$IFDEF Win32*)

Inc(PbmpBufferR, SignificantBytesR - BytesPerPixel);

(*$ELSE*)

Win16Inc( Pointer(PbmpBufferR), SignificantBytesR - BytesPerPixel );

(*$ENDIF*)

{ 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

for X := 1 to PbmpInfoR^.biWidth do begin

{ Copy the pixels. }

(*$IFDEF Win32*)

Move(PbmpBuffer^, PbmpBufferR^, BytesPerPixel);

Inc(PbmpBuffer, BytesPerPixel);

Inc(PbmpBufferR, BytesPerScanLineR);

(*$ELSE*)

for I := 1 to BytesPerPixel do begin

PbmpBufferR^ := PbmpBuffer^;

Win16Inc( Pointer(PbmpBuffer), 1 );

Win16Inc( Pointer(PbmpBufferR), 1 );

end;

Win16Inc( Pointer(PbmpBufferR), BytesPerScanLineR - BytesPerPixel);

(*$ENDIF*)

end;

(*$IFDEF Win32*)

{ Skip the padding. }

Inc(PbmpBuffer, PaddingBytes);

{ Go to the top of the rotated bitmap's column, but one column over. }

Dec(PbmpBufferR, ColumnBytes + BytesPerPixel);

(*$ELSE*)

Win16Inc( Pointer(PbmpBuffer), PaddingBytes);

Win16Dec( Pointer(PbmpBufferR), ColumnBytes + BytesPerPixel);

(*$ENDIF*)

end;

{ This is the body of procedure RotateBitmap90DegreesCounterClockwise. }

begin

{ Don't *ever* call GetDIBSizes! It screws up your bitmap. }

MemoryStream := TMemoryStream.Create;

{

To do: Set the size before-hand. This will eliminate ReAlloc overhead

for the MemoryStream. Calling GetDIBSizes would be nice, but, as mentioned

above, it corrupts the Bitmap in some cases. Some API calls will probably

take care of things, but I'm not going to mess with it right now.

}

{ An undocumented method. Nice to have around, though. }

ABitmap.SaveToStream(MemoryStream);

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

ABitmap.Free;

bmpBuffer := MemoryStream.Memory;

{ Get the offset bits. This may or may not include palette information. }

BitmapOffset := PBitmapFileHeader(bmpBuffer)^.bfOffBits;

{ Set PbmpInfoR to point to the source bitmap's info header. }

{ Boy, these headers are getting annoying. }

(*$IFDEF Win32*)

Inc( bmpBuffer, SizeOf(TBitmapFileHeader) );

(*$ELSE*)

Win16Inc( Pointer(bmpBuffer), SizeOf(TBitmapFileHeader) );

(*$ENDIF*)

PbmpInfoR := PBitmapInfoHeader(bmpBuffer);

{ Set bmpBuffer and PbmpBuffer to point to the original bitmap bits. }

bmpBuffer := MemoryStream.Memory;

(*$IFDEF Win32*)

Inc(bmpBuffer, BitmapOffset);

(*$ELSE*)

Win16Inc( Pointer(bmpBuffer), BitmapOffset );

(*$ENDIF*)

PbmpBuffer := bmpBuffer;

{

Note that we don't need to worry about version 4 vs. version 3 bitmaps,

because the fields we use -- namely biWidth, biHeight, and biBitCount --

occur in exactly the same place in both structs. So we're a bit lucky. OS/2

bitmaps, by the way, cause this to crash heinously. Sorry.

}

with PbmpInfoR^ do begin

{ ShowMessage('Compression := ' + IntToStr(biCompression)); }

BitCount := biBitCount;

{ ShowMessage('BitCount := ' + IntToStr(BitCount)); }

{ ScanLines are DWORD aligned. }

BytesPerScanLine := ((((biWidth * BitCount) + 31) div 32) * SizeOf(DWORD));

BytesPerScanLineR := ((((biHeight * BitCount) + 31) div 32) * SizeOf(DWORD));

AtLeastEightBitColor := BitCount >= BitsPerByte;

if AtLeastEightBitColor then begin

{ Don't have to worry about bit-twiddling. Cool. }

BytesPerPixel := biBitCount shr 3;

SignificantBytes := biWidth * BitCount shr 3;

SignificantBytesR := biHeight * BitCount shr 3;

{ Extra bytes required for DWORD aligning. }

PaddingBytes := BytesPerScanLine - SignificantBytes;

ColumnBytes := BytesPerScanLineR * biWidth;

end

else begin

{ One- or four-bit bitmap. Ugh. }

PixelsPerByte := SizeOf(Byte) * BitsPerByte div BitCount;

{ The number of bytes entirely filled with pixel information. }

WholeBytes := biWidth div PixelsPerByte;

{

Any extra bits that might partially fill a byte. For instance, a

monochrome bitmap that is 14 pixels wide has one whole byte and a

partial byte which has six bits actually used (the rest are garbage).

}

ExtraPixels := biWidth mod PixelsPerByte;

{

The number of extra bytes -- if any -- required to DWORD-align a

scanline.

}

PaddingBytes := BytesPerScanLine - WholeBytes;

{

If there are extra bits (i.e., they run over into a 'partial byte'),

then one of the padding bytes has already been accounted for.

}

if ExtraPixels <> 0 then Dec(PaddingBytes);

end; { if AtLeastEightBitColor then }

{ 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(BitmapOffset + BytesPerScanLineR * biWidth);

end; { with PbmpInfoR^ do }

{ Copy the headers from the source bitmap. }

MemoryStream.Seek(0, soFromBeginning);

MemoryStreamR.CopyFrom(MemoryStream, BitmapOffset);

{ Here's the buffer we're going to rotate. }

bmpBufferR := MemoryStreamR.Memory;

{ Skip the headers, yadda yadda yadda... }

(*$IFDEF Win32*)

Inc(bmpBufferR, BitmapOffset);

(*$ELSE*)

Win16Inc( Pointer(bmpBufferR), BitmapOffset );

(*$ENDIF*)

PbmpBufferR := bmpBufferR;

{ Do it. }

if AtLeastEightBitColor then

IntegralByteRotate

else

NonIntegralByteRotate;

{ Done with the source bits. }

MemoryStream.Free;

{ Now set PbmpInfoR to point to the rotated bitmap's info header. }

PbmpBufferR := MemoryStreamR.Memory;

(*$IFDEF Win32*)

Inc( PbmpBufferR, SizeOf(TBitmapFileHeader) );

(*$ELSE*)

Win16Inc( Pointer(PbmpBufferR), SizeOf(TBitmapFileHeader) );

(*$ENDIF*)

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;

biSizeImage := 0;

end;

ABitmap := TBitmap.Create;

{ Spin back to the very beginning. }

MemoryStreamR.Seek(0, soFromBeginning);

{ Load it back into ABitmap. }

ABitmap.LoadFromStream(MemoryStreamR);

MemoryStreamR.Free;

end;

procedure RotateBitmap90DegreesClockwise(var ABitmap: TBitmap);

const

BitsPerByte = 8;

var

{

A whole pile of variables. Some deal with one- and four-bit bitmaps only,

some deal with eight- and 24-bit bitmaps only, and some deal with both.

Any variable that ends in 'R' refers to the rotated bitmap, e.g. MemoryStream

holds the original bitmap, and MemoryStreamR holds the rotated one.

}

PbmpInfoR: PBitmapInfoHeader;

bmpBuffer, bmpBufferR: PByte;

MemoryStream, MemoryStreamR: TMemoryStream;

PbmpBuffer, PbmpBufferR: PByte;

BytesPerPixel, PixelsPerByte: LongInt;

BytesPerScanLine, BytesPerScanLineR: LongInt;

PaddingBytes: LongInt;

BitmapOffset: LongInt;

BitCount: LongInt;

WholeBytes, ExtraPixels: LongInt;

SignificantBytes: LongInt;

ColumnBytes: LongInt;

AtLeastEightBitColor: Boolean;

T: LongInt;

procedure NonIntegralByteRotate; (* nested *)

{

This routine rotates bitmaps with fewer than 8 bits of information per pixel,

namely monochrome (1-bit) and 16-color (4-bit) bitmaps. Note that there are

no such things as 2-bit bitmaps, though you might argue that Microsoft's bitmap

format is worth about 2 bits.

}

var

X, Y: LongInt;

I: LongInt;

MaskBits, CurrentBits: Byte;

FirstMask, LastMask: Byte;

PLastScanLine: PByte;

FirstIndex, CurrentBitIndex: LongInt;

ShiftRightAmount, ShiftRightStart: LongInt;

begin

{ Advance PLastScanLine to the first column of the last scan line of bmpBufferR. }

PLastScanLine := bmpBufferR; (*$IFDEF Win32*) Inc(PLastScanLine, BytesPerScanLineR *

(PbmpInfoR^.biWidth - 1) ); (*$ELSE*) Win16Inc( Pointer(PLastScanLine),

BytesPerScanLineR * (PbmpInfoR^.biWidth - 1) ); (*$ENDIF*)

{ Set up the indexing. }

FirstIndex := BitsPerByte - BitCount;

{

Set up the bit masks:

For a monochrome bitmap,

LastMask := 00000001 and

FirstMask := 10000000

For a 4-bit bitmap,

LastMask := 00001111 and

FirstMask := 11110000

We'll shift through these such that the CurrentBits and the MaskBits will go

For a monochrome bitmap:

10000000, 01000000, 00100000, 00010000, 00001000, 00000100, 00000010, 00000001

For a 4-bit bitmap:

11110000, 00001111

The CurrentBitIndex denotes how far over the right-most bit would need to

shift to get to the position of CurrentBits. For example, if we're on the

eleventh column of a monochrome bitmap, then CurrentBits will equal

11 mod 8 := 3, or the 3rd-to-the-leftmost bit. Thus, the right-most bit

would need to shift four places over to get anded correctly with

CurrentBits. CurrentBitIndex will store this value.

}

LastMask := 1 shl BitCount - 1;

FirstMask := LastMask shl FirstIndex;

CurrentBits := FirstMask;

CurrentBitIndex := FirstIndex;

ShiftRightStart := BitCount * (PixelsPerByte - 1);

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

{ Remember that DIBs have their origins opposite from DDBs. }

{ The Y counter holds the current row of the source bitmap. }

for Y := 1 to PbmpInfoR^.biHeight do begin

PbmpBufferR := PLastScanLine;