Girar em tantos graus?

FUNCTION RotateBitmapMethod1(CONST BitmapOriginal: TBitmap;
                             CONST iRotationAxis, jRotationAxis: INTEGER;
                             CONST AngleOfRotation: DOUBLE; // em radianos
                             VAR RotateMilliseconds:  DWORD): TBitmap;
  VAR
    cosTheta       :  EXTENDED;
    i              :  INTEGER;
    iOriginal      :  INTEGER;
    iPrime         :  INTEGER;
    j              :  INTEGER;
    jOriginal      :  INTEGER;
    jPrime         :  INTEGER;
    RowOriginal    :  pRGBTripleArray;
    RowRotated     :  pRGBTRipleArray;
    sinTheta       :  EXTENDED;
    StartTime      :  DWORD;
begin
  RESULT := TBitmap.Create;
  RESULT.Width  := BitmapOriginal.Width;
  RESULT.Height := BitmapOriginal.Height;
  RESULT.PixelFormat := pf24bit;

  StartTime := GetTickCount;

  sincos(AngleOfRotation, sinTheta, cosTheta);

  FOR j := RESULT.Height-1 DOWNTO 0 DO
  BEGIN
    RowRotated  := RESULT.Scanline[j];
    jPrime := j - jRotationAxis;

    FOR i := RESULT.Width-1 DOWNTO 0 DO
    BEGIN
      iPrime := i - iRotationAxis;
      iOriginal := iRotationAxis + ROUND(iPrime * CosTheta - jPrime * sinTheta);
      jOriginal := jRotationAxis + ROUND(iPrime * sinTheta + jPrime * cosTheta);

      IF   (iOriginal >= 0) AND (iOriginal <= BitmapOriginal.Width-1) AND
           (jOriginal >= 0) AND (jOriginal <= BitmapOriginal.Height-1)
      THEN BEGIN
        RowOriginal   := BitmapOriginal.Scanline[jOriginal];
        RowRotated[i] := RowOriginal[iOriginal]
      END
      ELSE BEGIN
        RowRotated[i].rgbtBlue  := 255;  // Nessas três linhas
        RowRotated[i].rgbtGreen := 0;    // de código você altera
        RowRotated[i].rgbtRed   := 0;    // a cor de fundo da figura final
      END

    END
  END;
  RotateMilliseconds := GetTickCount - StartTime;
END;

  const
    MaxPixelCount   =  32768;

  type
    TRGBTripleArray  =  ARRAY[0..MaxPixelCount-1] OF TRGBTriple;
    pRGBTripleArray  =  ^TRGBTripleArray;