小雪推荐的网站的上的：
CONST
MaxPixelCount = 32768;
TYPE
TRGBTripleArray = ARRAY[0..MaxPixelCount-1] OF TRGBTriple;
pRGBTripleArray = ^TRGBTripleArray;
...
// "Simple" approach. For pixel (i,j), use "reverse" rotation to find
// where the rotated pixel must have been before the rotation.
// Don't bother with center of pixel adjustment.
// Assumes input BitmapOriginal has PixelFormat = pf24bit.
FUNCTION RotateBitmapMethod1 (CONST BitmapOriginal: TBitmap;
CONST iRotationAxis, jRotationAxis: INTEGER;
CONST AngleOfRotation: DOUBLE {radians} ): TBitmap;
VAR
cosTheta : EXTENDED;
i : INTEGER;
iOriginal : INTEGER;
iPrime : INTEGER;
j : INTEGER;
jOriginal : INTEGER;
jPrime : INTEGER;
RowOriginal: pRGBTripleArray;
RowRotated : pRGBTRipleArray;
sinTheta : EXTENDED;
BEGIN
// The size of BitmapRotated is the same as BitmapOriginal. PixelFormat
// must also match since 24-bit GBR triplets are assumed in ScanLine.
RESULT := TBitmap.Create;
RESULT.Width := BitmapOriginal.Width;
RESULT.Height := BitmapOriginal.Height;
RESULT.PixelFormat := pf24bit; // Force this
// Get SIN and COS in single call from math library
sincos(AngleOfRotation, sinTheta, cosTheta);
// If no math library, then use this:
// sinTheta := SIN(AngleOfRotation);
// cosTheta := COS(AngleOfRotation);
// Step through each row of rotated image.
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);
// Make sure (iOriginal, jOriginal) is in BitmapOriginal. If not,
// assign blue color to corner points.
IF (iOriginal >= 0) AND (iOriginal <= BitmapOriginal.Width-1) AND
(jOriginal >= 0) AND (jOriginal <= BitmapOriginal.Height-1)
THEN BEGIN
// Assign pixel from rotated space to current pixel in BitmapRotated
RowOriginal := BitmapOriginal.Scanline[jOriginal];
RowRotated := RowOriginal[iOriginal]
END
ELSE BEGIN
RowRotated.rgbtBlue := 255; // assign "corner" color
RowRotated.rgbtGreen := 0;
RowRotated.rgbtRed := 0
END
END
END
END {RotateBitmapMethod1};
