本文整理自网络，侵删。
验证码识别之旋转位图
1. 函数
// Bitmaps must be 24 bit pixel format.
// Angle is in degrees.
function RotateBitmap(Bitmap: TBitmap; Angle: Double; Color: TColor): TBitmap;
const
MaxPixelCount = 32768;
type
PRGBTripleArray = ^TRGBTripleArray;
TRGBTripleArray = array[0..MaxPixelCount] of TRGBTriple;
var
CosTheta: Extended;
SinTheta: Extended;
xSrc, ySrc: Integer;
xDst, yDst: Integer;
xODst, yODst: Integer;
xOSrc, yOSrc: Integer;
xPrime, yPrime: Integer;
srcRow, dstRow: PRGBTripleArray;
begin
Result := TBitmap.Create;
SinCos(Angle * Pi / 180, SinTheta, CosTheta);
if (SinTheta * CosTheta) < 0 then
begin
Result.Width := Round(Abs(Bitmap.Width * CosTheta - Bitmap.Height * SinTheta));
Result.Height := Round(Abs(Bitmap.Width * SinTheta - Bitmap.Height * CosTheta));
end
else
begin
Result.Width := Round(Abs(Bitmap.Width * CosTheta + Bitmap.Height * SinTheta));
Result.Height := Round(Abs(Bitmap.Width * SinTheta + Bitmap.Height * CosTheta));
end;
with Result.Canvas do
begin
Brush.Color := Color;
Brush.Style := bsSolid;
FillRect(ClipRect);
end;
Result.PixelFormat := pf24bit;
Bitmap.PixelFormat := pf24bit;
xODst := Result.Width div 2;
yODst := Result.Height div 2;
xOSrc := Bitmap.Width div 2;
yOSrc := Bitmap.Height div 2;
for ySrc := Max(Bitmap.Height, Result.Height)-1 downto 0 do
begin
yPrime := ySrc - yODst;
for xSrc := Max(Bitmap.Width, Result.Width)-1 downto 0 do
begin
xPrime := xSrc - xODst;
xDst := Round(xPrime * CosTheta - yPrime * SinTheta) + xOSrc;
yDst := Round(xPrime * SinTheta + yPrime * CosTheta) + yOSrc;
if (yDst >= 0) and (yDst < Bitmap.Height) and
(xDst >= 0) and (xDst < Bitmap.Width) and
(ySrc >= 0) and (ySrc < Result.Height) and
(xSrc >= 0) and (xSrc < Result.Width) then
begin
srcRow := Bitmap.ScanLine[yDst];
dstRow := Result.Scanline[ySrc];
dstRow[xSrc] := srcRow[xDst];
end;
end;
end;
end;
2. 调用例子：
Image2.Picture.Assign(RotateBitmap(Image1.Picture.Bitmap, 30, clWhite));
//将Image1的位图旋转30度后显示在Image2上
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