XFORM图像旋转有关问题

Graphics::TBitmap *bitmap1 = new Graphics::TBitmap();
Graphics::TBitmap *bitmap2 = new Graphics::TBitmap();
bitmap1 -> Assign(Image1 -> Picture -> Bitmap);
float angle = -(TrackBar2 -> Position);      //TrackBar2当前位置表示选择角度
Label3 -> Caption = IntToStr(TrackBar2 -> Position) + "°";
float RADIAN = (PI * angle) / 180 ; //均转为弧度
float cosone = (float)cos(RADIAN);
float sinone = (float)sin(RADIAN);
float point1x = (-bitmap1 -> Height * sinone); //计算旋转后的点
float point1y = (bitmap1 -> Height * cosone);
float point2x = (bitmap1 -> Width * cosone - bitmap1 -> Height * sinone);
float point2y = (bitmap1 -> Height * cosone + bitmap1 -> Width * sinone);
float point3x = (bitmap1 -> Width * cosone);
float point3y = (bitmap1 -> Width * sinone);
float minx = min((float)0, min(point1x, min(point2x, point3x)));
float miny = min((float)0, min(point1y, min(point2y, point3y)));
float maxx = max((float)0, max(point1x, max(point2x, point3x)));
float maxy = max((float)0, max(point1y, max(point2y, point3y)));
int pstW = (int)ceil(maxx - minx); //计算bitmap2的长和宽
int pstH = (int)ceil(maxy - miny);
bitmap2 -> Height = pstH;
bitmap2 -> Width = pstW;
SetGraphicsMode(bitmap2 -> Canvas -> Handle, GM_ADVANCED); //改变模式
XFORM xform;
float cenx = (bitmap1 -> Width) / 2; //原图中心
float ceny = (bitmap1 -> Height) / 2;
xform.eM11 = cosone;             //从Bitmap2反变换到Bitmap1
xform.eM12 = sinone;
xform.eM21 = -sinone;
xform.eM22 = cosone;
xform.eDx = (float)(cenx - cenx * cosone + ceny * sinone); //旋转中心
xform.eDy = (float)(ceny - ceny * cosone - cenx * sinone);
SetWorldTransform(bitmap2 -> Canvas -> Handle, &xform);
BitBlt(bitmap2 -> Canvas -> Handle,           //从Bitmap1搬迁数据到Bitmap2
       0,
       0,
       bitmap2 -> Width,
       bitmap2 -> Height,
       bitmap1 -> Canvas -> Handle,
       0,
       0,
       SRCCOPY);
Image2 -> Picture -> Bitmap = bitmap2;
//Image2 -> Left = (Image2 -> Width) / 2; //在Image2中居中显示
//Image2 -> Top = (Image2 -> Height) / 2;
delete bitmap1;
delete bitmap2;

xform.eDx = (float)(cenx - cenx * cosone + ceny * sinone); //旋转中心
xform.eDy = (float)(ceny - ceny * cosone - cenx * sinone);