推导：
x=rcos(b);
y=rsin(b);________(1)
x’=rcos(a+b);
y’=rsin(a+b);________(2)
cos(a+b)=cos(a)cos(b)-sin(a)sin(b);
sin(a+b)=sin(a)cos(b)+cos(a)sin(b);________(3)
将（3）代入（2）：
x’=rcos(a)cos(b)-rsin(a)sin(b);
y’=rsin(a)cos(b)+rcos(a)sin(b);________(4)
将（1）代入（4）：
x’=xcos(a)-ysin(a);
y’=xsin(a)+ycos(a);________(5)
根据（5）求对应源坐标：
x=x’cos(a)+y’sin(a);
y=-x’sin(a)+y’cos(a);
代码：
BYTE* Rotate(BYTE* pSrc,BYTE* pDest,int nWidth,int nHeight,int& nResW,int& nResH,double dAngel)
{
double cos_angle = cos(dAngel);
double sin_angle = sin(dAngel);
POINT p1={0,0};
POINT p2={nWidth,0};
POINT p3={0,nHeight};
POINT p4={nWidth,nHeight};
POINTF newP1,newP2,newP3,newP4, leftTop, rightTop, leftBottom, rightBottom;
newP1.x = (float)p1.x;
newP1.y = (float)p1.y;
newP2.x = (float)(p2.x*cos_angle - p2.y*sin_angle);
newP2.y = (float)(p2.x*sin_angle + p2.y*cos_angle);
newP3.x = (float)(p3.x*cos_angle - p3.y*sin_angle);
newP3.y = (float)(p3.x*sin_angle + p3.y*cos_angle);
newP4.x = (float)(p4.x*cos_angle - p4.y*sin_angle);
newP4.y = (float)(p4.x*sin_angle + p4.y*cos_angle);
leftTop.x = min(min(newP1.x,newP2.x),min(newP3.x,newP4.x));
leftTop.y = min(min(newP1.y,newP2.y),min(newP3.y,newP4.y));
rightBottom.x = max(max(newP1.x,newP2.x),max(newP3.x,newP4.x));
rightBottom.y = max(max(newP1.y,newP2.y),max(newP3.y,newP4.y));
leftBottom.x = leftTop.x;
leftBottom.y = rightBottom.y;
rightTop.x = rightBottom.x;
rightTop.y = leftTop.y;
nResW = (int) floor(0.5f + rightTop.x - leftTop.x);
nResH= (int) floor(0.5f + leftBottom.y - leftTop.y);
BYTE* pRet = new BYTE[nResW*nResH*3];
int nOldStride = nWidth*3;
int nNewStride = nResW*3;
int x,y,newX,newY,oldX,oldY;
for (y = (int)leftTop.y, newY = 0; y<=(int)leftBottom.y; y++,newY++)
{
int nNewPosY = newY*nNewStride;
for (x = (int)leftTop.x, newX = 0; x<=(int)rightTop.x; x++,newX++)
{
oldX = (int)(x*cos_angle + y*sin_angle + 0.5);
oldY = (int)(y*cos_angle - x*sin_angle + 0.5);
if(IsPointInside(oldX,oldY,nWidth,nHeight))
{
int nNewPosX = newX*3;
int nOldPos = oldY*nOldStride + oldX*3;
if (nOldPos >= 0)
{
pRet[nNewPosY + nNewPosX] = pSrc[nOldPos];
pRet[nNewPosY + nNewPosX + 1] = pSrc[nOldPos + 1];
pRet[nNewPosY + nNewPosX + 2] = pSrc[nOldPos + 2];
}
}
}
}
return pRet;
}
