计算[s,e]线段是否经过rc区域

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/计算[s,e]线段是否经过rc区域
BOOL isLineInRetc(const RECT rc, const POINT s, const POINT e)
{
  BOOL bRet = FALSE;

  //两点式计算与边界的交点
  // y = (y2-y1)/(x2-x1)*(x-x1) + y1;
  double x1 = s.x, y1 = s.y;
  double x2 = e.x, y2 = e.y;
  double fYL = (y2-y1)/(x2-x1)*(rc.left - x1) + y1;
  double fYR = (y2-y1)/(x2-x1)*(rc.right - x1) + y1;
  double fXT = (x2-x1)/(y2-y1)*(rc.top - y1) + x1;
  double fXB = (x2-x1)/(y2-y1)*(rc.bottom - y1) + x1;

  //RECT范围
  double fRMinx = rc.left;
  double fRMaxx = rc.right;
  double fRMiny = rc.top;
  double fRMaxy = rc.bottom;

  //线段范围
  double fLMiny = min(y1, y2);
  double fLMaxy = max(y1, y2);
  double fLMinx = min(x1, x2);
  double fLMaxx = max(x1, x2);

  if(s.x >= fRMinx && s.x <= fRMaxx && s.y >= fRMiny && s.y <= fRMaxy)
  {
    //起点在区域内?
    bRet |= 0x01;
  }
  if(e.x >= fRMinx && e.x <= fRMaxx && e.y >= fRMiny && e.y <= fRMaxy)     
  {
    //结束点在区域内?
    bRet |= 0x02;
  }
  
  //与左边界有交点 & 在线段内?
  if(fYL >= fLMiny && fYL <= fLMaxy && fYL >= fRMiny && fYL <= fRMaxy)
  {
    bRet |= 0x10;
  }

  //与右边界有交点 & 在线段内?
  if(fYR >= fLMiny && fYR <= fLMaxy && fYR >= fRMiny && fYR < fRMaxy)
  {
    bRet |= 0x20;
  }

  //与上边界有交点 & 在线段内?
  if(fXT >= fLMinx && fXT <= fLMaxx && fXT >= fRMinx && fXT <= fRMaxx)
  {
    bRet |= 0x40;
  }

  //与下边界有交点 & 在线段内?
  if(fXB >= fLMinx && fXB <= fLMaxx && fXB >= fRMinx && fXB <= fRMaxx)
  {
    bRet |= 0x80;
  }

  return bRet;
}