已知直线过两点，和线外一点，求直线和垂足及垂距

//直线过P1,P2两点，P0为直线外一点，求P0到直线的距离和P0在直线上的垂足
 
void HelloWorld::initPoint(cocos2d::CCPoint point0,cocos2d::CCPoint point1,cocos2d::CCPoint point2)
 
{
 
 P1 = point1; 
 //直线上的第一个点
 
 P2 = point2; 
 //直线上的第二个点
 
 P0 = point0; 
 //直线外的一点
 
}
 
//得到点到直线的距离
 
float HelloWorld::getLenthPointToLine()
 
{
 
 A = P2.y - P1.y;
 
 B = P1.x - P2.x;
 
 C = P1.y*(P2.x - P1.x) - P1.x*(P2.y - P1.y);
 
//直线为Ax+By+C=0
 
 CCLog("A = %f,B = %f,C = %f",A,B,C); 
 
   d = fabsf(A*P0.x+B*P0.y+C)/sqrt(A*A+B*B);
  
 CCLog("d = %f",d);
  
 return d;
  
}
  
//得到点在直线上的垂足
  
cocos2d::CCPoint HelloWorld::getPointToLineChuiZu()
  
{
  
 float D = A*P0.y - B*P0.x;
  
 float xd = -(B*D + A*C)/(B*B + A*A);
  
 

  float yd;
  
 if (B == 0)
  
 {
  
  yd = P0.y;
  
 }else{
  
  yd = -(A*xd+C)/B;
  
 }
  
 
  
 

   CCLog("c(%f,%f)",xd,yd);
 
 
 

   return ccp(xd,yd);
  
}