判断点在直线的哪个区域

bool pt_in_positive(CvPoint pt,CvPoint input_pt1,CvPoint input_pt2){double A,B,C;double k_t;k_t=input_pt2.x - input_pt1.x;if (k_t==0.){A=1;B=0;C=input_pt1.x;}else{double k,b;k=((double)input_pt2.y - input_pt1.y) /(input_pt2.x - input_pt1.x);b=input_pt1.y - k*input_pt1.x; A=k;B=-1;C=b;}if (A*pt.x+B*pt.y+C>0)return true;elsereturn false;}