学步园

1.原理

S=S1+S2+S3

S=三角片面积

Si判断点与三角片其中一条边组成的三角形

2.代码

#include <iostream><br /> #include <cmath><br /> using namespace std;<br /> double CrossArea(double x1, double y1, double x2, double y2, double x3, double y3)<br /> {<br /> double ax=x2-x1,ay=y2-y1,bx=x2-x3,by=y2-y3;<br /> return fabs(ax*by-ay*bx)/2;<br /> }<br /> bool judgePtInTriangle(double x1, double y1, double x2, double y2, double x3, double y3, double ptx, double pty)<br /> {<br /> double S = CrossArea(x1, y1, x2, y2, x3, y3);<br /> double S1 = CrossArea(x2, y2, x3, y3, ptx, pty);<br /> double S2 = CrossArea(x1, y1, x3, y3, ptx, pty);<br /> double S3 = CrossArea(x1, y1, x2, y2, ptx, pty);</p> <p> return fabs(S-S1-S2-S3)<0.000001;<br /> }<br /> int main()<br /> {<br /> //149805.173649<br /> printf("%f/n", CrossArea(392.273392, 66.604418, 1099.486314 ,1.744933, 559.373665 , 474.928843));<br /> cout << "judge" << endl;<br /> cout << judgePtInTriangle(392.273392, 66.604418, 1099.486314 ,1.744933, 559.373665 , 474.928843, 733.733258, 185.967057) << endl;<br /> cout << judgePtInTriangle(392.273392, 66.604418, 1099.486314 ,1.744933, 559.373665 , 474.928843, 955.076363, 383.956810) << endl;<br /> return 0;<br /> }