function SameSide(p1,p2, a,b)
    cp1 = CrossProduct(b-a, p1-a)
    cp2 = CrossProduct(b-a, p2-a)
    if DotProduct(cp1, cp2) >= 0 then return true
    else return false

function PointInTriangle(p, a,b,c)
    if SameSide(p,a, b,c) and SameSide(p,b, a,c)
        and SameSide(p,c, a,b) then return true
    else return false

void myMouse(int button, int state, int x, int y)
{
   int sb;
   int s1, s2, s3;
   int x1=100, y1=100, x2=130, y2=220, x3=200, y3=60;
   
   y=480-y;

   sb=fabs((x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2))/2);
   s1=fabs((x1*(y2-y)+x2*(y-y1)+x*(y1-y2))/2);
   s2=fabs((x2*(y3-y)+x3*(y-y2)+x*(y2-y3))/2);
   s3=fabs((x3*(y1-y)+x1*(y-y3)+x*(y3-y1))/2);
   
   if(button==GLUT_LEFT_BUTTON && state==GLUT_DOWN && sb==(s1+s2+s3))
      kvadrat(x2,y2);
   if(button==GLUT_LEFT_BUTTON && state==GLUT_DOWN && sb!=(s1+s2+s3))
      myDisplay();
}