void myTriangle(double ox, double oy, double length)
{
double tmp0 = (sqrt(3)/3)*length;
double tmp1 = length/2;
double tmp2 = (sqrt(3)/6)*length;
double Ax = ox;
double Ay = oy + tmp0;
double Bx = ox - tmp1;
double By = oy - tmp2;
double Cx = ox + tmp1;
double Cy = By;

glBegin(GL_TRIANGLES);
glVertex2d(Ax, Ay);
glVertex2d(Bx, By);
glVertex2d(Cx, Cy);
glEnd();
}