//-------------------------------------------------------calc_polygon_area
public static double calc_polygon_area(VertexSequence st)
{
int i;
double sum = 0.0;
double x = st[0].x;
double y = st[0].y;
double xs = x;
double ys = y;
for (i = 1; i < st.size(); i++)
{
VertexDistance v = st[i];
sum += x * v.y - y * v.x;
x = v.x;
y = v.y;
}
return((sum + x * ys - y * xs) * 0.5);
}
static public void shorten_path(VertexSequence vs, double s, int closed)
{
if (s > 0.0 && vs.size() > 1)
{
double d;
int n = (int)(vs.size() - 2);
while (n != 0)
{
d = vs[n].dist;
if (d > s)
{
break;
}
vs.RemoveLast();
s -= d;
--n;
}
if (vs.size() < 2)
{
vs.remove_all();
}
else
{
n = (int)vs.size() - 1;
VertexDistance prev = vs[n - 1];
VertexDistance last = vs[n];
d = (prev.dist - s) / prev.dist;
double x = prev.x + (last.x - prev.x) * d;
double y = prev.y + (last.y - prev.y) * d;
last.x = x;
last.y = y;
if (!prev.IsEqual(last))
{
vs.RemoveLast();
}
vs.close(closed != 0);
}
}
}
