2D polygon filling

//2D polygon filling (arbitrary poly; full and partial pixels are counted. handles slivers. x incremened ++)
//[email protected]

// old, untested code

#include <iostream>
#include <algorithm>
#include <cmath>
#include <map>
using namespace std;


#define MAX 100
#define X first
#define YY second
#define A first
#define B second
typedef pair<int,int> PII;
typedef pair<PII,PII> Seg;

pair<double,double> y[MAX];
int Y[MAX];
PII p[MAX];
Seg seg[MAX],li[MAX];
map<int,int> m;

int main() {
    int x, i, it, n, a, lin, lit, j, segn;
    Seg s, tmp;
    while ((cin >> n) && n) {
        for (i = 0; i < n; i++) cin >> p[i].first >> p[i].second;
        segn = 0;
        m.clear();
        for (i = j = 0; i < n; i++) {
            if (p[i].first == p[(i + 1) % n].first) continue;
            else if (p[i] < p[(i + 1) % n]) seg[j++] = (make_pair(p[i], p[(i + 1) % n]));
            else seg[j++] = (make_pair(p[(i + 1) % n], p[i]));
        }
        segn = j;
        sort(seg, seg + segn);
        a = 0;
        x = seg[0].first.first;
        it = 0;
        lin = 0;
        while (it < segn || lin) {
            for (i = 0, lit = 0; lit < lin; lit++, i++)
                y[i] = make_pair(li[lit].A.YY + (double)(li[lit].B.YY - li[lit].A.B)*(x - 1 - li[lit].A.X) / (double)(li[lit].B.X - li[lit].A.X),
                    li[lit].A.YY + (double)(li[lit].B.YY - li[lit].A.YY)*(x - li[lit].A.X) / (double)(li[lit].B.X - li[lit].A.X));
            n = i;
            sort(y, y + n);
            for (i = 0; i < n; i += 2) {
                Y[i + 1] = (int)(ceil(max(y[i + 1].first, y[i + 1].second)));
                Y[i] = floor(min(y[i].first, y[i].second));
            }
            for (i = 0; i < n; i += 2) {
                if (i && Y[i] < Y[i - 1]) Y[i] = Y[i - 1];
                if (Y[i + 1] < Y[i]) Y[i + 1] = Y[i];
                a += Y[i + 1] - Y[i];
            }
            if (m[x])
                for (i = 0; i < lin; )
                    if (li[i].second.first == x) swap(li[i], li[--lin], tmp);
                    else i++;
            while (it < segn && seg[it].first.first == x) {
                li[lin++] = seg[it];
                m[seg[it].second.first] = 1;
                it++;
            }
            x++;
        }
        cout << a << endl;
    }
    return 0;
}