2D Polygon Collision Detection

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;

namespace PolygonIntersection {

	public partial class MainForm : Form {

		List<Polygon> polygons = new List<Polygon>();
		Polygon player;

		public MainForm() {
			InitializeComponent();

			Paint += new PaintEventHandler(Form1_Paint);
			KeyDown += new KeyEventHandler(Form1_KeyDown);

			KeyPreview = true;
			DoubleBuffered = true;

			Polygon p = new Polygon();
			p.Points.Add(new Vector(100, 0));
			p.Points.Add(new Vector(150, 50));
			p.Points.Add(new Vector(100, 150));
			p.Points.Add(new Vector(0, 100));

			polygons.Add(p);

			p = new Polygon();
			p.Points.Add(new Vector(50, 50));
			p.Points.Add(new Vector(100, 0));
			p.Points.Add(new Vector(150, 150));
			p.Offset(80, 80);

			polygons.Add(p);			

			p = new Polygon();
			p.Points.Add(new Vector(0, 50));
			p.Points.Add(new Vector(50,0));
			p.Points.Add(new Vector(150,80));
			p.Points.Add(new Vector(160,200));
			p.Points.Add(new Vector(-10, 190));
			p.Offset(300, 300);
			
			polygons.Add(p);

			foreach (Polygon polygon in polygons) polygon.BuildEdges();

			player = polygons[0];
		}

		void Form1_Paint(object sender, PaintEventArgs e) {
			Vector p1;
			Vector p2;
			foreach (Polygon polygon in polygons) {
				for (int i = 0; i < polygon.Points.Count; i++) {
					p1 = polygon.Points[i];
					if (i + 1 >= polygon.Points.Count) {
						p2 = polygon.Points[0];
					} else {
						p2 = polygon.Points[i + 1];
					}
					e.Graphics.DrawLine(new Pen(Color.Black), p1, p2);
				}
			}

			Invalidate();
		}

		void Form1_KeyDown(object sender, KeyEventArgs e) {
			int i = 14;
			Vector velocity = new Vector();

			switch (e.KeyValue) {

				case 32: //SPACE

					break;

				case 38: // UP

					velocity = new Vector(0, -i);
					break;

				case 40: // DOWN

					velocity = new Vector(0, i);
					break;

				case 39: // RIGHT

					velocity = new Vector(i, 0);
					break;

				case 37: // LEFT

					velocity = new Vector(-i, 0);
					break;

			}

			Vector playerTranslation = velocity;

			foreach (Polygon polygon in polygons) {
				if (polygon == player) continue;

				PolygonCollisionResult r = PolygonCollision(player, polygon, velocity);

				if (r.WillIntersect) {
					playerTranslation = velocity + r.MinimumTranslationVector;
					break;
				}
			}

			player.Offset(playerTranslation);
			
		}

	}

}