From 7757f565bf0f7694c6de57a2795117521c92e5a7 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <Nat Lasseter nathan@bytemark.co.uk>
Date: Wed, 28 Jun 2017 21:11:50 +0100
Subject: Some bouncy lines

---
 particle.js | 20 ++++++++++++++++++--
 sketch.js   | 18 ++++++++++++++----
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/particle.js b/particle.js
index c62dd47..b6b116c 100644
--- a/particle.js
+++ b/particle.js
@@ -30,7 +30,23 @@ function Particle(x, y, m, c) {
     point(this.pos.x, this.pos.y);
   }
 
-  this.gone = function() {
-    return this.pos.y >= hei;
+  this.reflect = function(surface_vector, elastic_coeff) {
+    var normal = surface_vector
+                  .copy()
+                  .normalize()
+                  .rotate(PI/2);
+    this.vel = this.vel.sub(p5.Vector.mult(normal, 2 * this.vel.dot(normal))).mult(elastic_coeff);
+  }
+
+  this.online = function(x1, y1, x2, y2) {
+    var dist = function(x1, y1, x2, y2) {
+      return Math.sqrt(Math.pow(x1 - x2, 2) + Math.pow(y1 - y2, 2));
+    };
+
+    return Math.abs(
+        dist(x1, y1, this.pos.x, this.pos.y) +
+        dist(this.pos.x, this.pos.y, x2, y2) -
+        dist(x1, y1, x2, y2)
+      ) < 1;
   }
 }
diff --git a/sketch.js b/sketch.js
index 2c6b9d3..ce3d1d1 100644
--- a/sketch.js
+++ b/sketch.js
@@ -13,6 +13,11 @@ function setup() {
 function draw() {
   background(0);
 
+  stroke(255);
+  strokeWeight(4);
+  line(0, 0.75*hei, 0.25*wid, hei);
+  line(0.75*wid, hei, wid, 0.75*hei);
+
   for(var i = ps.length - 1; i >= 0; i--) {
     ps[i].applyForce(gravity);
     ps[i].applyDrag(air_resistance);
@@ -22,17 +27,22 @@ function draw() {
     strokeWeight(ps[i].mass);
     ps[i].show();
 
-    if (ps[i].gone()) {
-     ps.splice(i, 1);
+    if (ps[i].online(0, 0.75*hei, 0.25*wid, hei)) {
+      ps[i].reflect(createVector(0.25*wid, 0.25*hei), 5);
+    } else if (ps[i].online(0.75*wid, hei, wid, 0.75*hei)) {
+      ps[i].reflect(createVector(0.25*wid, -0.25*hei), 5);
     }
+
+    if (ps[i].pos.y >= hei)
+      ps.splice(i, 1);
   }
 
   if (mouseIsPressed) {
     var p = new Particle(
-          mouseX, mouseY, random(2, 8),
+          mouseX, mouseY, random(2, 10),
           color(random(0, 360), random(90, 100), random(50, 100))
         );
-    p.applyForce(createVector(random(-200, 200), random(-400, 0)));
+    p.applyForce(createVector(random(-250, 250), random(-500, 0)));
     ps.push(p);
   }
 }
-- 
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