From 8427b631e38567340818e4cd29dcfdfff63ae564 Mon Sep 17 00:00:00 2001
From: Pete Shadbolt <hello@peteshadbolt.co.uk>
Date: Mon, 8 Oct 2018 10:09:27 -0700
Subject: [PATCH] Messy

---
 verlet.py | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 verlet.py

diff --git a/verlet.py b/verlet.py
new file mode 100644
index 0000000..73c554b
--- /dev/null
+++ b/verlet.py
@@ -0,0 +1,73 @@
+"""
+Implements Verlet integration
+"""
+
+import pygame
+import numpy as np
+
+SIZE = (800, 800)
+CENTER = np.array(SIZE) / 2
+WHITE = (255, 255, 255)
+DAMPING = 0.99
+
+
+class Ball(object):
+    def __init__(self, x, y, radius=5, mass=1, fixed=False):
+        self.pos = np.array([x, y])
+        self.last_pos = np.array([x, y])
+        self.velocity = np.array([0., 0.])
+        self.radius = radius
+        self.mass = mass
+        self.fixed = fixed
+
+    def render(self, screen):
+        x, y = self.pos + CENTER
+        pygame.draw.circle(screen, WHITE, [int(x), int(y)], self.radius, 4)
+
+    def update(self):
+        if self.fixed:
+            return
+
+        # Gravity
+        #self.pos[1] += .05
+
+        # Bounce
+        if self.pos[1] > 400:
+            self.pos[1] = 400
+            self.last_pos[1] = 400
+            self.velocity[1] = -.5 * self.velocity[1]
+
+        self.pos += self.velocity
+
+        self.velocity = self.pos - self.last_pos
+        self.velocity *= DAMPING
+        self.last_pos = np.array(self.pos)
+
+
+class Spring(object):
+    def __init__(self, a, b, length=None, k=0.3):
+        self.a = a
+        self.b = b
+        self.k = k
+        self.length = self.compute_length() if length is None else length
+        print(self.length)
+
+    def render(self, screen):
+        x1, y1 = self.a.pos + CENTER
+        x2, y2 = self.b.pos + CENTER
+        pygame.draw.line(screen, WHITE, [x1, y1], [x2, y2])
+
+    def compute_length(self):
+        x1, y1 = self.a.pos + CENTER
+        x2, y2 = self.b.pos + CENTER
+        return np.sqrt((x2 - x1)**2 + (y2 - y1)**2)
+
+    def update(self):
+        current_length = self.compute_length()
+        delta = self.b.pos - self.a.pos
+        delta /= current_length
+        stretch = (current_length - self.length) / self.length
+        self.a.velocity += stretch * delta * self.k
+        self.b.velocity -= stretch * delta * self.k
+
+