Add example of Missile Command style missiles

examples/basic/missiles.py

@@ -0,0 +1,78 @@
+import random
+from collections import deque
+from itertools import tee
+from math import sin
+WIDTH = 800
+HEIGHT = 400
+
+GRAVITY = 5
+TRAIL_LENGTH = 400
+
+TRAIL_BRIGHTNESS = 100
+FLARE_COLOR = (255, 220, 160)
+
+missiles = []
+
+
+class Missile:
+    def __init__(self, x, vx, y=0, vy=20):
+        self.x = x
+        self.y = y
+        self.vx = vx
+        self.vy = vy
+        self.trail = deque(maxlen=TRAIL_LENGTH)
+        self.t = random.uniform(0, 3)
+
+    def step(self, dt):
+        self.t += dt
+        uy = self.vy
+        self.vy += GRAVITY * dt
+        self.y += 0.5 * (uy + self.vy) * dt
+
+        self.x += self.vx * dt
+        self.trail.appendleft((self.x, self.y))
+
+        # If the trail is off the bottom of the screen, kill the missile
+        if self.trail[-1][1] > HEIGHT:
+            missiles.remove(self)
+            return
+
+    def draw(self):
+        for i in range(len(self.trail)):
+            if i + 1 == len(self.trail):
+                break
+            start = self.trail[i]
+            end = self.trail[i + 1]
+            c = TRAIL_BRIGHTNESS * (1.0 - i / TRAIL_LENGTH)
+            color = (c, c, c)
+            screen.draw.line(start, end, color)
+        screen.draw.filled_circle((self.x, self.y), 2, FLARE_COLOR)
+
+        # This small flickering lens flare makes it look like the
+        # missile's exhaust is very bright.
+        flare_length = 4 + sin(self.t) * 2 + sin(self.t * 5) * 1
+        screen.draw.line(
+            (self.x - flare_length, self.y),
+            (self.x + flare_length, self.y),
+            FLARE_COLOR
+        )
+
+
+def draw():
+    screen.clear()
+    for m in missiles:
+        m.draw()
+
+
+def update(dt):
+    for m in list(missiles):
+        m.step(dt)
+
+
+def new_missile():
+    m = Missile(x=random.randrange(600, 800), vx=random.uniform(-70, -10))
+    missiles.append(m)
+
+
+new_missile()
+clock.schedule_interval(new_missile, 5)