Add Galaxian diving example

examples/basic/galaxian.py

@@ -0,0 +1,99 @@
+import math
+
+WIDTH = 400
+HEIGHT = 800
+
+# How many wobbles the ship does while diving
+DIVE_WOBBLE_SPEED = 2
+
+# How far the ship wobbles while diving
+DIVE_WOBBLE_AMOUNT = 100
+
+
+def dive_path(t):
+    """Get the ship's position at time t when diving.
+
+    This is relative to the ship's original position (so, at t=0, dive_path(t)
+    returns (0, 0)).
+
+    """
+    if t < 0.5:
+        # During the first 0.5s, do a half-loop
+        return (
+            50 * (1 - math.cos(2 * t * math.pi)),
+            -50 * (math.sin(2 * t * math.pi))
+        )
+
+    # For the rest of the time, follow a sinusoidal path downwards
+    t -= 0.5
+    return (
+        DIVE_WOBBLE_AMOUNT * math.cos(t * DIVE_WOBBLE_SPEED),
+        t * 350,
+    )
+
+
+def ship_controller_pan(ship, dt):
+    """Update the ship when the ship is panning."""
+    ship.x += ship.vx * dt
+    if ship.right > WIDTH - 50:
+        ship.vx = -ship.vx
+        ship.right = WIDTH - 50
+    elif ship.left < 50:
+        ship.vx = -ship.vx
+        ship.left = 50
+
+
+def ship_controller_dive(ship, dt):
+    """Update the ship when the ship is diving."""
+    # Move the ship along the path
+    ship.t += dt
+    divex, divey = dive_path(ship.t)
+    startx, starty = ship.dive_start
+    ship.pos = (startx + divex * ship.dive_dir, starty + divey)
+
+    # Look ahead along the path to see what direction the ship
+    # is moving, and set the ship's rotation accordingly
+    ex, ey = dive_path(ship.t + EPSILON)
+    ship.angle = math.degrees(math.atan2(
+        divey - ey,
+        (ex - divex) * ship.dive_dir
+    ))
+
+    # If we've reached the bottom of the screen, resume dive mode
+    if ship.top > HEIGHT:
+        ship.controller_function = ship_controller_pan
+        ship.pos = ship.dive_start
+        ship.angle = 90
+        clock.schedule(start_dive, 3)
+
+
+EPSILON = 0.001
+
+# Create a ship
+ship = Actor('ship', pos=(100, 100), angle=90)
+ship.angle = 90  # Face upwards
+ship.controller_function = ship_controller_pan
+ship.vx = 100
+
+
+def draw():
+    screen.clear()
+    ship.draw()
+
+
+def update(dt):
+    ship.controller_function(ship, dt)
+
+
+def start_dive():
+    ship.controller_function = ship_controller_dive
+    ship.dive_start = ship.pos
+    x, y = ship.pos
+    if ship.x < WIDTH // 2:
+        ship.dive_dir = 1
+    else:
+        ship.dive_dir = -1
+    ship.t = 0
+
+
+clock.schedule(start_dive, 3)