Add particles example

examples/basic/particles.py

@@ -0,0 +1,51 @@
+import random
+import math
+
+
+WIDTH = 800
+HEIGHT = 600
+
+DRAG = 0.8  # fraction of speed lost per second
+PARTICLE_COLOR = 255, 230, 128
+MAX_AGE = 3
+
+particles = []
+
+def explode(x, y, speed=300):
+    age = 0
+    for _ in range(100):
+        angle = random.uniform(0, math.tau)
+        radius = random.uniform(0, 1) ** 0.5
+
+        vx = speed * radius * math.sin(angle)
+        vy = speed * radius * math.cos(angle)
+        particles.append((x, y, vx, vy, age))
+
+
+def draw():
+    screen.clear()
+    for x, y, *_ in particles:
+        screen.surface.set_at((int(x), int(y)), PARTICLE_COLOR)
+
+
+def update(dt):
+    new_particles = []
+    for (x, y, vx, vy, age) in particles:
+        if age + dt > MAX_AGE:
+            continue
+        drag = DRAG ** dt
+        vx *= drag
+        vy *= drag
+        x += vx * dt
+        y += vy * dt
+        age += dt
+        new_particles.append((x, y, vx, vy, age))
+    particles[:] = new_particles
+
+
+def explode_random():
+    x = random.randrange(WIDTH)
+    y = random.randrange(HEIGHT)
+    explode(x, y)
+
+clock.schedule_interval(explode_random, 1.5)