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dastelsdastels
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Port from C and optimize
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‎examples/gravity/main.py

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import board
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import busio
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import math
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import random
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import adafruit_lsm303
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import adafruit_dotstar
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N_GRAINS = 10 # Number of grains of sand
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WIDTH = 12 # Display width in pixels
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HEIGHT = 6 # Display height in pixels
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NUMBER_PIXELS = WIDTH * HEIGHT
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MAX_FPS = 45 # Maximum redraw rate, frames/second
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GRAIN_COLOR = (64, 64, 64)
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MAX_X = WIDTH * 256 - 1
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MAX_Y = HEIGHT * 256 - 1
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class Grain:
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def __init__(self):
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x = 0
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y = 0
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vx = 0
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vy = 0
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grains = [Grain() for _ in range(N_GRAINS)]
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i2c = busio.I2C(board.SCL, board.SDA)
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sensor = adafruit_lsm303.LSM303(i2c)
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wing = adafruit_dotstar.DotStar(board.D13, board.D11, WIDTH * HEIGHT, 1.0, False)
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oldidx = 0
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newidx = 0
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delta = 0
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newx = 0
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newy = 0
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occupied_bits = [False for _ in range(WIDTH * HEIGHT)]
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def index_of_xy(x, y):
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return (y >> 8) * WIDTH + (x >> 8)
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def already_present(i, x, y):
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for j in range(i):
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if x == grains[j].x or y == grains[j].y:
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return True
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return False
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for g in grains:
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placed = False
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while not placed:
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g.x = random.randint(0, WIDTH * 256 - 1)
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g.y = random.randint(0, HEIGHT * 256 - 1)
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placed = not occupied_bits[index_of_xy(g.x, g.y)]
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occupied_bits[index_of_xy(g.x, g.y)] = True
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g.vx = 0
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g.vy = 0
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while True:
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# Display frame rendered on prior pass. It's done immediately after the
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# FPS sync (rather than after rendering) for consistent animation timing.
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for i in range(NUMBER_PIXELS):
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wing[i] = GRAIN_COLOR if occupied_bits[i] else (0,0,0)
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wing.show()
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# Read accelerometer...
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f_x, f_y, f_z = sensor.raw_accelerometer
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ax = f_x >> 8 # Transform accelerometer axes
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ay = f_y >> 8 # to grain coordinate space
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az = abs(f_z) >> 11 # Random motion factor
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az = 1 if (az >= 3) else (4 - az) # Clip & invert
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ax -= az # Subtract motion factor from X, Y
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ay -= az
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az2 = (az << 1) + 1 # Range of random motion to add back in
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# ...and apply 2D accel vector to grain velocities...
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v2 = 0 # Velocity squared
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v = 0.0 # Absolute velociy
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for g in grains:
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g.vx += ax + random.randint(0, az2) # A little randomness makes
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g.vy += ay + random.randint(0, az2) # tall stacks topple better!
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# Terminal velocity (in any direction) is 256 units -- equal to
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# 1 pixel -- which keeps moving grains from passing through each other
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# and other such mayhem. Though it takes some extra math, velocity is
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# clipped as a 2D vector (not separately-limited X & Y) so that
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# diagonal movement isn't faster
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v2 = g.vx * g.vx + g.vy * g.vy
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if v2 > 65536: # If v^2 > 65536, then v > 256
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v = math.floor(math.sqrt(v2)) # Velocity vector magnitude
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g.vx = (g.vx // v) << 8 # Maintain heading
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g.vy = (g.vy // v) << 8 # Limit magnitude
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# ...then update position of each grain, one at a time, checking for
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# collisions and having them react. This really seems like it shouldn't
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# work, as only one grain is considered at a time while the rest are
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# regarded as stationary. Yet this naive algorithm, taking many not-
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# technically-quite-correct steps, and repeated quickly enough,
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# visually integrates into something that somewhat resembles physics.
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# (I'd initially tried implementing this as a bunch of concurrent and
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# "realistic" elastic collisions among circular grains, but the
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# calculations and volument of code quickly got out of hand for both
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# the tiny 8-bit AVR microcontroller and my tiny dinosaur brain.)
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for g in grains:
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newx = g.x + g.vx # New position in grain space
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newy = g.y + g.vy
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if newx > MAX_X: # If grain would go out of bounds
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newx = MAX_X # keep it inside, and
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g.vx //= -2 # give a slight bounce off the wall
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elif newx < 0:
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newx = 0
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g.vx //= -2
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if newy > MAX_Y:
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newy = MAX_Y
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g.vy //= -2
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elif newy < 0:
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newy = 0
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g.vy //= -2
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oldidx = index_of_xy(g.x, g.y) # prior pixel
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newidx = index_of_xy(newx, newy) # new pixel
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if oldidx != newidx and occupied_bits[newidx]: # If grain is moving to a new pixel... but if that pixel is already occupied...
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delta = abs(newidx - oldidx) # What direction when blocked?
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if delta == 1: # 1 pixel left or right
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newx = g.x # cancel x motion
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g.vx //= -2 # and bounce X velocity (Y is ok)
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newidx = oldidx # no pixel change
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elif delta == WIDTH: # 1 pixel up or down
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newy = g.y # cancel Y motion
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g.vy //= -2 # and bounce Y velocity (X is ok)
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newidx = oldidx # no pixel change
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else: # Diagonal intersection is more tricky...
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# Try skidding along just one axis of motion if possible (start w/
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# faster axis). Because we've already established that diagonal
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# (both-axis) motion is occurring, moving on either axis alone WILL
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# change the pixel index, no need to check that again.
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if abs(g.vx) > abs(g.vy): # x axis is faster
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newidx = index_of_xy(newx, g.y)
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if not occupied_bits[newidx]: # that pixel is free, take it! But...
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newy = g.y # cancel Y motion
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g.vy //= -2 # and bounce Y velocity
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else: # X pixel is taken, so try Y...
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newidx = index_of_xy(g.x, newy)
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if not occupied_bits[newidx]: # Pixel is free, take it, but first...
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newx = g.x # Cancel X motion
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g.vx //= -2 # Bounce X velocity
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else: # both spots are occupied
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newx = g.x # Cancel X & Y motion
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newy = g.y
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g.vx //= -2 # Bounce X & Y velocity
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g.vy //= -2
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newidx = oldidx # Not moving
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else: # y axis is faster. start there
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newidx = index_of_xy(g.x, newy)
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if not occupied_bits[newidx]: # Pixel's free! Take it! But...
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newx = g.x # Cancel X motion
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g.vx //= -2 # Bounce X velocity
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else: # Y pixel is taken, so try X...
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newidx = index_of_xy(newx, g.y)
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if not occupied_bits[newidx]: # Pixel is free, take it, but first...
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newy = g.y # cancel Y motion
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g.vy //= -2 # and bounce Y velocity
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else: # both spots are occupied
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newx = g.x # Cancel X & Y motion
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newy = g.y
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g.vx //= -2 # Bounce X & Y velocity
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g.vy //= -2
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newidx = oldidx # Not moving
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occupied_bits[oldidx] = False
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occupied_bits[newidx] = True
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g.x = newx
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g.y = newy

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