playing with palette animation in CircuitPython

beachball_bounce.py

# beachball_bounce.py -- playing with palette animation
# 29 Mar 2022 - @todbot / Tod Kurt
# Tested on ESP32-S2 Feather, but doesn't require it
# Needs "pinwheel_30.bmp", a 30x30 8-color pinwheel, where color0 is background
# created with ImageMagick:
#  convert pinwheel.png -resize 30x30 -colors 8 -type palette -compress None BMP3:pinwheel_30.bmp
import time
import board
import displayio
import random

display = board.DISPLAY
display.auto_refresh=True

maingroup = displayio.Group()
display.show(maingroup) # put main group on display, everything goes in maingroup

yaccel = 0.1
yaccel_max = 3.2
num_balls = 5
ball_w = 30 

balls = [None] * num_balls # holds the ball Tile_Grid objects w/ x,y
ball_pos =  [(0,0,0,0,)] * num_balls  # holds ball position & acceleration (xvel, yvel, xaccel, yaccel) 

for i in range(num_balls):
    # bmp balls
    bitmap = displayio.OnDiskBitmap(open("/pinwheel_30.bmp", "rb"))
    pal = bitmap.pixel_shader
    pal.make_transparent(0)
    balls[i] = displayio.TileGrid(bitmap, pixel_shader=pal)
    ball_pos[i] = (30,30, 1+random.random()*3, random.random()*3 )
    maingroup.append(balls[i])

def rotate_palette(pal):
    tmp = pal[7]  # save topmost color
    for i in range(8, 0, -1):
        pal[i+1] = pal[i] # move all colors up
    pal[1] = tmp  # add back saved color (pal[0] is transparent)
    
last_weird_time = time.monotonic()
while True:
    for i in range(num_balls):
        (x,y,xvel,yvel) = ball_pos[i]
        x = x + xvel 
        y = y + yvel
        yvel = min(yvel + yaccel, yaccel_max)  # add "gravity"
        # if we hit an edge, bounce & change color!
        if x < 0 or x > (display.width - ball_w):
            xvel = -xvel
            yvel = yvel - yaccel_max/2  # add a little spice
        if y > (display.height - ball_w):
            yvel = -yvel
  
        balls[i].x = int(x)
        balls[i].y = int(y)
        ball_pos[i] = (x,y,xvel,yvel)  # save position & velocity for next time
        
    if time.monotonic() - last_weird_time > 0.1:
        last_weird_time = time.monotonic()
        for i in range(num_balls):
            rotate_palette( balls[i].pixel_shader )
        
    display.refresh( target_frames_per_second = 60 )
    time.sleep(0.001)

The image used