Create balls_demo.py example (#98)

This is adapted from the demo.py in the examples/pico_display directory.
It now displays full screen on a Pico Explorer

micropython/examples/pico_explorer/balls_demo.py

@@ -0,0 +1,66 @@
+# adapted from demo.py in examples/pico_display
+# runs full screen on a pico explorer
+# all credit to orignal author(s) - 
+# I just changed the import statement to import picoexplorer instaead of picodisplay
+
+
+import time, random
+import picoexplorer as display 
+
+width = display.get_width()
+height = display.get_height()
+
+display_buffer = bytearray(width * height * 2)  # 2-bytes per pixel (RGB565)
+display.init(display_buffer)
+
+#  display.set_backlight(1.0)
+
+
+class Ball:
+    def __init__(self, x, y, r, dx, dy, pen):
+        self.x = x
+        self.y = y
+        self.r = r
+        self.dx = dx
+        self.dy = dy
+        self.pen = pen
+
+# initialise shapes
+balls = []
+for i in range(0, 100):
+    r = random.randint(0, 10) + 3
+    balls.append(
+        Ball(
+            random.randint(r, r + (width - 2 * r)),
+            random.randint(r, r + (height - 2 * r)),
+            r,
+            (14 - r) / 2,
+            (14 - r) / 2,
+            display.create_pen(random.randint(0, 255), random.randint(0, 255), random.randint(0, 255)),            
+        )
+    )
+    
+while True:
+    display.set_pen(40, 40, 40)
+    display.clear()
+    
+    for ball in balls:
+        ball.x += ball.dx
+        ball.y += ball.dy
+        
+        xmax = width - ball.r
+        xmin = ball.r
+        ymax = height - ball.r
+        ymin = ball.r
+
+        if ball.x < xmin or ball.x > xmax:
+            ball.dx *= -1
+
+        if ball.y < ymin or ball.y > ymax:
+            ball.dy *= -1
+
+        display.set_pen(ball.pen)
+        display.circle(int(ball.x), int(ball.y), int(ball.r))
+        
+    display.update()
+time.sleep(0.01)