add bouncing ball example (#6)

Added example with bouncing ball animation

Author: raidancampbell

examples/bouncing_ball.py

@@ -0,0 +1,83 @@
+import board
+import busio
+import adafruit_ssd1306
+
+# Create the I2C interface.
+i2c = busio.I2C(board.SCL, board.SDA)
+
+# Create the SSD1306 OLED class.
+# The first two parameters are the pixel width and pixel height.  Change these
+# to the right size for your display!
+oled = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c)
+
+
+# Helper function to draw a circle from a given position with a given radius
+# This is an implementation of the midpoint circle algorithm,
+# see https://en.wikipedia.org/wiki/Midpoint_circle_algorithm#C_example for details
+def draw_circle(xpos0, ypos0, rad, col=1):
+    x = rad - 1
+    y = 0
+    dx = 1
+    dy = 1
+    err = dx - (rad << 1)
+    while x >= y:
+        oled.pixel(xpos0 + x, ypos0 + y, col)
+        oled.pixel(xpos0 + y, ypos0 + x, col)
+        oled.pixel(xpos0 - y, ypos0 + x, col)
+        oled.pixel(xpos0 - x, ypos0 + y, col)
+        oled.pixel(xpos0 - x, ypos0 - y, col)
+        oled.pixel(xpos0 - y, ypos0 - x, col)
+        oled.pixel(xpos0 + y, ypos0 - x, col)
+        oled.pixel(xpos0 + x, ypos0 - y, col)
+        if err <= 0:
+            y += 1
+            err += dy
+            dy += 2
+        if err > 0:
+            x -= 1
+            dx += 2
+            err += dx - (rad << 1)
+
+# initial center of the circle
+center_x = 63
+center_y = 15
+# how fast does it move in each direction
+x_inc = 1
+y_inc = 1
+# what is the starting radius of the circle
+radius = 8
+
+# start with a blank screen
+oled.fill(0)
+# we just blanked the framebuffer. to push the framebuffer onto the display, we call show()
+oled.show()
+while True:
+    # undraw the previous circle
+    draw_circle(center_x, center_y, radius, col=0)
+
+    # if bouncing off right
+    if center_x + radius >= oled.width:
+        # start moving to the left
+        x_inc = -1
+    # if bouncing off left
+    elif center_x - radius < 0:
+        # start moving to the right
+        x_inc = 1
+
+    # if bouncing off top
+    if center_y + radius >= oled.height:
+        # start moving down
+        y_inc = -1
+    # if bouncing off bottom
+    elif center_y - radius < 0:
+        # start moving up
+        y_inc = 1
+
+    # go more in the current direction
+    center_x += x_inc
+    center_y += y_inc
+
+    # draw the new circle
+    draw_circle(center_x, center_y, radius)
+    # show all the changes we just made
+    oled.show()