add rainbow example

micropython/examples/gfx_pack/rainbow.py

@@ -0,0 +1,53 @@
+# This example borrows a CircuitPython hsv_to_rgb function to cycle through some rainbows on GFX Pack's screen.
+# If you're into rainbows, HSV (Hue, Saturation, Value) is very useful!
+
+import time
+from picographics import PicoGraphics, DISPLAY_GFX_PACK
+from gfx_pack import GfxPack
+
+display = PicoGraphics(display=DISPLAY_GFX_PACK, rotate=0)
+
+WIDTH, HEIGHT = display.get_bounds()
+
+gp = GfxPack()
+
+
+# From CPython Lib/colorsys.py
+def hsv_to_rgb(h, s, v):
+    if s == 0.0:
+        return v, v, v
+    i = int(h * 6.0)
+    f = (h * 6.0) - i
+    p = v * (1.0 - s)
+    q = v * (1.0 - s * f)
+    t = v * (1.0 - s * (1.0 - f))
+    i = i % 6
+    if i == 0:
+        return v, t, p
+    if i == 1:
+        return q, v, p
+    if i == 2:
+        return p, v, t
+    if i == 3:
+        return p, q, v
+    if i == 4:
+        return t, p, v
+    if i == 5:
+        return v, p, q
+
+
+h = 0
+display.set_font("bitmap8")
+
+while True:
+    h += 1
+    r, g, b = [int(255 * c) for c in hsv_to_rgb(h / 360.0, 1.0, 1.0)]  # rainbow magic
+    gp.set_backlight(r, g, b, 0)  # Set backlight to a converted HSV value
+    display.set_pen(15)           # Set pen to black
+    display.clear()
+    display.set_pen(0)            # Set pen to white
+    display.text("pico disco!", 18, 5, WIDTH, 2)   # Add some text
+    display.text("\\o/ \\o/ \\o/", 14, 25, WIDTH, 2)  # and some more text
+    display.text("\\o/ \\o/ \\o/", 14, 45, WIDTH, 2)  # and a bit more text
+    display.update()              # Update the display
+    time.sleep(1.0 / 60)