Add example file for plotting lines

Thanks to s-light for originally contributing this!

Author: tekktrik

examples/displayio_cartesian_lineplot.py

@@ -0,0 +1,63 @@
+# SPDX-FileCopyrightText: 2021 Stefan Krüger
+#
+# SPDX-License-Identifier: MIT
+#############################
+"""
+This is a basic demonstration of a Cartesian widget for line-ploting
+"""
+
+import time
+import board
+import displayio
+from adafruit_displayio_layout.widgets.cartesian import Cartesian
+
+# create the display on the PyPortal or Clue or PyBadge(for example)
+display = board.DISPLAY
+# otherwise change this to setup the display
+# for display chip driver and pinout you have (e.g. ILI9341)
+
+# pybadge display:  160x128
+# Create a Cartesian widget
+# https://circuitpython.readthedocs.io/projects/displayio-layout/en/latest/api.html#module-adafruit_displayio_layout.widgets.cartesian
+my_plane = Cartesian(
+    x=15,  # x position for the plane
+    y=2,  # y plane position
+    width=140,  # display width
+    height=105,  # display height
+    xrange=(0, 10),  # x range
+    yrange=(0, 10),  # y range
+)
+
+my_group = displayio.Group()
+my_group.append(my_plane)
+display.show(my_group)  # add high level Group to the display
+
+data = [
+    # (0, 0),  # we do this point manually - so we have no wait...
+    (1, 1),
+    (2, 1),
+    (2, 2),
+    (3, 3),
+    (4, 3),
+    (4, 4),
+    (5, 5),
+    (6, 5),
+    (6, 6),
+    (7, 7),
+    (8, 7),
+    (8, 8),
+    (9, 9),
+    (10, 9),
+    (10, 10),
+]
+
+print("examples/displayio_layout_cartesian_lineplot.py")
+
+# first point without a wait.
+my_plane.add_plot_line(0, 0)
+for x, y in data:
+    my_plane.add_plot_line(x, y)
+    time.sleep(0.5)
+
+while True:
+    pass