Add in initial work on Pong tutorial.

.gitignore

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+.idea/

DEV_NOTES.md

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+# Notes while working on Kivy
+
+## Tutorial Improvements:
+- [Adding Ball Animation](https://kivy.org/docs/tutorials/pong.html#adding-ball-animation)
+    - Add in placeholder variable to describe the random direction of the ball.
+
+## Kivy File
+- Properties need to be declared at the top of a section in Kv.
+- Nothing in the Kv language specification on the order of properties / sections.
+
+## Kivy language
+- [Documentation for Kv language](https://kivy.org/docs/guide/lang.html)
+- Documentation on language does not have an explicit section on adding comments.
+- Nice to have tips for syntax-highlighting inside Kv files for PyCharm.

main.py

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+import random
+
+from kivy import app, clock, properties, vector
+from kivy.uix import widget
+
+
+class PongGame(widget.Widget):
+    # ADD note: why the None needed... the API allows for *args, **kwargs
+    ball = properties.ObjectProperty(None)
+
+    def serve_ball(self):
+        self.ball.center = self.center
+        # NOTE: Breaking this out
+        random_ball_direction = random.randint(0, 360)
+        self.ball.velocity = vector.Vector(4, 0).rotate(random_ball_direction)
+
+    def update(self, dt):
+        self.ball.move()
+
+        # bounce off top and bottom
+        if (self.ball.y < 0) or (self.ball.top > self.height):
+            self.ball.velocity_y *= -1
+
+        # bounce off left and right
+        if (self.ball.x < 0) or (self.ball.right > self.width):
+            self.ball.velocity_x *= -1
+
+
+class PongBall(widget.Widget):
+    velocity_x = properties.NumericProperty(0)
+    velocity_y = properties.NumericProperty(0)
+
+    velocity = properties.ReferenceListProperty(velocity_x, velocity_y)
+
+    def move(self):
+        self.pos = vector.Vector(*self.velocity) + self.pos
+
+
+class PongApp(app.App):
+
+    def build(self):
+        game = PongGame()
+        game.serve_ball()
+        clock.Clock.schedule_interval(game.update, 1.0 / 60.0)
+        return game
+
+
+def run_pong_game():
+    PongApp().run()
+
+
+if __name__ == '__main__':
+    run_pong_game()

pong.kv

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+#:kivy 1.0.9
+
+<PongGame>:
+    # This needs to be up top, otherwise the properties are not defined.
+    ball: pong_ball
+
+    canvas:
+        Rectangle:
+            pos: self.center_x - 5, 0
+            size: 10, self.height
+
+    Label:
+        font_size: 70
+        center_x: root.width / 4
+        top: root.top - 50
+        text: "0"
+
+    Label:
+        font_size: 70
+        center_x: root.width * 3 / 4
+        top: root.top - 50
+        text: "0"
+
+    PongBall:
+        id: pong_ball
+        center: self.parent.center
+
+<PongBall>:
+    size: 50, 50
+    canvas:
+        Ellipse:
+            pos: self.pos
+            size: self.size