Creating stable image Python Arcade

Question

I am trying to write a program using the Python Arcade library where the user presses the spacebar causing a red circle to appear on the screen. However, whenever I press the spacebar, the image will appear, but it will flicker very rapidly, as if it is being drawn and erased and redrawn several times per second. I want to make it so after a spacebar press the circle will remain on the screen without this flickering. Below is the code which I was using.

import arcade

SCREEN_WIDTH = 600
SCREEN_HEIGHT = 600

class Ball:
    def __init__(self, x , y, radius, color):
        self.x = x
        self.y = y
        self.radius = radius
        self.color = color

    def draw(self):
        arcade.draw_circle_filled(self.x, self.y, self.radius, self.color)


class MyGame(arcade.Window):
    def __init__(self, width, height, title):
        super().__init__(width, height, title)

        arcade.set_background_color(arcade.color.ASH_GREY)

        self.ball=Ball(300, 300, 50, arcade.color.AUBURN)

        arcade.start_render()

    def on_key_press(self, key, modifiers):
        if key == arcade.key.SPACE:
            self.ball.draw()

def main():
    window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, "Press spacebar")
    arcade.run()

if __name__ == "__main__":
    main()

Answer 1

I do not have the arcade library installed but it appears to me you can simply use a tracking variable to check if you have already pressed spacebar.

class MyGame(arcade.Window):
    def __init__(self, width, height, title):
        super().__init__(width, height, title)
        self.first_press = False # added tracking variable

        arcade.set_background_color(arcade.color.ASH_GREY)

        self.ball=Ball(300, 300, 50, arcade.color.AUBURN)

        arcade.start_render()

    def on_key_press(self, key, modifiers):
        # added an "and" clause to the if statement to check tracking variable
        if key == arcade.key.SPACE and self.first_press == False:
            self.ball.draw()
            # with this change this if statement will no longer trigger after first press.
            self.first_press = True 

Answer 2

In my experience with Arcade, the place where you draw your circle is the def on_draw(self):. You put that in your MyGame Class and draw what you want in it after the arcade.start_render() (so this is where your self.ball.draw() goes). Since you want to make the object Ball appear on your screen you can create a trigger variable that will make it appear.

Here is an example of what it would look like based on your code:

import arcade

SCREEN_WIDTH = 600
SCREEN_HEIGHT = 600


class Ball:
    def __init__(self, x, y, radius, color):
        self.x = x
        self.y = y
        self.radius = radius
        self.color = color

    def draw(self):
        arcade.draw_circle_filled(self.x, self.y, self.radius, self.color)


class MyGame(arcade.Window):
    def __init__(self, width, height, title):
        super().__init__(width, height, title)

        arcade.set_background_color(arcade.color.ASH_GREY)

        self.ball = Ball(300, 300, 50, arcade.color.AUBURN)
        self.show_ball = False

        arcade.start_render()

    def on_draw(self):
        arcade.start_render()

        # will draw the ball if self.show_ball is True
        if self.show_ball:
            self.ball.draw()

    def on_key_press(self, key, modifiers):
        if key == arcade.key.SPACE:
            self.show_ball = True


def main():
    window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, "Press spacebar")
    arcade.run()


if __name__ == "__main__":
    main()

In my opinion, the usage of a dataclass could be interesting since the ball is basically just data and I think it would make it easier to read (I don't think it's a standard, it's just the way I learned it at school). With my suggestion, it would give you:

import arcade
from dataclasses import dataclass

SCREEN_WIDTH = 600
SCREEN_HEIGHT = 600

@dataclass
class Ball:
    x: int
    y: int
    radius: int
    color: (int, int, int)

    def draw(self):
        arcade.draw_circle_filled(self.x, self.y, self.radius, self.color)


class MyGame(arcade.Window):
    def __init__(self, width, height, title):
        super().__init__(width, height, title)

        arcade.set_background_color(arcade.color.ASH_GREY)

        self.ball = Ball(300, 300, 50, arcade.color.AUBURN)
        self.show_ball = False

        arcade.start_render()

    def on_draw(self):
        arcade.start_render()

        # will draw the ball if self.show_ball is True
        if self.show_ball:
            self.ball.draw()

    def on_key_press(self, key, modifiers):
        if key == arcade.key.SPACE:
            self.show_ball = True


def main():
    window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, "Press spacebar")
    arcade.run()


if __name__ == "__main__":
    main()

If you have any other questions about the arcade library feel free to ask the discord server (https://discord.gg/s4ctsYbC), they will be happy to help you.