CPSC120B
Fundamentals of Computer Science

Mouse Input

• Graphics module has functions for getting mouse and keyboard input

• The ‘wait’ function are blocking functions, the program stops running until user input

  gaphics.wait_for_button_press()
  graphics.draw_oval(0, 0, 100, 100, fill="black")

• Can also get the current mouse state

  graphics.mouse_x()
  graphics.mouse_y()

• But this isn’t useful unless repeatedly checking the value inside of a loop

  for i in range(100):
      x = graphics.mouse_x()
      y = graphics.mouse_y()
      graphics.clear()
      graphics.draw_oval(x, y, 100, 100, fill="black")
      graphics.wait()

• This runs a fixed number of frames, it would be better to run as long as the user wants

  while graphics.window_open():
      x = graphics.mouse_x()
      y = graphics.mouse_y()
      graphics.clear()
      graphics.draw_oval(x, y, 100, 100, fill="black")
      graphics.wait()

• Can also get the button state

  x = 0
  y = 0
  while graphics.window_open():
      if graphics.button_down(1):
          x = graphics.mouse_x()
          y = graphics.mouse_y()
      graphics.clear()
      graphics.draw_oval(x, y, 100, 100, fill="black")
      graphics.wait()

• The 1 argument to the button_down function tests if the left mouse button is down

Keyboard Input

• Like mouse input, there are blocking and non-blocking keyboard input functions

• The blocking functions stop the program until the user presses or releases a key

  graphics.wait_for_key_press()
  graphics.draw_oval(0, 0, 100, 100, fill="black")

• To get keyboard input in a program that uses a loop to create animations, use the non-blocking functions

  while graphics.window_open():
      graphics.clear()
      if graphics.key_down('space'):
          graphics.draw_oval(x, y, 100, 100, fill="black")
      graphics.wait()

Image Velocity

• To create images that can change direction, need to store the direction the image is moving in variables
• This is the velocity of the image, the number of pixels it moves in the x and y direction each frame of animation

• The oval in the following example moves 2 pixels right and 1 pixel down every frame of animation

  x = 0
  y = 0
  x_velocity = 2
  y_velocity = 1
  while graphics.window_open():
      x = graphics.mouse_x()
      y = graphics.mouse_y()
      graphics.clear()
      graphics.draw_oval(x, y, 100, 100, fill="black")
      graphics.wait()

• Change x_velocity and y_velocity to change the direction and speed of the circle

• Can get the circle to ‘bounce’ off of the edges of the window by computing new velocity when it hits an edge

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