PlotDevice is designed to output PDF documents, images, and movies. In general it makes the trade-off of output quality over realtime responsiveness. If you’re looking to make something with low-latency interactivity (or other general whizzy-ness) you’re probably better off with a tool like NodeBox for OpenGL or Processing.

However, if you do want to experiment with interactivity in PlotDevice, there’s some built-in support that might be of help to you. This assumes you already know how to make an animation in PlotDevice.

Interacting with the mouse

In a PlotDevice animation, there are three predefined variables that store the current position of the mouse cursor and the state of the mouse button:

• MOUSEX: the horizontal location of the mouse cursor
• MOUSEY: the vertical location of the mouse cursor
• mousedown: is True when the mouse button is pressed, False otherwise

You would typically use the mousedown variable in an if-statement:

if mousedown:
     # do stuff when the mouse is pressed
else:
     # do stuff when the mouse isn't pressed

Interacting with the keyboard

Three predefined variables store the keys a user is pressing during a PlotDevice animation:

• key: the last key pressed
• keycode: the integer keycode of the last key pressed
• keydown: is True when a key is being pressed, False otherwise

The key and keycode variables are updated as long as any key is being pressed.

KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT contain the keycodes for the arrow keys and the delete key is represented by KEY_BACKSPACE.

Example

A fun example is this little sketch application. It builds up a list of points you’ve clicked-and-dragged over then draws a smooth bezier path connecting the vertices at every frame.

size(400 ,400)
speed(30)

def setup(anim):
    anim.path = []

def draw(anim):
    nofill()
    stroke(0)

    if mousedown:
        pt = Point(MOUSEX, MOUSEY)
        anim.path.append(pt)

    if anim.path:
        bezier(anim.path, smooth=True)