keypress.py

"""
Key press acquisition and interpretation. 
This module is closely bound to the view 
component. If a different view component is used, 
a corresponding keypress module must be used 
with it.  For example, we could have a pure textual
"glass tty" interface using curses, and in that case 
we would need to use curses functions to obtain keystrokes. 

"""

import sys
import graphics

# Internal codes for commands. 

LEFT = "Left"
RIGHT = "Right"
UP = "Up"
DOWN = "Down"
UNMAPPED = "Unmapped"
CLOSE = "Close"    # When the window is closed


# We can bind different areas of the keyboard to the
# commands. "Left", "right", etc are Tk codes for the
# arrow keys.  "jil," are a similar spatial pattern under
# the right hand. 
KEY_BINDINGS = { # Arrow keys, as interpreted by Tk and graphics.py
                 "Left": LEFT, "Right": RIGHT, "Up": UP, "Down": DOWN,
                 # left-hand --- some people use this pattern?
                 "a": LEFT, "w": UP, "s": RIGHT, "z": DOWN, 
                 # VI / Vim editor movement
                 "h": LEFT, "j": DOWN, "k": UP, "l": RIGHT,
                 # Numeric keypad (one common mapping)
                 "4": LEFT, "6": RIGHT, "8": UP, "2": DOWN
                 }


class Command(object):
    """Interpret keyboard input as commands from the 
    set LEFT, RIGHT, UP, DOWN, and UNMAPPED for a 
    key that does not have a binding. 
    """

    def __init__(self, game_view):
        self.game_view = game_view

    def next(self):
        try:
            key = self.game_view.get_key()
            if key not in KEY_BINDINGS:
                return UNMAPPED
            else:
                return KEY_BINDINGS[key]
        except graphics.graphics.GraphicsError as e:
            # This happens when the close button is pressed.
            if self.game_view.win.isClosed():
                return CLOSE
            raise e