arrows.py

# arrows.py
# Walker M. White (wmw2)
# November 17, 2014
"""Module to show off how to use the keyboard.

This module is like animation.py, except that it looks at the key presses
to perform the animation."""
import colormodel
import random
import math
from game2d import *


############# CONSTANTS #############
# Window Size
WINDOW_WIDTH  = 512
WINDOW_HEIGHT = 512

# Distance from Window Center
ANIMATION_RADIUS = 100
# AMOUNT TO CHANGE THE ANGLE
ANIMATION_STEP   = 0.1
# Ellipse Radius
ELLIPSE_RADIUS = 20


############# CONTROLLER CLASS #############
class Arrows(GameApp):
    """Instance is an application to animate an ellipse about a center.
    
    At each step, the update() method looks at the key presses.  If neither
    the left nor right arrow is pressed, nothing happens.  Otherwise, it
    computes a new angle in the appropriate direction.  It finds the (x,y)
    coordinate that corresponds to the polar coordinate (ANIMATION_RADIUS,angle)
    and puts the ellipse there.
    
    Instance Attributes (Not hiding any):
        view  [GView]: the view (inherited from Game) 
        angle [float]: ellipse angle from center 
        ellipse [GEllipse, center is (RADIUS,self.angle) in polar coords]: 
            the ellipse to animate 
    """
    
    # THE THREE MAIN METHODS
    def start(self):
        """Initializes application, creating new attributes."""
        self.angle = 0
        pos=self._polar_to_coord(ANIMATION_RADIUS,self.angle)
        self.ellipse = GEllipse(x=pos[0],y=pos[1],
                                width=ELLIPSE_RADIUS,height=ELLIPSE_RADIUS,
                                fillcolor=colormodel.RED)
    
    def update(self,dt):
        """Animates the ellipse.
        
        Parameter dt: The time since the last animation frame.
        Precondition: dt is a float."""
        # Look at the key presses
        # Doing this way cause left and right to cancel each other out
        da = 0
        if self.input.is_key_down('left'):
            da += ANIMATION_STEP
        if self.input.is_key_down('right'):
            da -= ANIMATION_STEP
        
        # Change the angle
        self.angle = self.angle+da % (2*math.pi)
        pos=self._polar_to_coord(ANIMATION_RADIUS,self.angle)
        self.ellipse.x = pos[0]
        self.ellipse.y = pos[1]
    
    def draw(self):
        """Draws the ellipse"""
        self.ellipse.draw(self.view)
    
    
    # HELPER METHOD
    def _polar_to_coord(self,r,a):
        """Returns: Tuple (x,y) equal to polar coord (r,a)"""
        return (r*math.cos(a)+self.width/2.0,r*math.sin(a)+self.height/2.0)


# Application Code
if __name__ == '__main__':
    Arrows(width=WINDOW_WIDTH,height=WINDOW_HEIGHT,fps=60.0).run()