# in_class.py
#
# demo done in class of a program
# that draws the graph of a function
# using Zelle's graphics API
#
# Jim M, Sep 2011

from graphics import *
from math import *

def main():

    # define some parameters
    windowWidth = 400     # in pixels
    windowHeight = 300
    xMin = 0.0
    xMax = 10.0
    yMin = -1.5
    yMax = 1.5
    xBorder = 1.0        # in x,y coordinates
    yBorder = 0.2
    nSteps = 200
    function = "sin(x)"

    # set up the win
    window = GraphWin("Function Plot", windowWidth, windowHeight)
    window.setCoords(xMin - xBorder, yMin - yBorder,
                     xMax + xBorder, yMax + yBorder)

    plotRectangle = Rectangle(Point(xMin,yMin),
                              Point(xMax,yMax))
    plotRectangle.setOutline("grey")
    plotRectangle.draw(window)

    # draw the function
    dx = (xMax - xMin)/nSteps
    x = xMin
    for i in range(nSteps):
        # draw a line from x to (x+dx)
        (x1, y1) = (x, eval(function))
        x = x + dx
        (x2, y2) = (x, eval(function))
        Line(Point(x1, y1), Point(x2, y2)).draw(window)

    # wait for the user to quit
    user_input = raw_input("Type <return> to quit. ")
    window.close()



main()