CS21: Lab 11

You may work with one partner on this assignment

Run update21, if you haven't already, to create the cs21/labs/11 directory. Then cd into your cs21/labs/11 directory and create the python programs for lab 11 in this directory.

$ update21
$ cd cs21/labs/11
$ vim grid.py

Introduction

For this assignment, you will write two classes, Cell and Grid, and then write a program that uses these classes to draw a picture to the graphics window. The Cell and Grid classes are designed to be used by programs that implement time-step simulations of some phenomena on a 2-D world. Simulating heat dissipation over a sheet of metal or an insect infestation on a crop of wheat, or even climate modeling are examples of such discrete time-step simulations. In these types of simulations, the world is broken up into a grid of cells, where each cell summarizes the information for its part of the world. At each discrete time step, a cell's value changes based on some function that involves its neighboring cell's values. So, in the insect model, if a neighboring cell is infested, it is likely that in a few time steps the cell will become infested too, and after some more time, when the insects have eaten all the wheat in that cell, they will move on. In the next lab assignment, you will use the Cell and Grid classes to implement a simulation program like one of these.

In this assignment you will use the graphics library to draw the world represented by a Grid object that contains a list of lists of Cell objects. For our implementation a Cell can have one of two values (ON and OFF) and you will color cells differently based on their current value. Once you have the Cell and Grid classes implemented you will write a program that uses them to draw a pixelated picture to the graphics window, by setting Cells values to ON or OFF.

Cell class

The cell class represents 1 square unit in a 2-D grid in the Graphics window. A Cell object has some some state including:

its row and column position in the 2-D grid,
it current value (ON or OFF)
its value for the next time step (ON or OFF)
its Rectangle object

In addition, all Cell objects share the same definitions for ON and OFF and their associated colors (the Cell should be colored one color if its value is ON, another if its value is OFF).

A Cell has the following methods:

constructor (just the __init__ method) that takes a row, column, and value and creates a new Rectangle object at that position
getRow(): returns the value of the row field
getColumn(): returns the value of the column field
getValue(): returns the value of the value field
getRectangle(): returns a reference to its rectangle field
setNextValue(val): set the Cell's next value to val
update(): change a Cell's value to its next value and update its color

Grid class

The Grid class is used to represent the world. It has some state:

number of rows and columns in the world
a GraphWin object
a list of lists of Cell objects, one for each (row, column) element in the world. The outer list is indexed by row number to get an inner list that contains all Cells in the row (one for each column in the grid)

For a grid with 4 rows and 2 columns, your list of lists of Cell objects will look like this:

			[ [r0c0,r0c1], [r1c0,r1c1], [r2c0,r2c1], [r3c0,r3c1]  ]

where r0c0 is the cell object in row 0,column 0; and r2c1 is the cell object in row 2,column 1.

The Grid has the following methods:

constructor: takes the number of rows and columns and creates a new graphics window. It also creates a list of lists of Cell objects and draws each Cell to the graphics window (use the Cell's getRectangle method to get a reference to the Rectangle object associated with the cell so that you can invoke its draw method)
numRows(): returns the number of rows in the grid
numCols(): returns the number of columns in the grid
getValue(row, col): returns the value of the cell at (row, col)
setNextValue(row, col, val): sets the next value of the cell at (row,col)
update(): simulates a time step (each Cell's value should be updated to its next value)
close(): prompt the user to click to close the graphics window

Using these classes

At the bottom of the grid.py file that contains the Cell and Grid class definitions, add a main function that will create a new Grid object and then call its methods to draw a pixelated picture to the graphics window by setting Cell to ON or OFF. You could draw a smiley face, your initials, a house, anything you'd like.

For example, here is a run of my program that creates a 15 by 15 grid and draws my initials to it (notice that I have an option to "click to close" so that the program doesn't exit until the user is done viewing it):

$ python grid
click to close

You do not have to use these classes to draw your initials, but use them to draw something that is a bit more complicated than a single line. You can hard-code in the row and column dimensions for the grid for your drawing.

Hints/Getting Started

The syntax for starting a class definition and its constructor (remember that data member fields need to be prefixed with self. so that python can distinguish between them and local variables):

class Cell(object):

    # any class-wide definitions go go here
    # these are fields that are associated with the class as a whole
    # their values that can be accessed using 
    # <name of class>.<name_of_field>  (ex) x = Cell.ON
    ON = 1

    # This is the constructor for a Cell object.  Remember that all
    # method functions have a 1st hidden parameter, self, that is
    # a reference to the object on which the method is invoked.
    # A call to this method might look like:  c = Cell(3,4,Cell.ON)
    def __init__(self, row, col, val):

    # here is an example of what other method definitions might look like
    # a call to this might look like:  c.foo(Cell.OFF)
    def foo(self, val)
        row = self.row  # row is a local variable inside this method
                        # self.row is a data member associated with this object

Use the setCoords method of the GraphWin class to set the coordinate system to correspond to the number of rows and columns. setCoords(x1,y1,x2,y2) changes the coordinates in the Graphics window from individual pixel values, to a larger coordinate system where (x1,y1) is in the lower-left corner and (x2,y2) is in the upper right corner. So, in the constructor of the Grid class, I might set the coordinate system by doing the following (win is the Grid data member that refers to the GraphWin object):
```
 self.win.setCoords(0, 0, cols, rows)
```
By doing this I can position Cell objects using their (row, column) index, rather than having to perform a conversion from row number to pixel row value and column number to pixel column value.
Cell objects should be stored by the Grid class as a list of lists of Cells. Here is how I could add the first two rows of 3 cells each to the cell list of lists (of course you should generalize this and put the code in loops so that it will work for any number of rows and columns):
```
self.cell_list = []
self.cell_list.append( [Cell(0,0,Cell.OFF), Cell(0,1,Cell.OFF), Cell(0,2,Cell.OFF)])
self.cell_list.append([Cell(1,0,Cell.OFF), Cell(1,1,Cell.OFF), Cell(1,2,Cell.OFF)])
```
You can access the Cell object in row r and column c by indexing cell_list with its row number, r, to get the correct row list, and then indexing into that list with its col number, c, to get the correct Cell object in the correct column position:
```
cell = self.cell_list[r][c]
	
```

Optional Extensions

These are not required, so do not try these until you have the basic assignment complete and correct. Here are some extensions you can try:

Animate your drawing in some way. You can do this by repeatedly
1. setting some Cells' next value to ON or OFF
2. calling update
3. calling the sleep function to sleep some number of tenths of a second
```
 from time import sleep
```
Generalize your drawing into a function, and implement it so that what is drawn shows up as roughly the same size and at the same position in the graphics window no matter the dimensions of the Grid. For example, if the Grid has 20x20 cells then you will have to color more cells to draw your picture than if it has 10x10 cells.

Submit

Once you are satisfied with your program, hand it in by typing handin21 in a terminal window.

CS21 Lab 11: Grid and Cell Classes