PythonGraphicsIntro

1. Python Graphics Introduction

This page describes using Tkinter (a graphics interface) in Python.

1.1. Starting Tkinter

You start Tkinter by importing it in python:

>>> import Tkinter

1.2. Create a Window

You can create a basic window with:

>>> win = Tkinter.Tk()

1.3. Add a Canvas

A canvas is a place to draw. This adds a canvas to the window.

>>> can = Tkinter.Canvas(win, width=500, height=500, background='white')
>>> can.pack()

You must always "pack" an object before you can see it.

1.4. Putting things on the Canvas

In Tkinter, you don't actually "draw" on the canvas, but you put objects onto the canvas. That means that you can move the things once they are there, and each object has properties that it can take care of (such as handling mouse events, moving itself, etc).

>>> can.create_rectangle(10, 10, 30, 40, width = 0, tag = "label", fill = "red")
>>> can.create_line(5, 10, 60, 90, fill = "blue")
>>> can.create_text(10, 70, text='Hello World!', fill='black')
>>> can.create_oval(10, 10, 70, 70)

Each of those commands return an object ID (we just ignored the return value, though). X and Y start at 0,0 in the upper left-hand corner and increase on the canvas as you go right and down, respectively.

Each object can have an associated "tag" which can be used to get a handle on the graphic object, so that you can move or delete it:

>>> can.create_rectangle(10, 10, 30, 40, width = 0, tag = "label", fill = "red")
>>> id = can.create_line(5, 10, 60, 90, fill = "blue")
>>> can.delete( "label" )                # deletes all with same tag
>>> can.delete(id)                       # deletes by ID
>>> canvas.delete("all")                 # deletes everything

Programmatically, you can display the window, and allow mouse events by:

>>> win.mainloop()

1.5. Some miscellaneous things

You can put a title on the window with:

win.wm_title("Title of my Window")

Some simple code for adding a button that draws on a canvas. randomLine.py:

import Tkinter, random
 
def redraw():
    r1 = random.random() * 200
    r2 = random.random() * 200
    r3 = random.random() * 200
    r4 = random.random() * 200
    canvas.create_line(r1, r2, r3, r4)
 
win = Tkinter.Tk()
 
canvas = Tkinter.Canvas(win, 100, 200) ## 100 x 200 width x height
canvas.pack()
 
button = Tkinter.Button(win, text = "Push me!", command = redraw)
button.pack()

Either add a call to win.mainloop() or call with python -i randomLine.py.

A better design might involve packaging up the above code as a class, randomLineClass.py.

import Tkinter, random
                                                                                                 
class Lines:
    def __init__(self):
        self.win = Tkinter.Tk()
                                                                                                 
        self.canvas = Tkinter.Canvas(self.win, 100, 200)
        self.canvas.pack()
                                                                                                 
        self.button = Tkinter.Button(self.win, text = "Push me!", command = self.redraw)
        self.button.pack()
                                                                                                 
     def redraw(self):
        r1 = random.random() * 200
        r2 = random.random() * 200
        r3 = random.random() * 200
        r4 = random.random() * 200
        self.canvas.create_line(r1, r2, r3, r4, fill = "red", outline = "yellow")
                                                                                                 
lineObject = Lines()

But what if you want to be drawing, and be able to handle mouse clicks on buttons at the same time? That will require a little bit more complication...

2. An Extended Example

This example takes in an image, looks for Black, Red, and White regions, and makes a matrix with the values 0, .5, and 1 for those colors, respectively.

Here is a sample image:

Here is the code.

# An extended example to get an image,
# convert to a matrix form, and change
# via clicking
# D.S. Blank
 
import Tkinter, sys
 
class Display(Tkinter.Toplevel):
    def __init__(self, root, filename):
        Tkinter.Toplevel.__init__(self, root)
        self.image = Tkinter.PhotoImage(file=filename)
        self.protocol('WM_DELETE_WINDOW',self.destroy)
        self.frame = Tkinter.Frame(self)
        self.canvas = Tkinter.Canvas(self.frame, width = 100, height = 100)
        self.canvas.create_image(0, 0, image = self.image, anchor=Tkinter.NW,
                                 tag="image")
        self.canvas.bind("<Button-1>", self.click)
        self.frame.pack()
        self.canvas.pack()
        self.makeMatrix()
 
    def destroy(self):
        sys.exit(1)
 
    def makeMatrix(self):
        # make a 2D matrix:
        self.cell = [[0 for x in range(100)] for y in range(100)]
        # fill it with pixel values:
        for x in range(100):
            for y in range(100):
                r, g, b = map(int, self.image.get(x, y).split(" "))
                if (r, g, b) == (255, 0, 0): # red:
                    self.cell[x][y] = .5
                elif (r, g, b) == (255, 255, 255): # white
                    self.cell[x][y] = 1
                elif (r, g, b) == (0, 0, 0): # black
                    self.cell[x][y] = 0
 
    def click(self, event):
        # Get the click location:
        x, y = event.x, event.y
        # get Red, Green, Blue:
        r, g, b = map(int, self.image.get(x, y).split(" "))
        print "Click at (%d, %d) = (%d, %d, %d)" % (x, y, r, g, b)
        print "Cell[%d][%d] = %.1f" % (x, y, self.cell[x][y])
        # white is 255, 255, 255
        # red is 255, 0, 0
        # black is 0, 0, 0
 
if __name__ == "__main__":
    root = Tkinter.Tk()
    root.withdraw()
    display = Display(root, "butterfly.gif")
    display.mainloop()

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Immutable page (last modified 2006-03-12 22:02:31)

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