Week 12: Interface Programming

In this section, we play with TKinter to do some graphics and show the coin detection! Neil's starter code shows us a bunch of moving boxes that display the raw data that is coming in from the board. But we can present it in a cleaner format, and it will let me learn how exactly the graphics pipeline works in python.

In the end, we manage to turn from the three-box setup at the top of the page, to the Moriya Shrine Donation Tracker directly above. I'll mostly go over the code in snippets and explain what each part does, since there wasn't much physical work to do in this week.

    from Tkinter import *
    WINDOW = 600 # window size

    root = Tk()
    root.title('Moriya Shrine Donation Tracker')
    canvas = Canvas(root, width=WINDOW, height=.65*WINDOW, background='white')
This first part basically sets up our environment. We import the Tkinter library, and then create an instance of the Tk object which acts as a general controller. We can give the wnidow a title and a size, as well as a background color.

    canvas.create_text(0.5*WINDOW, 0.03*WINDOW, text="Moriya Shrine Donation Tracker", font=("Helvetica", 24), fill="#0000b0")
    canvas.create_rectangle(.25*WINDOW,.25*WINDOW,.3*WINDOW,.3*WINDOW, tags='rect1_diff', fill='#b00000')
    canvas.create_rectangle(.3*WINDOW,.25*WINDOW,.9*WINDOW,.3*WINDOW, tags='rect2_diff', fill='#0000b0')
    canvas.create_text(.5*WINDOW,.225*WINDOW,text=".33",font=("Helvetica", 24),tags="text_diff",fill="#0000b0")
    canvas.create_text(.5*WINDOW,.325*WINDOW,text=".33",font=("Helvetica", 24),tags="text_avg",fill="#0000b0")
    canvas.create_text(.5*WINDOW,.425*WINDOW,text=".33",font=("Helvetica", 24),tags="text_dist",fill="#0000b0")
    canvas.create_text(.5*WINDOW,.525*WINDOW,text=".33",font=("Helvetica", 24),tags="text_bool",fill="#0000b0")
Next, we setup the GUI elements. Create_text makes a simple text box to display whatever string we want. Create_rectangle makes the red and blue boxes we saw earlier. The colors here are specified in hex values: basically, hexadecimal numbers that denote the colors as R,G,B values, with the first two bits for R, then for G and B.

Finally, canvas.pack() tells the window manager to compress its size to include the GUI elements we have just defined.

This little bit of code is what lets us inject logic into our GUI. After defining the GUI elements, we still want them to update in real-time. What Tkinter does is let us define an update function, in our case a function called 'idle', that gets called every 100ms or so. We can put whatever update logic we want in here -- such as reading from the serial and changing the text.

    def idle(parent,canvas):
       canvas.itemconfigure("text_diff",text="Current Difference: %.1f"%filter)
       canvas.itemconfigure("text_avg",text="Average Difference: %.1f"%currav)
       canvas.itemconfigure("text_dist",text="Distance from Avg: %.1f"%dist)
       canvas.itemconfigure("text_bool",text="No Coin Detected")
       if coincount > 0:
          canvas.itemconfigure("text_bool",text="Coin Detected!!!!!!1")
This is the core content of the update function I'm using. When we created the GUI elements a few blocks ago, we gave each one of them a tag, such as "text_diff" or "text_avg". This lets us refer to them in the update function with itemconfigure, allowing us to change the text content dynamically. We're doing the same thing with the rectangles, using canvas.coords to change the coordinates and size of the rectangle to reflect whatever value we want to show.