Minesweeper in Matplotlib
Lately I've been playing around with interactivity in matplotlib. A couple weeks ago, I discussed briefly how to use event callbacks to implement simple 3D visualization and later used this as a base for creating a working 3D Rubik's cube entirely in matplotlib.
Today I have a different goal: re-create minesweeper, that ubiquitous single-player puzzle game that most of us will admit to having binged on at least once or twice in their lives. In minesweeper, the goal is to discover and avoid hidden mines within a gridded minefield, and the process takes some logic and quick thinking.
To implement this in matplotlib, at its most stripped-down level, simply requires us to register mouse clicks on the plot window, and to have the window respond in the appropriate way. The rest is just the logic underneath.
Matplotlib contains several built-in event callbacks. You can register
key presses (with
mouse clicks (with
mouse movement (with
'motion_notify_event'), and much more. For
a full listing of the events that can be bound to functionality, see the
documentation of the function
As a simple example, here we'll create a polygon and a function which is called
each time the axis is clicked. The function
on_click checks if the click
occured within the polygon, and if so changes the polygon to a random
import numpy as np import matplotlib.pyplot as plt fig = plt.figure() ax = fig.add_subplot(111, xlim=(-1, 2), ylim=(-1, 2)) polygon = plt.Polygon([[0, 0], [1, 0], [1, 1], [0, 1], [0, 0]]) ax.add_patch(polygon) # Function to be called when mouse is clicked def on_click(event): if polygon.contains_point((event.x, event.y)): polygon.set_facecolor(np.random.random(3)) fig.canvas.draw() # Connect the click function to the button press event fig.canvas.mpl_connect('button_press_event', on_click) plt.show()
The result will look something like this:
Checking whether a click event is within a polygon or any other artist is
a very common pattern. For this reason, matplotlib provides a built-in
pick event. You can think of this as an event similar to a mouse click,
but specifically generated by a plot artist when it is clicked.
pick event is associated back to that particular plot
element, which can be easily referenced within the callback.
Here is a code snippet which gives is equivalent to the code above,
but uses pick events rather than button press events:
import numpy as np import matplotlib.pyplot as plt fig = plt.figure() ax = fig.add_subplot(111, xlim=(-1, 2), ylim=(-1, 2)) polygon = plt.Polygon([[0, 0], [1, 0], [1, 1], [0, 1], [0, 0]]) ax.add_patch(polygon) # set the picker to True, so that pick events are registered polygon.set_picker(True) # create a function to be bound to pick events: here the event has an # attribute `artist` which points to the object which was clicked def on_pick(event): event.artist.set_facecolor(np.random.random(3)) fig.canvas.draw() # bind pick events to our on_pick function fig.canvas.mpl_connect('pick_event', on_pick) plt.show()
Here we have used just a single polygon, but there's nothing to stop us from using multiple interactive polygons in a single window. Add some logic beneath it all, and the results can be extremely flexible. We'll go through one in-depth example below.
Using this simple machinery, let's create a basic implementation of the game Minesweeper. This involves creating a grid of polygons, with a certain number of them "containing" mines. Clicking the left mouse button will "uncover" the square, ending the game if a mine is underneath. If (as we'd hope) an uncovered square does not contain a mine, it will reveal a number reporting how many of the eight adjacent squares contain mines. The right mouse button is used to mark where we believe mines are.
There are some other more sophisticated features in the below code -- for example, clicking an already uncovered square with the correct number of adjacent mines marked will automatically clear the surrounding squares -- but rather than enumerating every programming decision, I'll just show you the code. It's less than 200 lines, but the results are pretty nice:
There are still some things missing from this which are present in any good minesweeper implementation: a timer, the ability to reset the game without restarting the program, the ability to keep track of fastest times, and likely some more things I haven't thought of.
Regardless, this little script shows how incredibly powerful a framework matplotlib is. It can create an interactive Rubik's cube one day, publication-quality plots the next, and round out the season with a blast back to a classic Windows 3.1 time-sink. And for some reason, I find I have much more fun playing the minesweeper I built from scratch than the one that came with my system.