Dealing with mouse events
When we draw in a paint program, we use a mouse as the primary input device. There are primarily two kinds of mouse events that cause changes on the drawing canvas and are therefore of main interest:
Click and release
Click, drag, and release
There is also a third event in which we have limited interest—the mouse motion with no buttons clicked. Our interest is limited there since an unclicked motion normally does not cause any changes on the canvas.
We ignore right-click and wheel-scroll as we will not be using them in our program.
In both the preceding cases, we need to know where the mouse was first clicked and where it was released. For click and release this could be the same location. For click, drag, and release this will normally be different locations.
Accordingly, we define four attributes to keep track of the coordinates for these two locations (see code 6.02.py):
start_x, start_y = 0, 0
end_x, end_y = 0, 0Our immediate goal then is to bind our mouse...
