Selection area is not showing up in Tkinter

Question

I am developing an application which lets user Zoom a part of the graph based on their selection. I am able to get the initial x, y coordinates(x0, y0) and also

Answer 1

It works for me:

from Tkinter import *
from matplotlib.figure import *
import matplotlib

matplotlib.use('TkAgg')
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg

root = Tk()
graph = Figure(figsize=(5,4), dpi=100)
ax = graph.add_subplot(111)
plot = ax.plot([1,2,3,4],[5,6,2,8])
canvas = FigureCanvasTkAgg(graph, master=root)
canvas.show()
canvas.get_tk_widget().grid(column=2, row=1, rowspan=2, sticky=(N, S, E, W))

class Zoom(object):
    def __init__(self):
        self.graph = Figure(figsize=(5,4), dpi=100)
        self.ax = graph.add_subplot(111)

        # should be Rectangle((0,0),0,0)
        self.rect = Rectangle((10,10),100,100)
        self.ax.add_patch(self.rect)

        self.ax.plot([1,2,3,4],[5,6,2,8])
        self.is_pressed = False
        self.x0 = 0.0
        self.y0 = 0.0
        self.x1 = 0.0
        self.y1 = 0.0
        self.aid = graph.canvas.mpl_connect('button_press_event', self.on_press)
        self.bid = graph.canvas.mpl_connect('button_release_event', self.on_release)
        self.cid = graph.canvas.mpl_connect('motion_notify_event', self.on_motion)

    def on_press(self, event):
        self.is_pressed = True
        if event.xdata is not None and event.ydata is not None:
            self.x0, self.y0 = event.xdata, event.ydata

            print 'press:', self.x0, self.y0

            # only remove old rectangle
            self.rect.set_width(0)
            self.rect.set_height(0)
            self.rect.set_xy((self.x0, self.y0))
            self.ax.figure.canvas.draw()

            # color and linestyle for future motion 
            self.rect.set_facecolor('red')
            self.rect.set_linestyle('dashed')

    def on_motion(self, event):
        if self.is_pressed:
            if event.xdata is not None and event.ydata is not None:
                self.x1, self.y1 = event.xdata, event.ydata
                self.rect.set_width(self.x1 - self.x0)
                self.rect.set_height(self.y1 - self.y0)
                self.rect.set_xy((self.x0, self.y0))
                self.ax.figure.canvas.draw()
                print 'rect:', self.x0, self.y0, self.x1, self.y1, (self.x1-self.x0), (self.y1-self.y0)

    def on_release(self, event):
        self.is_pressed = False
        print 'release:', event.xdata, event.ydata

        # change only color and linestyle

        #self.rect.set_width(self.x1 - self.x0)
        #self.rect.set_height(self.y1 - self.y0)
        #self.rect.set_xy((self.x0, self.y0))

        self.rect.set_facecolor('blue')
        self.rect.set_linestyle('solid')
        self.ax.figure.canvas.draw()

my_object = Zoom()
root.mainloop()

Answer 2

You need to update these as the event changes:

def on_motion(self, event):
    if self.is_pressed is True:
        self.x1 = event.xdata
        self.y1 = event.ydata
        self.rect.set_width(1)
        self.rect.set_height(1)
        self.rect.set_xy((2.5, 5))
        self.rect.set_linestyle('dashed')
        self.ax.figure.canvas.draw()

def on_release(self, event):
    print 'release'
    self.is_pressed = False
    self.x1 = event.xdata
    self.y1 = event.ydata
    self.rect.set_width(1)
    self.rect.set_height(1)
    self.rect.set_xy((2.5, 5))
    self.rect.set_linestyle('solid')
    self.ax.figure.canvas.draw()

As is they will continually draw a fixed size rectangle at the coordinates (2.5, 5) with a width and height of 1.

Similar to the question you were looking at something like this works.

    def on_press(self, event):
        print('press')
        self.is_pressed = True
        self.x0 = event.xdata
        self.y0 = event.ydata

    def on_motion(self, event):
        self.x1, self.y1 = event.xdata, event.ydata
        if (self.is_pressed is True and
                self.x1 is not None and
                self.y1 is not None):
            self.rect.set_width(self.x1 - self.x0)
            self.rect.set_height(self.y1 - self.y0)
            self.rect.set_xy((self.x0, self.y0))
            self.rect.set_linestyle('dashed')
            self.ax.figure.canvas.draw()

    def on_release(self, event):
        print('release')
        self.is_pressed = False
        self.x1, self.y1 = event.xdata, event.ydata
        try:
            self.rect.set_width(self.x1 - self.x0)
            self.rect.set_height(self.y1 - self.y0)
            self.rect.set_xy((self.x0, self.y0))
        except TypeError:
            if (self.x1 is None or self.y1 is None):
                return
            else:
                raise
        self.rect.set_linestyle('solid')
        self.ax.figure.canvas.draw()

Notice that the rectangle dimensions are taken from the event. I added the guard to prevent mishaps where the event does not properly interpret the coordinate.

---

@furas makes a good points in the comments, it is a good idea to initialize your coordinates to floats.

    self.x0 = 0.0
    self.y0 = 0.0
    self.x1 = 0.0
    self.y1 = 0.0