How to make a tkinter canvas rectangle transparent?

Question

I need to make my tkinter rectangles transparent. Does anyone know how to do that?

I have tried to specify alpha=".5", opacity=".5", and I have tried to add two more digits in the end of the color code: fill="#ff000066". None of these things seem to work, I can't find the right syntax.

import tkinter

root = tkinter.Tk()
canvas = tkinter.Canvas(root, width=800, height=600)
canvas.pack()

canvas.create_rectangle(50, 50, 100, 100, fill="#ff0000", alpha=0.5)

root.mainloop()

This code gives me this message: _tkinter.TclError: unknown option "-alpha", so this is obviously not the right way to do it.

Answer 1

You can use transparent image to simulate the result. Use Pillow to create transparent image and then use canvas.create_image(...) to draw it. Below is a sample code:

from tkinter import *
from PIL import Image, ImageTk

root = Tk()

images = []  # to hold the newly created image

def create_rectangle(x1, y1, x2, y2, **kwargs):
    if 'alpha' in kwargs:
        alpha = int(kwargs.pop('alpha') * 255)
        fill = kwargs.pop('fill')
        fill = root.winfo_rgb(fill) + (alpha,)
        image = Image.new('RGBA', (x2-x1, y2-y1), fill)
        images.append(ImageTk.PhotoImage(image))
        canvas.create_image(x1, y1, image=images[-1], anchor='nw')
    canvas.create_rectangle(x1, y1, x2, y2, **kwargs)

canvas = Canvas(width=300, height=200)
canvas.pack()

create_rectangle(10, 10, 200, 100, fill='blue')
create_rectangle(50, 50, 250, 150, fill='green', alpha=.5)
create_rectangle(80, 80, 150, 120, fill='#800000', alpha=.8)

root.mainloop()

And the output:

Answer 2

In a canvas if you want some widget to be transparent, simply let the fill parameter be empty:

fill=""