(Solved) window resizable and grab_set causes white flicker when using dark mode

[ageekhere]

Hi, I been having an issue with a white flicker when creating a new window whilst using dark mode. If i use

new_window.resizable(False, False) # Stop user from resizing the window
new_window.grab_set() # Make new window be on top of main window

I will get a quick white flash when opening the window.

Example code

import customtkinter
def open_new_window():
    new_window = customtkinter.CTkToplevel(app)

    new_window.resizable(False, False)
    new_window.grab_set()
    
    new_window.title("New Window")
    new_window.geometry("1000x800")
    # Create a CTk button with functionality inside the new window
    close_button1 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button2 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button3 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button4 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button5 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button6 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button7 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button8 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button9 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button10 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
    close_button1.pack()
    close_button2.pack()
    close_button3.pack()
    close_button4.pack()
    close_button5.pack()
    close_button6.pack()
    close_button7.pack()
    close_button8.pack()
    close_button9.pack()
    close_button10.pack()

# Main CTk window
app = customtkinter.CTk()
app.geometry("1000x800")
customtkinter.set_appearance_mode("dark")  # Set dark theme

# Main window button with command to open the new window
main_button = customtkinter.CTkButton(app, text="Open New Window", command=open_new_window)
main_button.pack()

# Start the main event loop
app.mainloop()

python version 3.12.4
customtkinter 5.2.2

[dipeshSam]

@ageekhere
In your case, main problem is in the .resizable(False, False). This function triggers new windowingsystem. Give it some time to update the background color as default color in Tkinter is somehow white. In the following way, there would be NO white flickering guaranteed.

# Wait half miliseconds
new_window.after(500, lambda: new_window.resizable(False, False))

Modified version of your code:

import customtkinter
def open_new_window():
    def lock_and_fill_window():
        # Create a CTk button with functionality inside the new window
        new_window.resizable(False, False)
        close_button1 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button2 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button3 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button4 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button5 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button6 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button7 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button8 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button9 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button10 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button1.pack()
        close_button2.pack()
        close_button3.pack()
        close_button4.pack()
        close_button5.pack()
        close_button6.pack()
        close_button7.pack()
        close_button8.pack()
        close_button9.pack()
        close_button10.pack()
        
        
        
    new_window = customtkinter.CTkToplevel(app)
    new_window.grab_set()
    new_window.title("New Window")
    new_window.geometry("1000x800")

    # Wait half miliseconds
    new_window.after(500, lock_and_fill_window)

# Main CTk window
app = customtkinter.CTk()
app.geometry("1000x800")
customtkinter.set_appearance_mode("dark")  # Set dark theme

# Main window button with command to open the new window
main_button = customtkinter.CTkButton(app, text="Open New Window", command=open_new_window)
main_button.pack()

# Start the main event loop
app.mainloop()

Hope, it will be helpful.
Regards.

[ageekhere]

Testing on windows 11

I have also tried this approach, however it does not solve the white flicker issue but only delays it. When def lock_and_fill_window() is called you then get the white flash when the delay is done, very noticeable when using new_window.resizable(False, False), less noticeable without it though still there.

Here is what it looks like using your posted code

white.flash.issue.mp4

[dipeshSam]

@ageekhere

Got it! Here is your solution:

I closely inspected the problem and found that the issue persists because of internal overriding of .resizable() function in CTkToplevel class which delays in setting title bar color of the window, and not in setting background color only. So, let's define external handles for them.

Updated code:

import customtkinter
from customtkinter import CTkToplevel
from customtkinter import get_appearance_mode
from tkinter import Toplevel
import ctypes, sys

def external_handle_for_titlebar(win: CTkToplevel):
    color_mode = get_appearance_mode()

    if sys.platform.startswith("win"):
        if color_mode.lower() == "dark":
            value = 1
        elif color_mode.lower() == "light":
            value = 0
        else:
            return

        try:
            hwnd = ctypes.windll.user32.GetParent(win.winfo_id())
            DWMWA_USE_IMMERSIVE_DARK_MODE = 20
            DWMWA_USE_IMMERSIVE_DARK_MODE_BEFORE_20H1 = 19

            # try with DWMWA_USE_IMMERSIVE_DARK_MODE
            if ctypes.windll.dwmapi.DwmSetWindowAttribute(hwnd, DWMWA_USE_IMMERSIVE_DARK_MODE,
                                                            ctypes.byref(ctypes.c_int(value)),
                                                            ctypes.sizeof(ctypes.c_int(value))) != 0:
                # try with DWMWA_USE_IMMERSIVE_DARK_MODE_BEFORE_20h1
                ctypes.windll.dwmapi.DwmSetWindowAttribute(hwnd, DWMWA_USE_IMMERSIVE_DARK_MODE_BEFORE_20H1,
                                                            ctypes.byref(ctypes.c_int(value)),
                                                            ctypes.sizeof(ctypes.c_int(value)))

        except Exception as err:
            print(err)
            
        finally:
            win.lift()

def external_handle_for_resizable(toplevel: CTkToplevel):
    # Create a CTk button with functionality inside the new window
    Toplevel.resizable(toplevel, False, False)
    external_handle_for_titlebar(toplevel)
    

def open_new_window():
    def fill_window():
        close_button1 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button2 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button3 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button4 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button5 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button6 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button7 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button8 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button9 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button10 = customtkinter.CTkButton(new_window, text="Close", command=new_window.destroy)
        close_button1.pack()
        close_button2.pack()
        close_button3.pack()
        close_button4.pack()
        close_button5.pack()
        close_button6.pack()
        close_button7.pack()
        close_button8.pack()
        close_button9.pack()
        close_button10.pack()
        
    new_window = customtkinter.CTkToplevel(app)
    new_window.grab_set()
    new_window.title("New Window")
    new_window.geometry("1000x800")

    # Resizable operation using external handle.
    external_handle_for_resizable(new_window)
    fill_window()
    
    

# Main CTk window
app = customtkinter.CTk()
app.geometry("1000x800")
customtkinter.set_appearance_mode("dark")  # Set dark theme

# Main window button with command to open the new window
main_button = customtkinter.CTkButton(app, text="Open New Window", command=open_new_window)
main_button.pack()

# Start the main event loop
app.mainloop()

Output:

Let me know whether it is now helpful or not.
Regards.

[dipeshSam]

Thank you @Anonymous6598 😊.

[ageekhere]

That has solved the issue, well done!

[dipeshSam]

You are welcome @ageekhere .

Keep your CustomTkinter journey continue.
Regards.

[ageekhere]

Just a quick update to help others ,it seems that new_window.grab_set() can still create a white flash for me, using new_window.transient(app) instead has totally removed that white flash.

[dipeshSam]

Yeah. More could be said that the position (in program execution sequence) of .grab_set() method may also matter. Calling this method after all the operations are done, might be helpful.