[Bug]: tkinter backend changes DPI awareness context of entire process on Windows · Issue #21875 · matplotlib/matplotlib · GitHub

Bug summary

_BackendTk.new_figure_manager_given_figure calls _c_internal_utils.Win32_SetProcessDpiAwareness_max, which affects the entire process attached to the script, and all windows part of it, rather than just the matplotlib output window.

Ideally, the DPI awareness context should only be changed for the current thread before a matplotlib window is drawn and returned to the previous value afterwards, or at the very least there should be an option to disable the DPI change.

Code for reproduction

# reproduces the bug when run on a high DPI display on Windows

import tkinter as tk
from tkinter import ttk

import matplotlib
matplotlib.use('TkAgg')  # in case other GUI libraries are installed
import matplotlib.pyplot as plt

root = tk.Tk()

button = ttk.Button(root, text="Run matplotlib.pyplot.subplots",
                    command=plt.subplots)
button.pack(padx=30, pady=30)

root.wait_window()  #root.mainloop seems to prevent DPI updates

Actual outcome

The scaling of the window changes.

Expected outcome

The scaling of the window shouldn't change just because subplots was called.

Additional information

Introduced in #19167

Operating system

Windows 10

Matplotlib Version

3.5.0

Matplotlib Backend

TkAgg

Python version

3.9.6

Jupyter version

No response

Installation

pip

As a workaround you can call ctypes.windll.shcore.SetProcessDpiAwareness(0) before engaging the TkAgg backend. It might be good to have a setting that causes TkAgg to skip setting DPI awareness since the semantics of it are weird.

A potential way of avoiding this issue in Windows 10 version 1803 onwards would be to use SetThreadDpiHostingBehavior and SetThreadDpiAwarenessContext to only apply the scaling to a matplotlib popup window. Having a setting to disable it would always be good though when using an API call that applies to the entire process.

xref: https://discourse.matplotlib.org/t/figures-are-wrong-size-after-using-tk-filedialog-askopenfilename/22458

mpl dpi bug workaround

[Bug]: tkinter backend changes DPI awareness context of entire process on Windows · Issue #21875 · matplotlib/matplotlib · GitHub

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[Bug]: tkinter backend changes DPI awareness context of entire process on Windows #21875

Bug summary

Code for reproduction

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Expected outcome

Additional information

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Matplotlib Backend

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[Bug]: tkinter backend changes DPI awareness context of entire process on Windows · Issue #21875 · matplotlib/matplotlib · GitHub

Repository navigation

[Bug]: tkinter backend changes DPI awareness context of entire process on Windows #21875

Description

Bug summary

Code for reproduction

Actual outcome

Expected outcome

Additional information

Operating system

Matplotlib Version

Matplotlib Backend

Python version

Jupyter version

Installation

Activity

richardsheridan commented on Dec 6, 2021

daniilS commented on Dec 6, 2021

tacaswell commented on Dec 15, 2021

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