Bug report

Bug description:

>>> import tkinter
>>> from tkinter.font import Font
>>> root = tkinter.Tk()
>>> f1 = Font(name='TkDefaultFont', exists=True)
>>> f1.actual()
{'family': 'Noto Sans', 'size': 20, 'weight': 'normal', 'slant': 'roman', 'underline': 0, 'overstrike': 0}
>>> f2 = f1.copy()
>>> f2.actual()
{'family': 'Noto Sans', 'size': 40, 'weight': 'normal', 'slant': 'roman', 'underline': 0, 'overstrike': 0}
>>> f3 = f2.copy()
>>> f3.actual()
{'family': 'Noto Sans', 'size': 80, 'weight': 'normal', 'slant': 'roman', 'underline': 0, 'overstrike': 0}
>>> f4 = f3.copy()
>>> f4.actual()
{'family': 'Noto Sans', 'size': 160, 'weight': 'normal', 'slant': 'roman', 'underline': 0, 'overstrike': 0}

The example above is from Ubuntu 24.04 running on an Asus Zenbook with EVO screen. The display scaling from the system settings is the default, namely 200%. This does not happen when the display scaling is 100%.

Note that font f1 is already (more than) doubled in size, compared to what wish8.6 (built from 8.6.15 source) reports:

% info patchlevel
8.6.15
% font actual TkDefaultFont
-family {Noto Sans} -size 9 -weight normal -slant roman -underline 0 -overstrike 0
% font config TkDefaultFont
-family sans-serif -size -12 -weight normal -slant roman -underline 0 -overstrike 0

The negative value -12 means that the size is 12 pixels, as opposed to 12 points. I think the intitial expansion being slightly more than a factor of 2 may be caused by rounding when converting pixels to points.

Note that the behavior of Tk 9 is different. Using wish9.0 on the same system produces:

% info patchlevel
9.0.0
% font actual TkDefaultFont
-family {Noto Sans} -size 10 -weight normal -slant roman -underline 0 -overstrike 0
% font config TkDefaultFont
-family sans-serif -size 10 -weight normal -slant roman -underline 0 -overstrike 0

Also, the pending new version of tkinter from #124156 does not have this doubling behavior when used with Tk 9.0. (I have not tested the new tkinter with Tk 8.6, but I expect it to have the broken behavior since I don't think that the PR changes Font.copy.)

CPython versions tested on:

3.12

Operating systems tested on:

Linux