Feature request: Change Windows default OS font

[Jason-GitH]

BACKGROUND: Monitors with non-RGB stripe subpixel layouts suffer from blurry text or color fringing within Windows. There is a long-standing popular feature request for PowerToys to improve subpixel rendering, which seems to be beyond the scope of PowerToys team (#25595 (comment)). However, there is a potential workaround. Utilizing other fonts such as Tahoma (the legacy Windows default font) in combination with disabling ClearType can rectify the font issues at least with WOLED (WBGR stripe subpixel). I think it would be nice to have the ability to change Windows OS font in all areas of OS as it has potential to improve text readability on non-RGB stripe monitors and provide more customizability to Windows. There are multiple Feedback Hub requests regarding the desire to change Windows UI font, not specifically related to OLED.

SOLUTIONS:
Option 1: The default OS font can be forced by modifying registry values. Steps are described here: https://www.howtogeek.com/716407/how-to-change-the-default-system-font-on-windows-10/#how-to-change-the-default-system-font-using-registry-editor.

Here is my Windows Explorer with Tahoma font forced via registry with ClearType disabled displayed on an LG WOLED panel. You can see the text areas in main windows are very sharp but there is still some boldening applied to title bar.

To force Windows OS to use any font you like:
-Step 1: Backup registry.

-Step 2: Install and/or choose a font you like. Identify the font name by going to Settings > Personalization > Fonts. Tahoma is available at default.

-Step 3: Paste the following into Notepad and change "NEW-FONT" to your "FONTNAME" (e.g., Tahoma):

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts]
"Segoe UI (TrueType)"=""
"Segoe UI Bold (TrueType)"=""
"Segoe UI Bold Italic (TrueType)"=""
"Segoe UI Italic (TrueType)"=""
"Segoe UI Light (TrueType)"=""
"Segoe UI Semibold (TrueType)"=""
"Segoe UI Symbol (TrueType)"=""
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontSubstitutes]
"Segoe UI"="NEW-FONT"

-Step 4: Save file as *.reg.
-Step 5: Right click and select Merge. Restart PC.

To revert back to default OS font (Segoe UI):
-Step 1: Create a new Notepad file using the following:

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts]
"Segoe UI (TrueType)"="segoeui.ttf"
"Segoe UI Black (TrueType)"="seguibl.ttf"
"Segoe UI Black Italic (TrueType)"="seguibli.ttf"
"Segoe UI Bold (TrueType)"="segoeuib.ttf"
"Segoe UI Bold Italic (TrueType)"="segoeuiz.ttf"
"Segoe UI Emoji (TrueType)"="seguiemj.ttf"
"Segoe UI Historic (TrueType)"="seguihis.ttf"
"Segoe UI Italic (TrueType)"="segoeuii.ttf""Segoe UI Light (TrueType)"="segoeuil.ttf"
"Segoe UI Light Italic (TrueType)"="seguili.ttf"
"Segoe UI Semibold (TrueType)"="seguisb.ttf"
"Segoe UI Semibold Italic (TrueType)"="seguisbi.ttf"
"Segoe UI Semilight (TrueType)"="segoeuisl.ttf"
"Segoe UI Semilight Italic (TrueType)"="seguisli.ttf"
"Segoe UI Symbol (TrueType)"="seguisym.ttf"
"Segoe MDL2 Assets (TrueType)"="segmdl2.ttf"
"Segoe Print (TrueType)"="segoepr.ttf"
"Segoe Print Bold (TrueType)"="segoeprb.ttf"
"Segoe Script (TrueType)"="segoesc.ttf"
"Segoe Script Bold (TrueType)"="segoescb.ttf"

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontSubstitutes]

"Segoe UI"=-

-Step 2: Save as *.reg & right click Merge. Restart PC.

Option 2: I came across this utility to change Windows fonts on the fly but it just crashes anytime I use it. I wouldn't recommend using it, but PowerToys could implement something similar: https://www.wintools.info/index.php/advanced-system-font-changer#:~:text=The%20Advanced%20System%20Font%20Changer,of%20how%20text%20is%20displayed.

Originally posted by @Jason-GitH in #25595 (comment)

[BoffinBrain]

Have you tried using ClearType in grayscale mode? There's also a tool here to help with that: https://github.com/bp2008/BetterClearTypeTuner

[Jason-GitH]

Have you tried using ClearType in grayscale mode? There's also a tool here to help with that: https://github.com/bp2008/BetterClearTypeTuner

Hello, yes. In fact, you need to use grayscale antialiasing (either by disabling ClearType or using BCCT) to reduce color fringing on WOLED. Unfortunately, this reportedly does not resolve fringing on first generation QD-OLED panels. Additionally, WOLED still suffers from clarity issues with the default Windows OS font (Segoe UI), which led to my interest in changing the default OS font back to the legacy default OS font (Tahoma).