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System font scaling not working on the fly #14748

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3583 System font scaling not working on the fly
JayashreeSF3546 Jun 30, 2026
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JayashreeSF3546 Jul 10, 2026
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19 changes: 19 additions & 0 deletions src/System.Windows.Forms/System/Windows/Forms/Control.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -12626,6 +12626,7 @@ protected virtual void WndProc(ref Message m)
// s_defaultFont = Application.DefaultFont ?? SystemFonts.MessageBoxFont;
// So we need to check both variants - manually set font (Application.DefaultFont is not null) and auto system font

bool defaultFontChanged = false;
if (Application.DefaultFont is null) // auto system font
{
if (s_defaultFont is not null) // we need to check only if s_defaultFont already set
Expand All @@ -12634,6 +12635,7 @@ protected virtual void WndProc(ref Message m)
if (!s_defaultFont.Equals(font)) // the font has changed
{
s_defaultFont = font;
defaultFontChanged = true;
}
else
{
Expand All @@ -12643,8 +12645,25 @@ protected virtual void WndProc(ref Message m)
}
else // manually set font
{
Font? previousDefaultFont = s_defaultFont;
Application.ScaleDefaultFont(); // will update Application.s_defaultFont or Application.s_defaultFontScaled only if needed
s_defaultFont = Application.DefaultFont; // Application.s_defaultFontScaled ?? Application.s_defaultFont
defaultFontChanged = !s_defaultFont.Equals(previousDefaultFont);
}

// When the system default font changes and controls are using it, notify them so that
// AutoScaleMode.Font can immediately re-scale controls and update their sizes without
// requiring an application restart.
if (defaultFontChanged)
{
s_defaultFontHandleWrapper?.Dispose();
s_defaultFontHandleWrapper = null;
}

if (defaultFontChanged && !TryGetExplicitlySetFont(out _))
{
DisposeFontHandle();
OnFontChanged(EventArgs.Empty);
}
}
}
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