Allow set application-wide default font

[RussKie]

Resolves #3001

Proposed changes

The default font has been updated in .NET Core 3.0 (#656) and documented. However for some users who built their apps in pixel-perfect manner this change has proved to be a significant hurdle in migrating their apps to .NET.

Allow setting application-wide default font in a similar manner we set high dpi or visual styles:

class Program
{
    [STAThread]
    static void Main()
    {
        Application.SetHighDpiMode(HighDpiMode.SystemAware);
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);

+       Application.SetDefaultFont(new Font(new FontFamily("Microsoft Sans Serif"), 8f));

        Application.Run(new Form1());
    }
}

• The application-wide default font can only be set before the first window is created by an application.
• The font will be scaled by the system text scale factor, whenever it is getting changed.

Screenshots

• Microsoft Sans Serif, 8pt
  

• Chiller, 12pt
  

• Calibri, 11pt
  

• System text scale factor changes
  

Test methodology

• several new unit tests
• manual - see below

Microsoft Reviewers: Open in CodeFlow

[kirsan31]

Added handling of the system-wide font scaling events, e.g.:

Wow - nice! 👍 Now we need only #3583 :))))

[dreddy-work]

We may want to cross verify the serialization part for Font with this new change

[RussKie]

Tested different font scaling coupled with different DPI scaling.
There is an observable little deviation in our scaled fonts compared to the scaled system fonts in the range of 101-149%, but it doesn't appear to be visually significant.

100% DPI scale factor

• 100% text scale factor
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=9, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=9, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=172, Height=25}
  MainForm: Minimum form size: {Width=378, Height=448}
• 130%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=11.25, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=11.7, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=227, Height=31}
  MainForm: Minimum form size: {Width=488, Height=526}
• 110%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=9.75, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=9.900001, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=201, Height=29}
  MainForm: Minimum form size: {Width=436, Height=500}
• 225%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=20.25, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=20.25, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=382, Height=47}
  MainForm: Minimum form size: {Width=798, Height=751}
• 175%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=15.75, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=15.75, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=297, Height=40}
  MainForm: Minimum form size: {Width=628, Height=653}
• 150%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=13.5, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=13.5, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=255, Height=35}
  MainForm: Minimum form size: {Width=544, Height=583}

150% DPI scale factor

• 100%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=9, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=9, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=255, Height=35}
  MainForm: Minimum form size: {Width=550, Height=595}
• 130%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=11.5, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=11.7, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=340, Height=42}
  MainForm: Minimum form size: {Width=720, Height=686}
• 225%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=20.5, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=20.25, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=568, Height=65}
  MainForm: Minimum form size: {Width=1176, Height=1011}
• 150%
  MainForm: MessageBoxFont: [Font: Name=Segoe UI, Size=13.5, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Default font: [Font: Name=Segoe UI, Size=13.5, Units=3, GdiCharSet=1, GdiVerticalFont=False]
  MainForm: Biggest button size: {Width=382, Height=47}
  MainForm: Minimum form size: {Width=804, Height=759}

[RussKie]

⚠️ Each form had to be closed and reopened after each dpi/text scale changes

Tested with HighDpiMode.PerMonitorV2:

dpi/text	current default font (SystemFonts.MessageBoxFont)	SetDefaultFont(Calibri, 11)
100% dpi / 100% text
100% dpi / 150% text
150% dpi / 150% text
150% dpi / 100% text

[dreddy-work]

⚠️ Each form had to be closed and reopened after each dpi/text scale changes

Is this because Font is not applied on the windows after UserPreference settings changed? Did you try that? That would trigger layout and scaling of controls.

[dreddy-work]

FYI- this can be dual check-in to preview 5 when ready. Had to close preview 5 so tagging it to Preview 6 for now.