How to write High-DPI aware plugins

[Aivars]

If you're writing plugins and you've seen an issue like this:


this happens because user has enabled Text Zoom in Windows settings. The problem arises from the fact that Windows automatically scales text according to user settings, but not forms and control placement (which you specify in pixels in plugins).

Take a look at this regular plugin code dealing with GUI:

Code: Select all

    f = new TForm(WeBuilder);
    f.Width = 600;
    f.Height = 670;

    var pnlCurrentWBProject = new TPanel(f);
    pnlCurrentWBProject.Parent = f;
    pnlCurrentWBProject.SetBounds(14, 10, 568, 80);

Everything is fine on normal screens, but if someone (like me) would execute this code on Surface Pro, every normal pixel is twice as small on this screen so the text zoom is set to 200%, which means that for this form I will see a tiny form with tiny controls (two times smaller in width and height than on a regular screen) due to my DPI.

Here's how to fix it and make it DPI-aware:

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    f = new TForm(WeBuilder);
    var mul = Round(f.PixelsPerInch / 96);
    f.Width = 600 * mul;
    f.Height = 670 * mul;

    var pnlCurrentWBProject = new TPanel(f);
    pnlCurrentWBProject.Parent = f;
    pnlCurrentWBProject.SetBounds(14 * mul, 10 * mul, 568 * mul, 80 * mul);

The main thing to pay attention to is TForm.PixelsPerInch property. It is 96 on regular screens but bigger (according to Text Zoom setting) on High-DPI screens.

I hope that helps!

[pmk65]

Great. But shouldn't the "96" you divide with, match the "PixelsPerInch" of the system the plugin is created on?

If I do:

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 f = new TForm(WeBuilder);
Script.Message(_t(f.PixelsPerInch));

I get the value "120". So I would assume that's the value I have to use in my plugins?

[Aivars]

It means that you have set Windows Text Zoom to 125%. I don't think it matters much if you use 120 or 96 as baseline, you just get a different multiplier and you accordingly would use different dimensions and coordinates. To convert existing scripts, in your case it might be easier to use 120, but if you're writing a new script, I would recommend using 96 because that's 100% (no zoom).