[vtk-developers] HiDPI / Retina displays and vtkTextActors

[Sean McBride]

On Sat, 14 Oct 2017 11:39:29 +0200, Elvis Stansvik said:

>> Thanks for the quick reply and suggestion.  We just tried this, and
>indeed it works.  Specifically, we did SetDPI(144), we didn't actually
>try to do any introspection of the actual DPI of the actual monitor.
>
>I'm using GetRenderWindow()->SetDPI(q
>Round(QGuiApplication::primaryScreen()->logicalDotsPerInch()))
>in our Qt/VTK app. i.e. using Qt to query for the DPI of the actual
>monitor.

I'm not at all convinced it's better to use the actual screen DPI to achieve this.  The API to get that info on macOS is IODisplayCreateInfoDictionary(), and has just a couple of hundred google results.  It does not seem at all typical to use DPI information.  From what I can tell, the way everyone handles Retina displays is a 2x doubling.

Consider how using the actual DPI would affect the screenshot in the start of this thread... the relative sizes of the cone & text would be different on different screens.  Seems just as undesirable as the current situation.

>Of course, this in itself doesn't take care of DPI changes, and it's
>been on my TODO to fix this (listen for screen changes).

You might also want to not hardcode 'primaryScreen' in there... :)

>It looks like your MR is making VTK do this automatically internally
>on macOS?

Yes, basically.

>That would be a welcome addition indeed, but what about
>other platforms?

Probably desirable there too, but outside my expertise...

Sean