zgui: support high DPI screens (retina)

[tanis2000]

It would be nice if you could add support for high DPI screens like Retina displays in zgui.

What I have seen some people do is to grab the DisplaySize and FramebufferScale vectors from ImGui's ImDrawData and just multiply them together to get the actual viewport size to apply. I believe everything else can be left intact.

[michal-z]

High DPI is already supported. The correct way is to use:
style.scaleAllSizes(scale_factor);
Take a look at the gui_test_wgpu sample application.

Also see: https://github.com/ocornut/imgui/blob/master/docs/FAQ.md#q-how-should-i-handle-dpi-in-my-application

[michal-z]

@tanis2000 Can we close this issue?

[tanis2000]

I have not yet had the chance to check that out. I am working on this project on and off. I will try to have a look at it today and update the ticket.

[tanis2000]

Ok I just tested this both in my game and with the gui_test_wgpu sample and it doesn't really look correct. Or at least this is not what I would expect :)

Here is the sample project running first on the high dpi screen (a Retina MBP monitor) and then on a low dpi 1080p monitor. I just run the project starting on the hdpi screen and then dragged it to the ldpi screen and this is the result:

This doesn't really look like the expected behavior.

I noticed in the logs that the hdpi reports a window size of 3024x1832 and the ldpi a window size of 1512x916
And, in fact, the scale_factor of the hdpi is being set to 2 for the hdpi screen.

I tried to move the code that calculates the scale_factor before the zgui.backend.newFrame so that it gets the right scale not just during the initialization but it has a weird side effect where the title bar of the window seems to take over the whole screen. I haven't checked yet how the 'scaleAllSizes' function works under the hood.

[michal-z]

Opening a window on a HDPI screen and dragging it to LDPI window is not supported currently. I need to think about this case. Thanks for checking it.

[tanis2000]

Fair enough. Please feel free to close this issue if you do not need as a reference for that use-case :)

[michal-z]

Let's leave this open I would like to support this case.