Multiple screens with different resolutions cause render bugs

[RockyF]

It works fine on a MacBook Pro Retina Screen, but shrinks on an external monitor, as shown here:

[joaodasilva]

Thanks for the report; this should be easy to reproduce.

The problem is likely a mismatch between the devicePixelRatio in the retina screen (probably 2x) vs the external monitor (1x). The native window is getting scaled, but the backing rendering canvas isn't.

This is because windowjs looks only at the main monitor and doesn't update its internal state for multiple monitors.

The scaling to use is loaded once here:

windowjs/src/window.cc

Line 107 in d4d9f11

retina_scale_ = (float) width_ / window_width;

GLFW has an API to get the GLFWWindow's monitor:

https://www.glfw.org/docs/latest/window_guide.html#window_monitor

So we could check if the monitor has changed whenever the window moves or gets resized, and fix the scaling factor when that happens.

Even better, GLFW has a callback when the scaling factor has been updated due to moving the window across monitors:

https://www.glfw.org/docs/latest/group__window.html#gaf2832ebb5aa6c252a2d261de002c92d6

I'd be happy to have a look at patches for this :-)