I’ve done more tests.
Interessant result : it works almost (always 2 windows, one in (0,0) with the UI) on Openbox but it doesn’t (the 2 windows glitched) on Fluxbox. It works on LXDE, which is based on Openbox.
It doesn’t do it at all with EXWM, a WM for Emacs, so no compositor, not border, etc. at all. But it does it when I start xfwm4 in.
So It seems to be a problem with the position of the window. Like a bad range. With WM where it doesn’t work, I get one time an assert from X11, about bad range for the position of the window.
I try to follow the flow in the JUCE code. In juce_LV2PluginFormat.cpp, in createView(), configuredEditor->getBounds() returns (0,0).
If useful I’ll redo tests and post these assertions.
It may be a problem with win position because : I have written a personal border for my windows, it uses getDistanceFromDragStart, getScreenPosition, setSize and setTopLeftPosition. It works well only in the WM where there is not the problem, that’s correlated. In the others, the drag gets crazy, there are jumps in getDistanceFromDragStart values, I’ll check this.
But there are some plugins which doesn’t work even on Openbox, EXWM or Mate, for example LV2-Sorcer. Got two windows, both are glitched. Btw an assert in juce_LV2PluginFormat.cpp:2618, jassert (widget != nullptr);
Note that there no problem, in every WM, with Carla, the plugin host of falktx.