VST GUI does not work under JUCE-based hosts

[nickdowell]

Hosts that exhibit this problem include:

• JUCE/examples/audio plugin host
• Tracktion

The amsynth GUI displays fine but mouse clicks are not detected.

This is because GTK button press events are not being generated - using gdk_event_handler_set to inspect all events reveals that GDK is not emitting GDK_BUTTON_PRESS events.

An initial round of debugging points to this being an issue with the way JUCE forwards XEvents to the plugin's child window. JUCE uses XSendEvent (see juce_VSTPluginFormat.cpp) but GDK seems to ignore mouse clicks that have the send_event flag set - whether this is intentional or not I do not yet know.

A crude workaround is to not reparent amsynth's GUI window inside the JUCE-owned parent. Event handling then works fine, but this leads to two top-level windows being seen.

Installing an _XEventProc may offer a solution, but so far attempts to get this working on a 64-bit machine have caused crashes. It's not clear whether this mechanism is widely used and therefore reliably implemented in hosts.

Further investigation required...

• _XEventProc 64-bit support
• mouse event handling
• popup menus
• parameter value tooltips

[nickdowell]

Commit 7796664 fixes mouse handling; knobs and buttons now work.
Pop-up menus are currently broken, though.
Investigation continues...