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VST GUI does not work under JUCE-based hosts #22

nickdowell opened this issue Aug 16, 2016 · 1 comment


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commented Aug 16, 2016

Hosts that exhibit this problem include:

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 nickdowell added the bug label Aug 16, 2016

@nickdowell nickdowell added this to the 1.7.0 milestone Aug 16, 2016

@nickdowell nickdowell self-assigned this Aug 16, 2016


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commented Aug 27, 2016

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

nickdowell added a commit that referenced this issue Aug 27, 2016

nickdowell added a commit that referenced this issue Aug 28, 2016

nickdowell added a commit that referenced this issue Aug 28, 2016

fix popup menus under JUCE VST
gtk_menu_popup() was failing when called from button-press-event
handler, but works from button-release-event


@nickdowell nickdowell closed this Oct 1, 2016

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