Fix double tap & drag on Android

[OmarShehata]

This fixes #76587. This is very easy to reproduce, just compile on Android device a project which prints all input events:

extends Node2D
func _input(event):
	print(event)

In master, if you double tap & drag, no events are emitted for the drag. In this PR, you correctly see the drag events. This makes Android consistent with iOS and Windows (I haven't tested other platforms behavior).

The fix involves listening for motion events in the onDoubleTapEvent listener, because the native Android GestureDetector differentiates between motion events after a double tap and regular motion events.

[OmarShehata]

I am not sure why this was always returning true even for cases when it wasn't actually handling the event. I've changed it to only return true when it handles the event, consistent with the other event listeners here.

[m4gr3d]

This doesn't look correct, this callback should receive both down and up events and with this update the logic now returns false for down events, which would have the effect of cancelling the next up event.
Can you log the events passing through this method and check we are still receiving the expected flow.

[OmarShehata]

Also, is this correct, that a ACTION_UP should trigger a motion event?

[m4gr3d]

That's correct, this correspond to the release of the double tap event.

[m4gr3d]

This doesn't look correct, this callback should receive both down and up events and with this update the logic now returns false for down events, which would have the effect of cancelling the next up event.
Can you log the events passing through this method and check we are still receiving the expected flow.

[OmarShehata]

Thanks for the feedback @m4gr3d, I've force pushed an update (my understanding this is the preferred workflow to keep the commit history squashed). It now maintains the original behavior, but just handles the motion event.

I was able to confirm with additional logging the incorrect behavior you expected in my original attempt. We get an ACTION_DOWN event triggered here that we need to return true for but that should NOT trigger a handleMotionEvent (otherwise it triggers more events than expected).

[OmarShehata]

Also just noting down here, this could be implemented in the following way and I tested that it has the same behavior (my test was double tap, drag, & release, and comparing the events emitted on the GDScript side):

override fun onDoubleTapEvent(event: MotionEvent): Boolean {
	if (event.actionMasked == MotionEvent.ACTION_UP) {
		nextDownIsDoubleTap = false
		GodotInputHandler.handleMotionEvent(event)
		return true
	}
	if (event.actionMasked == MotionEvent.ACTION_MOVE) {
		GodotInputHandler.handleMotionEvent(event)
		return true
	}
	if (event.actionMasked == MotionEvent.ACTION_DOWN) {
		// No need to handle this, just need to return true
		// otherwise you get 2 extra events (pressed=true & pressed=false) when double tapping
		return true
	}
	return false
}

The version I pushed is more concise/closer to the original code.

[m4gr3d]

Thanks for the update, this looks like it should handle the issue!

There's one more scenario to consider and incorporate in the logic; when panning and scaling is enabled (panningAndScalingEnabled == true), the ScaleGestureDetector logic treats double_tap followed by swipe as a magnify event:

• For the documentation, see https://developer.android.com/reference/android/view/ScaleGestureDetector#setQuickScaleEnabled(boolean)
• And the scale callback is

  godot/platform/android/java/lib/src/org/godotengine/godot/input/GodotGestureHandler.kt

  Line 242 in cf8ad12

  override fun onScale(detector: ScaleGestureDetector): Boolean {

  .

This capability is still private (not exposed to GDScript) and only being used by the Android editor to support scaling in the spatial editor.
To complement your fix and not break that functionality, you'll need to check that panningAndScalingEnabled == false before forwarding the motion event.

[OmarShehata]

@m4gr3d just updated to prevent handling the event in the case of panningAndScalingEnabled == false. I've never used the Android version of the editor before, but I tested this by enabling panning & scaling as follows, and checking that when it is enabled, we go back to the old behavior (no drag events emitted after double tap)

this.godotGestureHandler.setPanningAndScalingEnabled(true);

Let me know if this looks right!

[m4gr3d]

Looks great, thanks for the fix!

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[OmarShehata]

Thank you so much @akien-mga !! Thank you & all the contributors who spent the time & effort creating this amazing engine & documenting everything so well that made me feel confident enough to give this a shot 🙏

[akien-mga]

Cherry-picked for 4.0.3.

[akien-mga]

Cherry-picked for 3.6.

[akien-mga]

This fix can't be cherry-picked for 3.5.x as is, the code is significantly different and I can't find easily where to do a similar change.