Ghost touches on windows phone 8

[deluksic]

I'm making a (very awesome) drawing app for windows phone, but I noticed that if I touch the screen with 3+ fingers, the TouchPanel.GetState() returns more and more touches. As if some ghost touches start to appear. There can be as many as 20+ ghost touches at a time.

[Nezz]

Of the debugger is attached, WP8 touchpanel starts acting strange without any apparent reason. Do you experience this without the debugger too?

[deluksic]

Yes, finally someone :) the app is already submitted but I need fix asap. Although, My app doesnt expect the user to tap with three fingers, the bug is annoying and is solvable only by home button to start and then back to app.

[deluksic]

I know you guys are busy making the content pipeline, but can anyone look into this, please? This is a major issue!

[tomspilman]

I know you guys are busy making the content pipeline

That isn't how things work. The team is all volunteers... usually working on parts of MonoGame for fun or because they have a need. Most of the latest WP8 fixes for instance came from @Nezz because he was porting for WP8.

The best thing you can do is make reproducing this issue easy. Setup a test project that reproduces the bug and link to it here. This way someone can download the project and immediately investigate the issue.

[deluksic]

Oh, ok. Thanks for clearing that up. So Im making a test project then..

[deluksic]

sorry for closing/reopening, I was on mobile and pressed the wrong button.

Al right, so I made a test app for you to debug. The bug can be reproduced by tapping on the screen with two or more fingers. After few taps, you should see "fake" taps start appearing. It seems as if the touch collection cache is not clearing up. I also see that the TouchPanel.Clear() is not implemented.

Here is download link to my dropbox: https://www.dropbox.com/s/8wiiyy32oji8779/TouchPanelTest.zip
You can also download my app and try to do the same. When the false touches start appearing, the app becomes unresponsive: http://www.windowsphone.com/s?appid=56c51106-721c-4ad3-b6fd-17fb9a11edfd

EDIT: I did few touch tests and I got to a conclusion that the ghost thouches appear only if you try to touch the screen with two or more fingers in a same frame. You can touch the screen with 10 fingers at once if you touch one by one and nothing happens.

[deluksic]

Update: ghost touches are actually touches that have been made before and are stuck on moving state.

[deluksic]

Could be that the OnPointerReleased event of XamlGame never gets called so the touch stays where it is? Thats the only explanation for now..

[Nezz]

That would be the only way to explain it. But I have to say that we never received reports of such an issue in our WP8 game.

[tomspilman]

I don't remember the details of the WP8 touch events... but are you maybe capturing some pointer events yourself? Maybe via some XAML controls? Are those blocking MonoGame code from receiving some events? This has happened to others before on Win8.

[deluksic]

Hmm.. Well it is a bit harder to reproduce, but possible nontheless. Maybe your app doesnt need multitouch so they never had problems with it?

[Nezz]

It uses pinch to zoom.

[deluksic]

Mine too.. Well, are you able to reproduce the problem, or is it just me?

[deluksic]

@tomspilman thee are no controls except the drawingsurfacegrid.