Qt Multi-touch Dials example not working as expected

[dpatel]

Hi,

I am trying to test the Dials Multitouch example which comes along with Qt. I am not sure is the issue in my setup, touch screen or Qt. I am facing exactly same issue (well partially) described here

Here is my project setup.

Qt 4.6.2
Qt Creator 1.3.1
Win 7 32 bit OS
Hp Compaq L2105tm Multitouch Monitor (supports 2 touches)

I am able to compile and run the application with following issues.

Firstly I have to add in main.cpp of the example (to receive multitouch event even for the first time)

QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);

QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);

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In release mode I can rotate two knobs only for the first time for each knob.
Usecases
Rotate knb1 knb2 -> works fine first time
Rotate knb1 knb2 again -> only one knob will rotate.
Rotate knb3 knb4 -> works fine since these knobs are rotated for the first time.
Now any combination of knobs between 1-4 will not work as expected. Only one knob is rotated even if I try to rotate two knobs.

In debug mode all the above cases work fine, i.e I can rotate any combination of two knobs any number of times (70% of times). Sometimes debug build is also not working as expected.

After digging into the issue for two days I found

(1) that in case of failures the touch event is directly received by the knobs and in case of correct behavior the touch event is first received by containing widget of knobs(int this case its QWidget) and from there the event is propagated to respective knob.

(2) In case of correct behavior the code returns from

if (!isActive())
    {
        return;
    }

if (!isActive())
    {
        return;
    }

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which is at around line 230 in qt\src\gui\accessible\qaccessible_win.cpp. While in case of incorrect behavior the code goes further down in that function.

In case if its of any help, here goes the stack trace in case of correct behavior

0	QDial::mouseMoveEvent	qdial.cpp	349	0x00a29e70	
1	QWidget::event	qwidget.cpp	7983	0x006dc938	
2	QAbstractSlider::event	qabstractslider.cpp	956	0x009fbe56	
3	QDial::event	qdial.cpp	508	0x00a2a2a0	
4	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x00692520	
5	QApplication::notify	qapplication.cpp	3865	0x00690723	
6	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
7	QCoreApplication::sendEvent	qcoreapplication.h	215	0x00ce6f9e	
8	QWidget::event	qwidget.cpp	8431	0x006ddbcf	
9	QAbstractSlider::event	qabstractslider.cpp	956	0x009fbe56	
10	QDial::event	qdial.cpp	508	0x00a2a2a0	
11	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x00692520	
12	QApplication::notify	qapplication.cpp	4265	0x006923a0	
13	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
14	QCoreApplication::sendSpontaneousEvent	qcoreapplication.h	218	0x00ce6f4a	
15	QApplicationPrivate::translateRawTouchEvent	qapplication.cpp	5670	0x006941fc	
16	QApplicationPrivate::translateTouchEvent	qapplication_win.cpp	4067	0x006fa075	
17	QtWndProc@16	qapplication_win.cpp	1680	0x006f2e8f	
18	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f86ef	
19	??		0	0x00060534	
20	??		0	0x00000240

0	QDial::mouseMoveEvent	qdial.cpp	349	0x00a29e70	
1	QWidget::event	qwidget.cpp	7983	0x006dc938	
2	QAbstractSlider::event	qabstractslider.cpp	956	0x009fbe56	
3	QDial::event	qdial.cpp	508	0x00a2a2a0	
4	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x00692520	
5	QApplication::notify	qapplication.cpp	3865	0x00690723	
6	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
7	QCoreApplication::sendEvent	qcoreapplication.h	215	0x00ce6f9e	
8	QWidget::event	qwidget.cpp	8431	0x006ddbcf	
9	QAbstractSlider::event	qabstractslider.cpp	956	0x009fbe56	
10	QDial::event	qdial.cpp	508	0x00a2a2a0	
11	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x00692520	
12	QApplication::notify	qapplication.cpp	4265	0x006923a0	
13	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
14	QCoreApplication::sendSpontaneousEvent	qcoreapplication.h	218	0x00ce6f4a	
15	QApplicationPrivate::translateRawTouchEvent	qapplication.cpp	5670	0x006941fc	
16	QApplicationPrivate::translateTouchEvent	qapplication_win.cpp	4067	0x006fa075	
17	QtWndProc@16	qapplication_win.cpp	1680	0x006f2e8f	
18	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f86ef	
19	??		0	0x00060534	
20	??		0	0x00000240

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Stack trace in case of incorrect behavior

0	QWidgetPrivate::registerTouchWindow	qwidget_win.cpp	2050	0x0096e706	
1	QWidgetPrivate::create_sys	qwidget_win.cpp	494	0x00968781	
2	QWidget::create	qwidget.cpp	1319	0x0092ba61	
3	QWidgetPrivate::createWinId	qwidget.cpp	2310	0x0092f84e	
4	QWidget::setAttribute	qwidget.cpp	10392	0x00940f38	
5	QWidget::winId	qwidget.cpp	2281	0x0092f63a	
6	QAccessible::updateAccessibility	qaccessible_win.cpp	286	0x00db2145	
7	QAbstractSlider::setValue	qabstractslider.cpp	539	0x00c5b49a	
8	QAbstractSlider::triggerAction	qabstractslider.cpp	631	0x00c5b6fd	
9	QAbstractSlider::setSliderPosition	qabstractslider.cpp	499	0x00c5b397	
10	QDial::mouseMoveEvent	qdial.cpp	356	0x00c89ef6	
11	QWidget::event	qwidget.cpp	7983	0x0093c938	
12	QAbstractSlider::event	qabstractslider.cpp	956	0x00c5be3a	
13	QDial::event	qdial.cpp	508	0x00c8a284	
14	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x008f2520	
15	QApplication::notify	qapplication.cpp	3865	0x008f0723	
16	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
17	QCoreApplication::sendEvent	qcoreapplication.h	215	0x00f46f7e	
18	QWidget::event	qwidget.cpp	8430	0x0093dbb3	
19	QAbstractSlider::event	qabstractslider.cpp	956	0x00c5be3a	
20	QDial::event	qdial.cpp	508	0x00c8a284	
21	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x008f2520	
22	QApplication::notify	qapplication.cpp	4265	0x008f23a0	
23	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
24	QCoreApplication::sendSpontaneousEvent	qcoreapplication.h	218	0x00f46f2a	
25	QApplicationPrivate::translateRawTouchEvent	qapplication.cpp	5670	0x008f41fc	
26	QApplicationPrivate::translateTouchEvent	qapplication_win.cpp	4067	0x0095a059	
27	QtWndProc@16	qapplication_win.cpp	1680	0x00952e73	
28	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f86ef	
29	??		0	0x00020362	
30	??		0	0x00000240	
31	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f8876	
32	qt_is_translatable_mouse_event	qapplication_win.cpp	1395	0x009520dd	
33	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f89b5	
34	??		0	0x00000000

0	QWidgetPrivate::registerTouchWindow	qwidget_win.cpp	2050	0x0096e706	
1	QWidgetPrivate::create_sys	qwidget_win.cpp	494	0x00968781	
2	QWidget::create	qwidget.cpp	1319	0x0092ba61	
3	QWidgetPrivate::createWinId	qwidget.cpp	2310	0x0092f84e	
4	QWidget::setAttribute	qwidget.cpp	10392	0x00940f38	
5	QWidget::winId	qwidget.cpp	2281	0x0092f63a	
6	QAccessible::updateAccessibility	qaccessible_win.cpp	286	0x00db2145	
7	QAbstractSlider::setValue	qabstractslider.cpp	539	0x00c5b49a	
8	QAbstractSlider::triggerAction	qabstractslider.cpp	631	0x00c5b6fd	
9	QAbstractSlider::setSliderPosition	qabstractslider.cpp	499	0x00c5b397	
10	QDial::mouseMoveEvent	qdial.cpp	356	0x00c89ef6	
11	QWidget::event	qwidget.cpp	7983	0x0093c938	
12	QAbstractSlider::event	qabstractslider.cpp	956	0x00c5be3a	
13	QDial::event	qdial.cpp	508	0x00c8a284	
14	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x008f2520	
15	QApplication::notify	qapplication.cpp	3865	0x008f0723	
16	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
17	QCoreApplication::sendEvent	qcoreapplication.h	215	0x00f46f7e	
18	QWidget::event	qwidget.cpp	8430	0x0093dbb3	
19	QAbstractSlider::event	qabstractslider.cpp	956	0x00c5be3a	
20	QDial::event	qdial.cpp	508	0x00c8a284	
21	QApplicationPrivate::notify_helper	qapplication.cpp	4300	0x008f2520	
22	QApplication::notify	qapplication.cpp	4265	0x008f23a0	
23	QCoreApplication::notifyInternal	qcoreapplication.cpp	704	0x6a1fd302	
24	QCoreApplication::sendSpontaneousEvent	qcoreapplication.h	218	0x00f46f2a	
25	QApplicationPrivate::translateRawTouchEvent	qapplication.cpp	5670	0x008f41fc	
26	QApplicationPrivate::translateTouchEvent	qapplication_win.cpp	4067	0x0095a059	
27	QtWndProc@16	qapplication_win.cpp	1680	0x00952e73	
28	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f86ef	
29	??		0	0x00020362	
30	??		0	0x00000240	
31	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f8876	
32	qt_is_translatable_mouse_event	qapplication_win.cpp	1395	0x009520dd	
33	USER32!IsWindowVisible	C:\Windows\system32\user32.dll	0	0x777f89b5	
34	??		0	0x00000000

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Note:
The FingerPaint example that Qt provides works fine. I can draw with two finger everytimes (since my monitor only supports two simultaneous touches).

Now please enlighten me what going wrong here. I suspect that this issue is related to focus of the widgets.

Any pointers to further investigation or solution are appreciated.

Thanks

[dpatel]

Update:

I have posted the response on another thread but in case someone finds the information useful.

I think I have found the cause of this issue but not sure if that's by design or a bug in QWidget.
As explained in above posts first time two widgets receive multi-touch events but after that only one widget receives touch events.
Usually Qt doesn't create separate native widgets for each widget that is placed upon main window (unless Qt::WA_NativeWindow attribute is set). It only creates one native widget and maintains child widgets. You can confirm this using Spy++ (which comes along with Visual Studio) or similar tool. I found that after the first touch/mouse event, Qt creates a native widget for the knob even if QCoreApplication::setAttribute(Qt::AA_DontCreateNa tiveWidgetSiblings) is done. So now if you touch that knobs it will grab the touch event and won't allow other knobs to receive simultaneous event.

I also made changes in QWidget::winID() and added following code
Qt Code:

if(QCoreApplication::testAttribute(Qt::AA_DontCreateNativeWidgetSiblings)==false)
      that->setAttribute(Qt::WA_NativeWindow);

if(QCoreApplication::testAttribute(Qt::AA_DontCreateNativeWidgetSiblings)==false)
      that->setAttribute(Qt::WA_NativeWindow);

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instead of

that->setAttribute(Qt::WA_NativeWindow);

that->setAttribute(Qt::WA_NativeWindow);

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My changes fixes issue, and now I can move multiple knobs simultaneously more than once. Let me know if someone thinks that this might break something. Also let me know where can I post this issue so that Qt team can fix it or justify current behavior

---

Added after 57 minutes:

FYI:

This is a bug and is already reported to Qt team. You can track it at Qt-BugReport