Use runtime detection of XInput 2.1 to disable legacy wheel events

Ensure we fall back to using wheel button events if xinput 2.1
scroll events are not available. Handles lack of xinput 2.1
support in the server or in the input devices drivers.

Task-number: QTBUG-38169
Change-Id: Ie4ad9069f648d0ab02d8f9540ed01ad58fd9e9d8
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

4 files changed, 76 insertions, 13 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index f5f6c712c5..e3b81c2b40 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -1791,6 +1791,19 @@ bool QXcbConnection::xi2GetValuatorValueIfSet(void *event, int valuatorNum, doub
     return true;
 }
 
+bool QXcbConnection::xi2GetButtonState(void *event, int buttonNum)
+{
+    xXIDeviceEvent *xideviceevent = static_cast<xXIDeviceEvent *>(event);
+    unsigned char *buttonsMaskAddr = (unsigned char*)&xideviceevent[1];
+
+    for (int i = 0; i < (xideviceevent->buttons_len * 4); i++) {
+        if (buttonNum < 8)
+            return (buttonsMaskAddr[i] & (1 << buttonNum));
+        buttonNum -= 8;
+    }
+    return false;
+}
+
 // Starting from the xcb version 1.9.3 struct xcb_ge_event_t has changed:
 // - "pad0" became "extension"
 // - "pad1" and "pad" became "pad0"
diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 13a0280baf..1933b89a19 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -402,6 +402,12 @@ public:
 #elif defined(XCB_USE_XINPUT2)
     void xi2Select(xcb_window_t window);
 #endif
+#ifdef XCB_USE_XINPUT21
+    bool isUsingXInput21() { return m_xi2Enabled && m_xi2Minor >= 1; }
+#else
+    bool isUsingXInput21() { return false; }
+#endif
+
 
     void sync();
     void flush() { xcb_flush(m_connection); }
@@ -511,11 +517,12 @@ private:
     QVector<TabletData> m_tabletData;
 #endif
     struct ScrollingDevice {
-        ScrollingDevice() : deviceId(0), verticalIndex(0), horizontalIndex(0), orientations(0) { }
+        ScrollingDevice() : deviceId(0), verticalIndex(0), horizontalIndex(0), orientations(0), legacyOrientations(0) { }
         int deviceId;
         int verticalIndex, horizontalIndex;
         double verticalIncrement, horizontalIncrement;
         Qt::Orientations orientations;
+        Qt::Orientations legacyOrientations;
         QPointF lastScrollPosition;
     };
     void xi2HandleScrollEvent(void *event, ScrollingDevice &scrollingDevice);
@@ -525,6 +532,7 @@ private:
 #if defined(XCB_USE_XINPUT2) || defined(XCB_USE_XINPUT2_MAEMO)
     static bool xi2GetValuatorValueIfSet(void *event, int valuatorNum, double *value);
     static bool xi2PrepareXIGenericDeviceEvent(xcb_ge_event_t *event, int opCode);
+    static bool xi2GetButtonState(void *event, int buttonNum);
 #endif
 
     xcb_connection_t *m_connection;
diff --git a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
index d7b3c75aee..831ccba6f6 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
@@ -134,7 +134,6 @@ void QXcbConnection::initializeXInput2()
 #ifdef XCB_USE_XINPUT21
                     case XIScrollClass: {
                         XIScrollClassInfo *sci = reinterpret_cast<XIScrollClassInfo *>(devices[i].classes[c]);
-                        scrollingDevice.deviceId = devices[i].deviceid;
                         if (sci->scroll_type == XIScrollTypeVertical) {
                             scrollingDevice.orientations |= Qt::Vertical;
                             scrollingDevice.verticalIndex = sci->number;
@@ -147,6 +146,20 @@ void QXcbConnection::initializeXInput2()
                         }
                         break;
                     }
+                    case XIButtonClass: {
+                        XIButtonClassInfo *bci = reinterpret_cast<XIButtonClassInfo *>(devices[i].classes[c]);
+                        for (int i=0; i < bci->num_buttons; ++i) {
+                            const int buttonAtom = qatom(bci->labels[i]);
+                            if (buttonAtom == QXcbAtom::ButtonWheelUp
+                                || buttonAtom == QXcbAtom::ButtonWheelDown) {
+                                scrollingDevice.legacyOrientations |= Qt::Vertical;
+                            } else if (buttonAtom == QXcbAtom::ButtonHorizWheelLeft
+                                       || buttonAtom == QXcbAtom::ButtonHorizWheelRight) {
+                                scrollingDevice.legacyOrientations |= Qt::Horizontal;
+                            }
+                        }
+                        break;
+                    }
 #endif
                     default:
                         break;
@@ -170,7 +183,10 @@ void QXcbConnection::initializeXInput2()
 #endif // QT_NO_TABLETEVENT
 
 #ifdef XCB_USE_XINPUT21
-                if (scrollingDevice.orientations) {
+                if (scrollingDevice.orientations || scrollingDevice.legacyOrientations) {
+                    scrollingDevice.deviceId = devices[i].deviceid;
+                    // Only use legacy wheel button events when we don't have real scroll valuators.
+                    scrollingDevice.legacyOrientations &= ~scrollingDevice.orientations;
                     m_scrollingDevices.insert(scrollingDevice.deviceId, scrollingDevice);
                     if (Q_UNLIKELY(debug_xinput_devices))
                         qDebug() << "   it's a scrolling device";
@@ -256,6 +272,7 @@ void QXcbConnection::xi2Select(xcb_window_t window)
     if (!m_scrollingDevices.isEmpty()) {
         QVector<XIEventMask> xiEventMask(m_scrollingDevices.size());
         bitMask = XI_MotionMask;
+        bitMask |= XI_ButtonReleaseMask;
         int i=0;
         Q_FOREACH (const ScrollingDevice& scrollingDevice, m_scrollingDevices) {
             xiEventMask[i].deviceid = scrollingDevice.deviceId;
@@ -595,6 +612,31 @@ void QXcbConnection::xi2HandleScrollEvent(void *event, ScrollingDevice &scrollin
                 QWindowSystemInterface::handleWheelEvent(platformWindow->window(), xiEvent->time, local, global, rawDelta, angleDelta, modifiers);
             }
         }
+    } else if (xiEvent->evtype == XI_ButtonRelease) {
+        xXIDeviceEvent* xiDeviceEvent = reinterpret_cast<xXIDeviceEvent *>(event);
+        if (QXcbWindow *platformWindow = platformWindowFromId(xiDeviceEvent->event)) {
+            QPoint angleDelta;
+            if (scrollingDevice.legacyOrientations & Qt::Vertical) {
+                if (xi2GetButtonState(xiDeviceEvent, 4))
+                    angleDelta.setY(120);
+                else if (xi2GetButtonState(xiDeviceEvent, 5))
+                    angleDelta.setY(-120);
+            }
+            if (scrollingDevice.legacyOrientations & Qt::Horizontal) {
+                if (xi2GetButtonState(xiDeviceEvent, 6))
+                    angleDelta.setX(120);
+                if (xi2GetButtonState(xiDeviceEvent, 7))
+                    angleDelta.setX(-120);
+            }
+            if (!angleDelta.isNull()) {
+                QPoint local(fixed1616ToReal(xiDeviceEvent->event_x), fixed1616ToReal(xiDeviceEvent->event_y));
+                QPoint global(fixed1616ToReal(xiDeviceEvent->root_x), fixed1616ToReal(xiDeviceEvent->root_y));
+                Qt::KeyboardModifiers modifiers = keyboard()->translateModifiers(xiDeviceEvent->mods.effective_mods);
+                if (modifiers & Qt::AltModifier)
+                    std::swap(angleDelta.rx(), angleDelta.ry());
+                QWindowSystemInterface::handleWheelEvent(platformWindow->window(), xiEvent->time, local, global, QPoint(), angleDelta, modifiers);
+            }
+        }
     }
 #else
     Q_UNUSED(event);
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index ad7e99bd49..386bf16c16 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -1705,16 +1705,16 @@ void QXcbWindow::handleButtonPressEvent(const xcb_button_press_event_t *event)
     Qt::KeyboardModifiers modifiers = connection()->keyboard()->translateModifiers(event->state);
 
     if (isWheel) {
-#ifndef XCB_USE_XINPUT21
-        // Logic borrowed from qapplication_x11.cpp
-        int delta = 120 * ((event->detail == 4 || event->detail == 6) ? 1 : -1);
-        bool hor = (((event->detail == 4 || event->detail == 5)
-                     && (modifiers & Qt::AltModifier))
-                    || (event->detail == 6 || event->detail == 7));
-
-        QWindowSystemInterface::handleWheelEvent(window(), event->time,
-                                                 local, global, delta, hor ? Qt::Horizontal : Qt::Vertical, modifiers);
-#endif
+        if (!connection()->isUsingXInput21()) {
+            // Logic borrowed from qapplication_x11.cpp
+            int delta = 120 * ((event->detail == 4 || event->detail == 6) ? 1 : -1);
+            bool hor = (((event->detail == 4 || event->detail == 5)
+                         && (modifiers & Qt::AltModifier))
+                        || (event->detail == 6 || event->detail == 7));
+
+            QWindowSystemInterface::handleWheelEvent(window(), event->time,
+                                                     local, global, delta, hor ? Qt::Horizontal : Qt::Vertical, modifiers);
+        }
         return;
     }