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>

1 files changed, 44 insertions, 2 deletions

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);