xcb: don't do mouse synthesis from touch unless we find a reason

One reason is when we are using XInput 2.2, because touch devices
will then generate touch events only.  For the other X11 scenarios,
X11 does its own mouse emulation.

QPlatformIntegration::styleHint() wasn't overridden yet.  The remaining
hints are TODO for now.

Change-Id: I2e444a00a18b33ed840ebfa8d8218655c2c39aad
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -257,6 +257,7 @@ QXcbConnection::QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGra
     , has_shape_extension(false)
     , has_randr_extension(false)
     , has_input_shape(false)
+    , has_touch_without_mouse_emulation(false)
     , m_buttons(0)
     , m_focusWindow(0)
 {

src/plugins/platforms/xcb/qxcbconnection.h

@@ -401,6 +401,7 @@ public:
     bool hasXShape() const { return has_shape_extension; }
     bool hasXRandr() const { return has_randr_extension; }
     bool hasInputShape() const { return has_input_shape; }
+    bool hasTouchWithoutMouseEmulation() const { return has_touch_without_mouse_emulation; }
 
     bool supportsThreadedRendering() const { return m_reader->isRunning(); }
 
@@ -543,6 +544,7 @@ private:
     bool has_shape_extension;
     bool has_randr_extension;
     bool has_input_shape;
+    bool has_touch_without_mouse_emulation;
 
     Qt::MouseButtons m_buttons;
 

src/plugins/platforms/xcb/qxcbconnection_xi2.cpp

@@ -92,6 +92,9 @@ void QXcbConnection::initializeXInput2()
             // Tablet support: Find the stylus-related devices.
             xi2SetupTabletDevices();
 #endif // QT_NO_TABLETEVENT
+#ifdef XI2_TOUCH_DEBUG
+            qDebug("XInput version %d.%d is supported", xiMajor, m_xi2Minor);
+#endif
         }
     }
 }
@@ -118,7 +121,16 @@ void QXcbConnection::xi2Select(xcb_window_t window)
     mask.deviceid = XIAllMasterDevices;
     mask.mask_len = sizeof(bitMask);
     mask.mask = xiBitMask;
-    XISelectEvents(xDisplay, window, &mask, 1);
+    Status result = XISelectEvents(xDisplay, window, &mask, 1);
+    // If we have XInput 2.2 and successfully enable touch on the master
+    // devices, then evdev touchscreens will provide touch only. In most other
+    // cases, there will be emulated mouse events, because true X11 touch
+    // support is so new that for the older drivers, mouse emulation was the
+    // only way; and it's still the fallback even with the modern evdev driver.
+    // But if neither Qt nor X11 does mouse emulation, it will not be possible
+    // to interact with mouse-oriented QWidgets; so we have to let Qt do it.
+    if (m_xi2Minor >= 2 && result == Success)
+        has_touch_without_mouse_emulation = true;
 #endif
 
 #ifndef QT_NO_TABLETEVENT

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -337,4 +337,30 @@ QPlatformTheme *QXcbIntegration::createPlatformTheme(const QString &name) const
     return QGenericUnixTheme::createUnixTheme(name);
 }
 
+QVariant QXcbIntegration::styleHint(QPlatformIntegration::StyleHint hint) const
+{
+    switch (hint) {
+    case QPlatformIntegration::CursorFlashTime:
+    case QPlatformIntegration::KeyboardInputInterval:
+    case QPlatformIntegration::MouseDoubleClickInterval:
+    case QPlatformIntegration::StartDragDistance:
+    case QPlatformIntegration::StartDragTime:
+    case QPlatformIntegration::KeyboardAutoRepeatRate:
+    case QPlatformIntegration::PasswordMaskDelay:
+    case QPlatformIntegration::FontSmoothingGamma:
+    case QPlatformIntegration::StartDragVelocity:
+    case QPlatformIntegration::UseRtlExtensions:
+        // TODO using various xcb, gnome or KDE settings
+        break; // Not implemented, use defaults
+    case QPlatformIntegration::ShowIsFullScreen:
+        // X11 always has support for windows, but the
+        // window manager could prevent it (e.g. matchbox)
+        return false;
+    case QPlatformIntegration::SynthesizeMouseFromTouchEvents:
+        // We do not want Qt to synthesize mouse events if X11 already does it.
+        return m_connections.at(0)->hasTouchWithoutMouseEmulation();
+    }
+    return QPlatformIntegration::styleHint(hint);
+}
+
 QT_END_NAMESPACE

src/plugins/platforms/xcb/qxcbintegration.h

@@ -94,6 +94,7 @@ public:
 
     QStringList themeNames() const;
     QPlatformTheme *createPlatformTheme(const QString &name) const;
+    QVariant styleHint(StyleHint hint) const;
 
     QXcbConnection *defaultConnection() const { return m_connections.first(); }