Allow the platform to specify a press and hold delay.

Press and hold is an interaction available on many platforms,
particularly when touch is involved. In Qt Quick this is exposed to the
user via MouseArea::onPressAndHold. This value should not be hard-coded,
but rather use a platform-specified default. This commit adds the
low-level hooks necessary for that to happen.

Task-number: QTBUG-24793
Change-Id: I621a8ac9de66b881e34336228056bffbb6306a70
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

src/gui/kernel/qplatformintegration.cpp

@@ -359,6 +359,8 @@ QVariant QPlatformIntegration::styleHint(StyleHint hint) const
         return true;
     case SetFocusOnTouchRelease:
         return QVariant(false);
+    case MousePressAndHoldInterval:
+        return QPlatformTheme::defaultThemeHint(QPlatformTheme::MousePressAndHoldInterval);
     }
 
     return 0;

src/gui/kernel/qplatformintegration.h

@@ -148,7 +148,8 @@ public:
         SynthesizeMouseFromTouchEvents,
         PasswordMaskCharacter,
         SetFocusOnTouchRelease,
-        ShowIsMaximized
+        ShowIsMaximized,
+        MousePressAndHoldInterval
     };
 
     virtual QVariant styleHint(StyleHint hint) const;

src/gui/kernel/qplatformtheme.cpp

@@ -79,6 +79,9 @@ QT_BEGIN_NAMESPACE
     \value MouseDoubleClickInterval (int) Mouse double click interval in ms,
                                     overriding QPlatformIntegration::styleHint.
 
+    \value MousePressAndHoldInterval (int) Mouse press and hold interval in ms,
+                                    overriding QPlatformIntegration::styleHint.
+
     \value StartDragDistance (int) Start drag distance,
                              overriding QPlatformIntegration::styleHint.
 
@@ -423,6 +426,8 @@ QVariant QPlatformTheme::themeHint(ThemeHint hint) const
         return QGuiApplicationPrivate::platformIntegration()->styleHint(QPlatformIntegration::PasswordMaskDelay);
     case QPlatformTheme::PasswordMaskCharacter:
         return QGuiApplicationPrivate::platformIntegration()->styleHint(QPlatformIntegration::PasswordMaskCharacter);
+    case QPlatformTheme::MousePressAndHoldInterval:
+        return QGuiApplicationPrivate::platformIntegration()->styleHint(QPlatformIntegration::MousePressAndHoldInterval);
     default:
         return QPlatformTheme::defaultThemeHint(hint);
     }
@@ -488,6 +493,8 @@ QVariant QPlatformTheme::defaultThemeHint(ThemeHint hint)
         return QVariant::fromValue(QList<int>());
     case DialogSnapToDefaultButton:
         return QVariant(false);
+    case MousePressAndHoldInterval:
+        return QVariant(800);
     }
     return QVariant();
 }

src/gui/kernel/qplatformtheme.h

@@ -106,7 +106,8 @@ public:
         TabAllWidgets,
         IconPixmapSizes,
         PasswordMaskCharacter,
-        DialogSnapToDefaultButton
+        DialogSnapToDefaultButton,
+        MousePressAndHoldInterval
     };
 
     enum DialogType {

src/gui/kernel/qstylehints.cpp

@@ -127,6 +127,17 @@ int QStyleHints::mouseDoubleClickInterval() const
            themeableHint(QPlatformTheme::MouseDoubleClickInterval, QPlatformIntegration::MouseDoubleClickInterval).toInt();
 }
 
+/*!
+    Returns the time limit in milliseconds that activates
+    a press and hold.
+
+    \since 5.3
+*/
+int QStyleHints::mousePressAndHoldInterval() const
+{
+    return themeableHint(QPlatformTheme::MousePressAndHoldInterval, QPlatformIntegration::MousePressAndHoldInterval).toInt();
+}
+
 /*!
     Sets the \a startDragDistance.
     \internal

src/gui/kernel/qstylehints.h

@@ -57,6 +57,7 @@ class Q_GUI_EXPORT QStyleHints : public QObject
 public:
     void setMouseDoubleClickInterval(int mouseDoubleClickInterval);
     int mouseDoubleClickInterval() const;
+    int mousePressAndHoldInterval() const;
     void setStartDragDistance(int startDragDistance);
     int startDragDistance() const;
     void setStartDragTime(int startDragTime);

tests/manual/qpainfo/main.cpp

@@ -180,7 +180,8 @@ int main(int argc, char **argv)
               << " startDragVelocity=" << styleHints->startDragVelocity() << " keyboardInputInterval=" << styleHints->keyboardInputInterval()
               << " keyboardAutoRepeatRate=" << styleHints->keyboardAutoRepeatRate() << " cursorFlashTime=" << styleHints->cursorFlashTime()
               << " showIsFullScreen=" << styleHints->showIsFullScreen() << " passwordMaskDelay=" << styleHints->passwordMaskDelay()
-              << " fontSmoothingGamma=" << styleHints->fontSmoothingGamma() << " useRtlExtensions=" << styleHints->useRtlExtensions() << '\n';
+              << " fontSmoothingGamma=" << styleHints->fontSmoothingGamma() << " useRtlExtensions=" << styleHints->useRtlExtensions()
+              << " mousePressAndHoldInterval=" << styleHints->mousePressAndHoldInterval() << '\n';
 
     const QPlatformTheme *platformTheme = QGuiApplicationPrivate::platformTheme();
     std::cout << "\nTheme:\n  Styles: " << platformTheme->themeHint(QPlatformTheme::StyleNames).toStringList();