QLineEdit: implement quick text selection by mouse

This is a standard feature in GtkEntry widgets or HTML
<input type="text"> elements. During a normal text selection by mouse
(LeftButton press + mouse move event), it's now possible to quickly
select all the text from the start of the selection to the end
of the line edit by moving the mouse cursor down.
By moving it up instead, all the text up to the start of the line edit
gets selected. If the layout direction is right-to-left, the semantic of
the mouse movement is inverted.

This feature is only enabled if the y() of the mouse move event is
bigger than a fixed threshold, to avoid unexpected selections in the
normal case. This threshold is set by the QPlatformTheme and a value
smaller than zero disables this feature.

The threshold is updated whenever the style or the screen changes.

[ChangeLog][QtWidgets][QLineEdit] Implemented quick text selection by
mouse in QLineEdit.

Change-Id: I4de33c2d11c033ec295de2b2ea81adf786324f4b
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/gui/kernel/qplatformintegration.cpp

@@ -418,6 +418,8 @@ QVariant QPlatformIntegration::styleHint(StyleHint hint) const
         return QPlatformTheme::defaultThemeHint(QPlatformTheme::UiEffects);
     case WheelScrollLines:
         return QPlatformTheme::defaultThemeHint(QPlatformTheme::WheelScrollLines);
+    case MouseQuickSelectionThreshold:
+        return QPlatformTheme::defaultThemeHint(QPlatformTheme::MouseQuickSelectionThreshold);
     }
 
     return 0;

src/gui/kernel/qplatformintegration.h

@@ -164,6 +164,7 @@ public:
         UiEffects,
         WheelScrollLines,
         ShowShortcutsInContextMenus,
+        MouseQuickSelectionThreshold
     };
 
     virtual QVariant styleHint(StyleHint hint) const;

src/gui/kernel/qplatformtheme.cpp

@@ -559,6 +559,8 @@ QVariant QPlatformTheme::defaultThemeHint(ThemeHint hint)
                 dist = defaultThemeHint(MouseDoubleClickDistance).toInt(&ok) * 2;
             return QVariant(ok ? dist : 10);
         }
+    case MouseQuickSelectionThreshold:
+        return QVariant(10);
     }
     return QVariant();
 }

src/gui/kernel/qplatformtheme.h

@@ -117,7 +117,8 @@ public:
         WheelScrollLines,
         TouchDoubleTapDistance,
         ShowShortcutsInContextMenus,
-        IconFallbackSearchPaths
+        IconFallbackSearchPaths,
+        MouseQuickSelectionThreshold
     };
 
     enum DialogType {

src/gui/kernel/qstylehints.cpp

@@ -79,6 +79,7 @@ public:
         , m_tabFocusBehavior(-1)
         , m_uiEffects(-1)
         , m_wheelScrollLines(-1)
+        , m_mouseQuickSelectionThreshold(-1)
         {}
 
     int m_mouseDoubleClickInterval;
@@ -90,6 +91,7 @@ public:
     int m_tabFocusBehavior;
     int m_uiEffects;
     int m_wheelScrollLines;
+    int m_mouseQuickSelectionThreshold;
 };
 
 /*!
@@ -537,4 +539,38 @@ void QStyleHints::setWheelScrollLines(int scrollLines)
     emit wheelScrollLinesChanged(scrollLines);
 }
 
+/*!
+    Sets the mouse quick selection threshold.
+    \internal
+    \sa mouseQuickSelectionThreshold()
+    \since 5.11
+*/
+void QStyleHints::setMouseQuickSelectionThreshold(int threshold)
+{
+    Q_D(QStyleHints);
+    if (d->m_mouseQuickSelectionThreshold == threshold)
+        return;
+    d->m_mouseQuickSelectionThreshold = threshold;
+    emit mouseDoubleClickIntervalChanged(threshold);
+}
+
+/*!
+    \property QStyleHints::mouseQuickSelectionThreshold
+    \brief Quick selection mouse threshold in QLineEdit.
+
+    This property defines how much the mouse cursor should be moved along the y axis
+    to trigger a quick selection during a normal QLineEdit text selection.
+
+    If the property value is less than or equal to 0, the quick selection feature is disabled.
+
+    \since 5.11
+*/
+int QStyleHints::mouseQuickSelectionThreshold() const
+{
+    Q_D(const QStyleHints);
+    if (d->m_mouseQuickSelectionThreshold >= 0)
+        return d->m_mouseQuickSelectionThreshold;
+    return themeableHint(QPlatformTheme::MouseQuickSelectionThreshold, QPlatformIntegration::MouseQuickSelectionThreshold).toInt();
+}
+
 QT_END_NAMESPACE

src/gui/kernel/qstylehints.h

@@ -73,6 +73,7 @@ class Q_GUI_EXPORT QStyleHints : public QObject
     Q_PROPERTY(bool singleClickActivation READ singleClickActivation STORED false CONSTANT FINAL)
     Q_PROPERTY(bool useHoverEffects READ useHoverEffects WRITE setUseHoverEffects NOTIFY useHoverEffectsChanged FINAL)
     Q_PROPERTY(int wheelScrollLines READ wheelScrollLines NOTIFY wheelScrollLinesChanged FINAL)
+    Q_PROPERTY(int mouseQuickSelectionThreshold READ mouseQuickSelectionThreshold WRITE setMouseQuickSelectionThreshold NOTIFY mouseQuickSelectionThresholdChanged FINAL)
 
 public:
     void setMouseDoubleClickInterval(int mouseDoubleClickInterval);
@@ -104,6 +105,8 @@ public:
     void setUseHoverEffects(bool useHoverEffects);
     int wheelScrollLines() const;
     void setWheelScrollLines(int scrollLines);
+    void setMouseQuickSelectionThreshold(int threshold);
+    int mouseQuickSelectionThreshold() const;
 
 Q_SIGNALS:
     void cursorFlashTimeChanged(int cursorFlashTime);
@@ -115,6 +118,7 @@ Q_SIGNALS:
     void tabFocusBehaviorChanged(Qt::TabFocusBehavior tabFocusBehavior);
     void useHoverEffectsChanged(bool useHoverEffects);
     void wheelScrollLinesChanged(int scrollLines);
+    void mouseQuickSelectionThresholdChanged(int threshold);
 
 private:
     friend class QGuiApplication;

src/widgets/widgets/qlineedit.cpp

@@ -1466,6 +1466,8 @@ bool QLineEdit::event(QEvent * e)
 #endif
     } else if (e->type() == QEvent::Resize) {
         d->positionSideWidgets();
+    } else if (e->type() == QEvent::StyleChange) {
+        d->initMouseYThreshold();
     }
 #ifdef QT_KEYPAD_NAVIGATION
     if (QApplication::keypadNavigationEnabled()) {
@@ -1546,7 +1548,17 @@ void QLineEdit::mouseMoveEvent(QMouseEvent * e)
             const bool select = (d->imHints & Qt::ImhNoPredictiveText);
 #endif
 #ifndef QT_NO_IM
-            if (d->control->composeMode() && select) {
+            if (d->mouseYThreshold > 0 && e->pos().y() > d->mousePressPos.y() + d->mouseYThreshold) {
+                if (layoutDirection() == Qt::RightToLeft)
+                    d->control->home(select);
+                else
+                    d->control->end(select);
+            } else if (d->mouseYThreshold > 0 && e->pos().y() + d->mouseYThreshold < d->mousePressPos.y()) {
+                if (layoutDirection() == Qt::RightToLeft)
+                    d->control->end(select);
+                else
+                    d->control->home(select);
+            } else if (d->control->composeMode() && select) {
                 int startPos = d->xToPos(d->mousePressPos.x());
                 int currentPos = d->xToPos(e->pos().x());
                 if (startPos != currentPos)

src/widgets/widgets/qlineedit_p.cpp

@@ -56,6 +56,7 @@
 #endif
 #include <qpainter.h>
 #include <qpropertyanimation.h>
+#include <qstylehints.h>
 #include <qvalidator.h>
 
 QT_BEGIN_NAMESPACE
@@ -232,6 +233,13 @@ void QLineEditPrivate::init(const QString& txt)
     q->setAcceptDrops(true);
 
     q->setAttribute(Qt::WA_MacShowFocusRect);
+
+    initMouseYThreshold();
+}
+
+void QLineEditPrivate::initMouseYThreshold()
+{
+    mouseYThreshold = QGuiApplication::styleHints()->mouseQuickSelectionThreshold();
 }
 
 QRect QLineEditPrivate::adjustedContentsRect() const

src/widgets/widgets/qlineedit_p.h

@@ -141,7 +141,7 @@ public:
         dragEnabled(0), clickCausedFocus(0), hscroll(0), vscroll(0),
         alignment(Qt::AlignLeading | Qt::AlignVCenter),
         leftTextMargin(0), topTextMargin(0), rightTextMargin(0), bottomTextMargin(0),
-        lastTextSize(0)
+        lastTextSize(0), mouseYThreshold(0)
     {
     }
 
@@ -155,6 +155,7 @@ public:
     QPointer<QAction> selectAllAction;
 #endif
     void init(const QString&);
+    void initMouseYThreshold();
 
     QRect adjustedControlRect(const QRect &) const;
 
@@ -253,6 +254,7 @@ private:
     SideWidgetEntryList leadingSideWidgets;
     SideWidgetEntryList trailingSideWidgets;
     int lastTextSize;
+    int mouseYThreshold;
 };
 Q_DECLARE_TYPEINFO(QLineEditPrivate::SideWidgetEntry, Q_PRIMITIVE_TYPE);
 Q_DECLARE_TYPEINFO(QLineEditPrivate::SideWidgetLocation, Q_PRIMITIVE_TYPE);

tests/auto/widgets/widgets/qlineedit/tst_qlineedit.cpp

@@ -67,6 +67,8 @@
 #include "../../../shared/platforminputcontext.h"
 #include <private/qinputmethod_p.h>
 
+Q_LOGGING_CATEGORY(lcTests, "qt.widgets.tests")
+
 QT_BEGIN_NAMESPACE
 class QPainter;
 QT_END_NAMESPACE
@@ -300,8 +302,8 @@ private slots:
     void shortcutOverrideOnReadonlyLineEdit_data();
     void shortcutOverrideOnReadonlyLineEdit();
     void QTBUG59957_clearButtonLeftmostAction();
-
     void QTBUG_60319_setInputMaskCheckImSurroundingText();
+    void testQuickSelectionWithMouse();
 
 protected slots:
     void editingFinished();
@@ -4699,5 +4701,90 @@ void tst_QLineEdit::QTBUG_60319_setInputMaskCheckImSurroundingText()
     QCOMPARE(surroundingText.length(), cursorPosition);
 }
 
+void tst_QLineEdit::testQuickSelectionWithMouse()
+{
+    const auto text = QStringLiteral("This is quite a long line of text.");
+    const auto prefix = QStringLiteral("Th");
+    const auto suffix = QStringLiteral("t.");
+    QVERIFY(text.startsWith(prefix));
+    QVERIFY(text.endsWith(suffix));
+
+    QLineEdit lineEdit;
+    lineEdit.setText(text);
+    lineEdit.show();
+
+    const QPoint center = lineEdit.contentsRect().center();
+
+    // Normal mouse selection from left to right, y doesn't change.
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(20, 0));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(!lineEdit.selectedText().isEmpty());
+    QVERIFY(!lineEdit.selectedText().endsWith(suffix));
+
+    // Normal mouse selection from left to right, y change is below threshold.
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(20, 5));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(!lineEdit.selectedText().isEmpty());
+    QVERIFY(!lineEdit.selectedText().endsWith(suffix));
+
+    // Normal mouse selection from right to left, y doesn't change.
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(-20, 0));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(!lineEdit.selectedText().isEmpty());
+    QVERIFY(!lineEdit.selectedText().startsWith(prefix));
+
+    // Normal mouse selection from right to left, y change is below threshold.
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(-20, -5));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(!lineEdit.selectedText().isEmpty());
+    QVERIFY(!lineEdit.selectedText().startsWith(prefix));
+
+    const int offset = QGuiApplication::styleHints()->mouseQuickSelectionThreshold() + 1;
+
+    // Select the whole right half.
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(1, offset));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(lineEdit.selectedText().endsWith(suffix));
+
+    // Select the whole left half.
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(1, -offset));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(lineEdit.selectedText().startsWith(prefix));
+
+    // Normal selection -> quick selection -> back to normal selection.
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(20, 0));
+    const auto partialSelection = lineEdit.selectedText();
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(!partialSelection.endsWith(suffix));
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(20, offset));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+    QVERIFY(lineEdit.selectedText().endsWith(suffix));
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(20, 0));
+    qCDebug(lcTests) << "Selected text:" << lineEdit.selectedText();
+#ifdef Q_PROCESSOR_ARM
+    QEXPECT_FAIL("", "Currently fails on gcc-armv7, needs investigation.", Continue);
+#endif
+    QCOMPARE(lineEdit.selectedText(), partialSelection);
+
+    lineEdit.setLayoutDirection(Qt::RightToLeft);
+
+    // Select the whole left half (RTL layout).
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(1, offset));
+    QVERIFY(lineEdit.selectedText().startsWith(prefix));
+
+    // Select the whole right half (RTL layout).
+    QTest::mousePress(lineEdit.windowHandle(), Qt::LeftButton, Qt::NoModifier, center);
+    QTest::mouseMove(lineEdit.windowHandle(), center + QPoint(1, -offset));
+    QVERIFY(lineEdit.selectedText().endsWith(suffix));
+}
+
 QTEST_MAIN(tst_QLineEdit)
 #include "tst_qlineedit.moc"