Support clicking to toggle checkboxes in QTextEdit

Add QAbstractTextDocumentLayout::markerAt(pos) for hit testing.
(Qt Quick TextEdit needs it too.) Finds out whether the position
corresponds to a marker on a paragraph.  I.e. it finds checkboxes in
GitHub-flavored markdown.  This enables editor classes to toggle
checkboxes by clicking them.

Use it in QTextEdit to add the checkbox toggling feature.  Also show the
"pointing finger" cursor when hovering a toggleable checkbox.

Change-Id: I036c967ab45e14c836272eac2cc7c7d652543c89
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

src/gui/text/qabstracttextdocumentlayout.cpp

@@ -41,6 +41,7 @@
 #include <qtextformat.h>
 #include "qtextdocument_p.h"
 #include "qtextengine_p.h"
+#include "qtextlist.h"
 
 #include "qabstracttextdocumentlayout_p.h"
 
@@ -649,6 +650,36 @@ QTextFormat QAbstractTextDocumentLayout::formatAt(const QPointF &pos) const
     return pieceTable->formatCollection()->format(it->format);
 }
 
+/*!
+    \since 5.14
+
+    Returns the block (probably a list item) whose \l{QTextBlockFormat::marker()}{marker}
+    is found at the given position \a pos.
+*/
+QTextBlock QAbstractTextDocumentLayout::blockWithMarkerAt(const QPointF &pos) const
+{
+    QTextBlock block = document()->firstBlock();
+    while (block.isValid()) {
+        if (block.blockFormat().marker() != QTextBlockFormat::NoMarker) {
+            QRectF blockBr = blockBoundingRect(block);
+            QTextBlockFormat blockFmt = block.blockFormat();
+            QFontMetrics fm(block.charFormat().font());
+            qreal totalIndent = blockFmt.indent() + blockFmt.leftMargin() + blockFmt.textIndent();
+            if (block.textList())
+                totalIndent += block.textList()->format().indent() * 40;
+            QRectF adjustedBr = blockBr.adjusted(totalIndent - fm.height(), 0, totalIndent - blockBr.width(), fm.height() - blockBr.height());
+            if (adjustedBr.contains(pos)) {
+                //qDebug() << "hit block" << block.text() << blockBr << adjustedBr << "marker" << block.blockFormat().marker()
+                //         << "font" << block.charFormat().font() << "adj" << lineHeight << totalIndent;
+                if (block.blockFormat().hasProperty(QTextFormat::BlockMarker))
+                    return block;
+            }
+        }
+        block = block.next();
+    }
+    return QTextBlock();
+}
+
 /*!
     \fn QRectF QAbstractTextDocumentLayout::frameBoundingRect(QTextFrame *frame) const
 

src/gui/text/qabstracttextdocumentlayout.h

@@ -87,6 +87,7 @@ public:
     QString anchorAt(const QPointF& pos) const;
     QString imageAt(const QPointF &pos) const;
     QTextFormat formatAt(const QPointF &pos) const;
+    QTextBlock blockWithMarkerAt(const QPointF &pos) const;
 
     virtual int pageCount() const = 0;
     virtual QSizeF documentSize() const = 0;

src/widgets/widgets/qtextedit.cpp

@@ -167,6 +167,7 @@ void QTextEditPrivate::init(const QString &html)
     QObject::connect(control, SIGNAL(copyAvailable(bool)), q, SIGNAL(copyAvailable(bool)));
     QObject::connect(control, SIGNAL(selectionChanged()), q, SIGNAL(selectionChanged()));
     QObject::connect(control, SIGNAL(cursorPositionChanged()), q, SLOT(_q_cursorPositionChanged()));
+    QObject::connect(control, SIGNAL(blockMarkerHovered(QTextBlock)), q, SLOT(_q_hoveredBlockWithMarkerChanged(QTextBlock)));
 
     QObject::connect(control, SIGNAL(textChanged()), q, SLOT(updateMicroFocus()));
 
@@ -187,6 +188,7 @@ void QTextEditPrivate::init(const QString &html)
     vbar->setSingleStep(20);
 
     viewport->setBackgroundRole(QPalette::Base);
+    q->setMouseTracking(true);
     q->setAcceptDrops(true);
     q->setFocusPolicy(Qt::StrongFocus);
     q->setAttribute(Qt::WA_KeyCompression);
@@ -228,6 +230,21 @@ void QTextEditPrivate::_q_cursorPositionChanged()
 #endif
 }
 
+void QTextEditPrivate::_q_hoveredBlockWithMarkerChanged(const QTextBlock &block)
+{
+    Q_Q(QTextEdit);
+    Qt::CursorShape cursor = cursorToRestoreAfterHover;
+    if (block.isValid() && !q->isReadOnly()) {
+        QTextBlockFormat::MarkerType marker = block.blockFormat().marker();
+        if (marker != QTextBlockFormat::NoMarker) {
+            if (viewport->cursor().shape() != Qt::PointingHandCursor)
+                cursorToRestoreAfterHover = viewport->cursor().shape();
+            cursor = Qt::PointingHandCursor;
+        }
+    }
+    viewport->setCursor(cursor);
+}
+
 void QTextEditPrivate::pageUpDown(QTextCursor::MoveOperation op, QTextCursor::MoveMode moveMode)
 {
     QTextCursor cursor = control->textCursor();

src/widgets/widgets/qtextedit.h

@@ -331,6 +331,7 @@ private:
     Q_PRIVATE_SLOT(d_func(), void _q_adjustScrollbars())
     Q_PRIVATE_SLOT(d_func(), void _q_ensureVisible(const QRectF &))
     Q_PRIVATE_SLOT(d_func(), void _q_cursorPositionChanged())
+    Q_PRIVATE_SLOT(d_func(), void _q_hoveredBlockWithMarkerChanged(const QTextBlock &))
     friend class QTextEditControl;
     friend class QTextDocument;
     friend class QWidgetTextControl;

src/widgets/widgets/qtextedit_p.h

@@ -104,6 +104,7 @@ public:
 
     void _q_currentCharFormatChanged(const QTextCharFormat &format);
     void _q_cursorPositionChanged();
+    void _q_hoveredBlockWithMarkerChanged(const QTextBlock &block);
 
     void updateDefaultTextOption();
 
@@ -136,6 +137,8 @@ public:
 
     QString placeholderText;
 
+    Qt::CursorShape cursorToRestoreAfterHover = Qt::IBeamCursor;
+
 #ifdef QT_KEYPAD_NAVIGATION
     QBasicTimer deleteAllTimer;
 #endif

src/widgets/widgets/qwidgettextcontrol.cpp

@@ -1581,6 +1581,11 @@ void QWidgetTextControlPrivate::mousePressEvent(QEvent *e, Qt::MouseButton butto
             e->ignore();
             return;
     }
+    bool wasValid = blockWithMarkerUnderMouse.isValid();
+    blockWithMarkerUnderMouse = q->blockWithMarkerAt(pos);
+    if (wasValid != blockWithMarkerUnderMouse.isValid())
+        emit q->blockMarkerHovered(blockWithMarkerUnderMouse);
+
 
     cursorIsFocusIndicator = false;
     const QTextCursor oldSelection = cursor;
@@ -1599,6 +1604,8 @@ void QWidgetTextControlPrivate::mousePressEvent(QEvent *e, Qt::MouseButton butto
         selectedBlockOnTrippleClick = cursor;
 
         anchorOnMousePress = QString();
+        blockWithMarkerUnderMouse = QTextBlock();
+        emit q->blockMarkerHovered(blockWithMarkerUnderMouse);
 
         trippleClickTimer.stop();
     } else {
@@ -1738,6 +1745,11 @@ void QWidgetTextControlPrivate::mouseMoveEvent(QEvent *e, Qt::MouseButton button
         }
         selectionChanged(true);
         repaintOldAndNewSelection(oldSelection);
+    } else {
+        bool wasValid = blockWithMarkerUnderMouse.isValid();
+        blockWithMarkerUnderMouse = q->blockWithMarkerAt(mousePos);
+        if (wasValid != blockWithMarkerUnderMouse.isValid())
+            emit q->blockMarkerHovered(blockWithMarkerUnderMouse);
     }
 
     sendMouseEventToInputContext(e, QEvent::MouseMove, button, mousePos, modifiers, buttons, globalPos);
@@ -1787,6 +1799,26 @@ void QWidgetTextControlPrivate::mouseReleaseEvent(QEvent *e, Qt::MouseButton but
         emit q->microFocusChanged();
     }
 
+    // toggle any checkbox that the user clicks
+    if ((interactionFlags & Qt::TextEditable) && (button & Qt::LeftButton) &&
+            (blockWithMarkerUnderMouse.isValid()) && !cursor.hasSelection()) {
+        QTextBlock markerBlock = q->blockWithMarkerAt(pos);
+        if (markerBlock == blockWithMarkerUnderMouse) {
+            auto fmt = blockWithMarkerUnderMouse.blockFormat();
+            switch (fmt.marker()) {
+            case QTextBlockFormat::Unchecked :
+                fmt.setMarker(QTextBlockFormat::Checked);
+                break;
+            case QTextBlockFormat::Checked:
+                fmt.setMarker(QTextBlockFormat::Unchecked);
+                break;
+            default:
+                break;
+            }
+            cursor.setBlockFormat(fmt);
+        }
+    }
+
     if (interactionFlags & Qt::LinksAccessibleByMouse) {
         if (!(button & Qt::LeftButton))
             return;
@@ -2385,6 +2417,12 @@ QString QWidgetTextControl::anchorAtCursor() const
     return d->anchorForCursor(d->cursor);
 }
 
+QTextBlock QWidgetTextControl::blockWithMarkerAt(const QPointF &pos) const
+{
+    Q_D(const QWidgetTextControl);
+    return d->doc->documentLayout()->blockWithMarkerAt(pos);
+}
+
 bool QWidgetTextControl::overwriteMode() const
 {
     Q_D(const QWidgetTextControl);

src/widgets/widgets/qwidgettextcontrol_p.h

@@ -150,6 +150,8 @@ public:
 
     QString anchorAtCursor() const;
 
+    QTextBlock blockWithMarkerAt(const QPointF &pos) const;
+
     bool overwriteMode() const;
     void setOverwriteMode(bool overwrite);
 
@@ -242,6 +244,7 @@ Q_SIGNALS:
     void microFocusChanged();
     void linkActivated(const QString &link);
     void linkHovered(const QString &);
+    void blockMarkerHovered(const QTextBlock &block);
     void modificationChanged(bool m);
 
 public:

src/widgets/widgets/qwidgettextcontrol_p_p.h

@@ -55,6 +55,7 @@
 #include "QtGui/qtextdocumentfragment.h"
 #include "QtGui/qtextcursor.h"
 #include "QtGui/qtextformat.h"
+#include "QtGui/qtextobject.h"
 #if QT_CONFIG(menu)
 #include "QtWidgets/qmenu.h"
 #endif
@@ -227,6 +228,7 @@ public:
 
     QString highlightedAnchor; // Anchor below cursor
     QString anchorOnMousePress;
+    QTextBlock blockWithMarkerUnderMouse;
     bool hadSelectionOnMousePress;
 
     bool ignoreUnusedNavigationEvents;