Support vertical drag scrolling on document blank areas

Author: indy256

src/pdfselection.cpp

@@ -112,6 +112,7 @@ QPair<int, int> PdfView::selectionRange(int page, int count) const {
 }
 
 void PdfView::clearSelection() {
+    scrollDragPending = scrollDragging = false;
     selectionScrollTimer.stop();
     selecting = selectionVisible = false;
     selectionAnchor = selectionEnd = {};

src/pdfview.cpp

@@ -434,13 +434,16 @@ void PdfView::followLink(const LinkTarget &target) {
 
 void PdfView::updateLinkCursor() {
     const auto point = viewport()->mapFromGlobal(QCursor::pos());
-    if (selecting && selectionVisible) viewport()->setCursor(Qt::IBeamCursor);
+    if (scrollDragging) viewport()->setCursor(Qt::ClosedHandCursor);
+    else if (selecting && selectionVisible) viewport()->setCursor(Qt::IBeamCursor);
     else if (!viewport()->rect().contains(point)) viewport()->unsetCursor();
     else viewport()->setCursor(linkAt(point).valid() ? Qt::PointingHandCursor
         : textAt(point).valid() ? Qt::IBeamCursor : Qt::ArrowCursor);
 }
 
 void PdfView::hideEvent(QHideEvent *event) {
+    scrollDragPending = scrollDragging = false;
+    viewport()->unsetCursor();
     selectionScrollTimer.stop();
     selecting = false;
     pressedLink = {};
@@ -449,6 +452,16 @@ void PdfView::hideEvent(QHideEvent *event) {
 
 void PdfView::mouseMoveEvent(QMouseEvent *event) {
     selectionPointer = event->position().toPoint();
+    if (scrollDragPending) {
+        if (qAbs(selectionPointer.y() - pressPosition.y()) > QApplication::startDragDistance())
+            scrollDragging = true;
+        if (scrollDragging) {
+            verticalScrollBar()->setValue(scrollDragStart + pressPosition.y() - selectionPointer.y());
+            viewport()->setCursor(Qt::ClosedHandCursor);
+        }
+        event->accept();
+        return;
+    }
     if ((selectionPointer - pressPosition).manhattanLength() > QApplication::startDragDistance()) {
         pressedLink = {};
         if (selecting) {
@@ -482,6 +495,13 @@ void PdfView::mousePressEvent(QMouseEvent *event) {
         selectionAnchor = selectionEnd = textAt(pressPosition);
         selecting = selectionAnchor.valid();
         pressedLink = linkAt(pressPosition);
+        const QPoint documentPoint = pressPosition
+            + QPoint(horizontalScrollBar()->value(), verticalScrollBar()->value());
+        scrollDragPending = !selecting && !pressedLink.valid()
+            && std::any_of(pages.cbegin(), pages.cend(), [&](const QRectF &page) {
+                return page.contains(documentPoint);
+            });
+        scrollDragStart = verticalScrollBar()->value();
         event->accept();
         return;
     }
@@ -490,6 +510,9 @@ void PdfView::mousePressEvent(QMouseEvent *event) {
 
 void PdfView::mouseReleaseEvent(QMouseEvent *event) {
     if (event->button() == Qt::LeftButton) {
+        const bool wasScrollDragging = scrollDragging;
+        scrollDragPending = scrollDragging = false;
+        if (wasScrollDragging) updateLinkCursor();
         selectionScrollTimer.stop();
         if (selecting && selectionVisible) {
             selectionPointer = event->position().toPoint();

src/pdfview.h

@@ -105,6 +105,9 @@ class PdfView : public QAbstractScrollArea {
     QTimer selectionScrollTimer;
     LinkTarget pressedLink;
     QPoint pressPosition;
+    bool scrollDragPending = false;
+    bool scrollDragging = false;
+    int scrollDragStart = 0;
     EpubDestinations epubDestinations;
     struct Match { int page; QVector<QRectF> rectangles; }; // Normalized display coordinates.
     QVector<Match> matches;

tests/viewer_tests.cpp

@@ -66,6 +66,57 @@ private slots:
         QApplication::setFont(QFont(QFontDatabase::applicationFontFamilies(fontId).first(), 10));
     }
     void cleanupTestCase() { FPDF_DestroyLibrary(); }
+    void documentDragScrolling() {
+        QTemporaryDir directory;
+        const auto path = directory.filePath("drag.pdf");
+        {
+            QPdfWriter writer(path);
+            QPainter painter(&writer);
+            painter.fillRect(QRect(0, 0, 100, 100), Qt::red);
+        }
+        PdfView view;
+        view.resize(700, 450);
+        view.show();
+        QString error;
+        QVERIFY2(view.open(path, {}, &error), qPrintable(error));
+        view.setZoom(1.0);
+        QTest::qWait(20);
+        auto bar = view.verticalScrollBar();
+        QVERIFY(bar->maximum() > 200);
+        bar->setValue(0);
+        const QPoint start(view.viewport()->width() / 2, 250);
+        QTest::mousePress(view.viewport(), Qt::LeftButton, Qt::NoModifier, start);
+        QTest::mouseMove(view.viewport(), start - QPoint(0, 2));
+        QCOMPARE(bar->value(), 0);
+        QTest::mouseMove(view.viewport(), start + QPoint(30, -100));
+        QCOMPARE(bar->value(), 100);
+        QCOMPARE(view.horizontalScrollBar()->value(), 0);
+        QCOMPARE(view.viewport()->cursor().shape(), Qt::ClosedHandCursor);
+        QVERIFY(!view.hasSelection());
+        QTest::mouseMove(view.viewport(), start - QPoint(0, 40));
+        QCOMPARE(bar->value(), 40);
+        QTest::mouseRelease(view.viewport(), Qt::LeftButton, Qt::NoModifier, start - QPoint(0, 40));
+        QVERIFY(view.viewport()->cursor().shape() != Qt::ClosedHandCursor);
+        QTest::mouseMove(view.viewport(), start);
+        QCOMPARE(bar->value(), 40);
+
+        // Background margins and right-button drags must not pan the document.
+        for (const auto button : {Qt::LeftButton, Qt::RightButton}) {
+            const QPoint origin = button == Qt::LeftButton ? QPoint(5, 250) : start;
+            QTest::mousePress(view.viewport(), button, Qt::NoModifier, origin);
+            QTest::mouseMove(view.viewport(), origin - QPoint(0, 80));
+            QTest::mouseRelease(view.viewport(), button, Qt::NoModifier, origin - QPoint(0, 80));
+            QCOMPARE(bar->value(), 40);
+        }
+        QTest::mousePress(view.viewport(), Qt::LeftButton, Qt::NoModifier, start);
+        QTest::mouseMove(view.viewport(), start - QPoint(0, 80));
+        QCOMPARE(bar->value(), 120);
+        view.hide();
+        view.show();
+        QTest::mouseMove(view.viewport(), start);
+        QCOMPARE(bar->value(), 120);
+        QTest::mouseRelease(view.viewport(), Qt::LeftButton, Qt::NoModifier, start);
+    }
     void textSelection_data() {
         QTest::addColumn<int>("rotation");
         for (int rotation : {0, 90, 180, 270})