Implement auto-scrolling of the diagram view

2 files changed, 103 insertions, 1 deletions

diff --git a/src/diagramview.cpp b/src/diagramview.cpp
index e2a5779..cb958e4 100644
--- a/src/diagramview.cpp
+++ b/src/diagramview.cpp
@@ -17,6 +17,7 @@
 #include <cmath>
 #include <QMouseEvent>
 #include <QScrollBar>
+#include <QTimer>
 #include <QDebug>
 #include "diagramview.h"
 #include "diagramdocument.h"
@@ -24,12 +25,17 @@
 using namespace std;
 
 DiagramView::DiagramView(QWidget *parent)
-	: QGraphicsView(parent), m_handScrolling(false)
+    : QGraphicsView(parent),
+        m_handScrolling(false),
+        m_autoScrollCount(0),
+        m_autoScrollMargin(16)
 {
 	setAlignment(Qt::AlignLeft | Qt::AlignTop);
 	setRenderHint(QPainter::Antialiasing);
 	setDragMode(QGraphicsView::RubberBandDrag);
 	setRubberBandSelectionMode(Qt::ContainsItemBoundingRect);
+	m_autoScrollTimer = new QTimer(this);
+	connect(m_autoScrollTimer, SIGNAL(timeout()), SLOT(doAutoScroll()));
 }
 
 DiagramDocument *
@@ -80,6 +86,10 @@ DiagramView::mouseMoveEvent(QMouseEvent *event)
 		return;
 	}
 	QGraphicsView::mouseMoveEvent(event);
+
+    if (event->buttons() && !isAutoScrolling() && shouldAutoScroll(event->pos())) {
+        startAutoScroll();
+    }
 }
 
 void
@@ -138,3 +148,85 @@ DiagramView::drawGrid(QPainter *painter, const QRectF &rect)
 	}
 	painter->restore();
 }
+
+static QRect
+clipRect(QWidget *w)
+{
+    if (!w->isVisible())
+        return QRect();
+    QRect r = w->rect();
+    int ox = 0;
+    int oy = 0;
+    while (w
+            && w->isVisible()
+            && !w->isWindow()
+            && w->parentWidget()) {
+        ox -= w->x();
+        oy -= w->y();
+        w = w->parentWidget();
+        r &= QRect(ox, oy, w->width(), w->height());
+    }
+    return r;
+}
+
+void
+DiagramView::startAutoScroll()
+{
+    m_autoScrollTimer->start(50);
+    m_autoScrollCount = 0;
+}
+
+void
+DiagramView::stopAutoScroll()
+{
+    m_autoScrollTimer->stop();
+    m_autoScrollCount = 0;
+}
+
+bool
+DiagramView::isAutoScrolling() const
+{
+    return m_autoScrollTimer->isActive();
+}
+
+bool
+DiagramView::shouldAutoScroll(const QPoint &pos) const
+{
+    QRect area = clipRect(viewport());
+    return (pos.y() - area.top() < m_autoScrollMargin)
+        || (area.bottom() - pos.y() < m_autoScrollMargin)
+        || (pos.x() - area.left() < m_autoScrollMargin)
+        || (area.right() - pos.x() < m_autoScrollMargin);
+}
+
+void
+DiagramView::doAutoScroll()
+{
+    int verticalStep = verticalScrollBar()->pageStep();
+    int horizontalStep = horizontalScrollBar()->pageStep();
+    if (m_autoScrollCount < qMax(verticalStep, horizontalStep))
+        ++m_autoScrollCount;
+
+    int verticalValue = verticalScrollBar()->value();
+    int horizontalValue = horizontalScrollBar()->value();
+
+    QPoint pos = viewport()->mapFromGlobal(QCursor::pos());
+    QRect area = clipRect(viewport());
+
+    if (pos.y() - area.top() < m_autoScrollMargin)
+        verticalScrollBar()->setValue(verticalValue - m_autoScrollCount);
+    else if (area.bottom() - pos.y() < m_autoScrollMargin)
+        verticalScrollBar()->setValue(verticalValue + m_autoScrollCount);
+    if (pos.x() - area.left() < m_autoScrollMargin)
+        horizontalScrollBar()->setValue(horizontalValue - m_autoScrollCount);
+    else if (area.right() - pos.x() < m_autoScrollMargin)
+        horizontalScrollBar()->setValue(horizontalValue + m_autoScrollCount);
+
+    bool verticalUnchanged = (verticalValue == verticalScrollBar()->value());
+    bool horizontalUnchanged = (horizontalValue == horizontalScrollBar()->value());
+    if (verticalUnchanged && horizontalUnchanged) {
+        stopAutoScroll();
+    } else {
+        viewport()->update();
+    }
+}
diff --git a/src/diagramview.h b/src/diagramview.h
index 9e57c36..1a16f6b 100644
--- a/src/diagramview.h
+++ b/src/diagramview.h
@@ -19,6 +19,7 @@
 
 #include <QGraphicsView>
 class DiagramDocument;
+class QTimer;
 
 class DiagramView : public QGraphicsView
 {
@@ -41,13 +42,22 @@ protected:
 
 protected slots:
 	void updateSceneRect2(const QRectF &rect);
+	void doAutoScroll();
 
 private:
+    void startAutoScroll();
+    void stopAutoScroll();
+    bool isAutoScrolling() const;
+    bool shouldAutoScroll(const QPoint &pos) const;
+
 	bool m_handScrolling;
 	QPoint m_handScrollingOrigin;
 	QCursor m_savedCursor;
 	int m_handScrollingValueX;
 	int m_handScrollingValueY;
+	QTimer *m_autoScrollTimer;
+	int m_autoScrollCount;
+	int m_autoScrollMargin;
 };
 
 #endif