dragging mouse with Ctrl and left button pressed to scroll in read and edit mode

src/resources/markdown_template.js

@@ -449,3 +449,62 @@ var handleToc = function(needToc) {
     }
 };
 
+// Implement mouse drag with Ctrl and left button pressed to scroll.
+var vds_oriMouseClientX = 0;
+var vds_oriMouseClientY = 0;
+var vds_readyToScroll = false;
+var vds_scrolled = false;
+
+window.onmousedown = function(e) {
+    e = e || window.event;
+    // Left button and Ctrl key.
+    if (e.buttons == 1
+        && e.ctrlKey
+        && window.getSelection().rangeCount == 0) {
+        vds_oriMouseClientX = e.clientX;
+        vds_oriMouseClientY = e.clientY;
+        vds_readyToScroll = true;
+        vds_scrolled = false;
+        e.preventDefault();
+    } else {
+        vds_readyToScroll = false;
+        vds_scrolled = false;
+    }
+};
+
+window.onmouseup = function(e) {
+    e = e || window.event;
+    if (vds_scrolled || vds_readyToScroll) {
+        // Have been scrolled, restore the cursor style.
+        document.body.style.cursor = "auto";
+        e.preventDefault();
+    }
+
+    vds_readyToScroll = false;
+    vds_scrolled = false;
+};
+
+window.onmousemove = function(e) {
+    e = e || window.event;
+    if (vds_readyToScroll) {
+        deltaX = e.clientX - vds_oriMouseClientX;
+        deltaY = e.clientY - vds_oriMouseClientY;
+
+        var threshold = 5;
+        if (Math.abs(deltaX) >= threshold || Math.abs(deltaY) >= threshold) {
+            vds_oriMouseClientX = e.clientX;
+            vds_oriMouseClientY = e.clientY;
+
+            if (!vds_scrolled) {
+                vds_scrolled = true;
+                document.body.style.cursor = "all-scroll";
+            }
+
+            var scrollX = -deltaX;
+            var scrollY = -deltaY;
+            window.scrollBy(scrollX, scrollY);
+        }
+
+        e.preventDefault();
+    }
+};

src/vedit.cpp

@@ -711,3 +711,73 @@ VEditConfig &VEdit::getConfig()
 {
     return m_config;
 }
+
+void VEdit::mousePressEvent(QMouseEvent *p_event)
+{
+    if (p_event->button() == Qt::LeftButton
+        && p_event->modifiers() == Qt::ControlModifier
+        && !textCursor().hasSelection()) {
+        m_oriMouseX = p_event->x();
+        m_oriMouseY = p_event->y();
+        m_readyToScroll = true;
+        m_mouseMoveScrolled = false;
+        p_event->accept();
+        return;
+    }
+
+    m_readyToScroll = false;
+    m_mouseMoveScrolled = false;
+
+    QTextEdit::mousePressEvent(p_event);
+}
+
+void VEdit::mouseReleaseEvent(QMouseEvent *p_event)
+{
+    if (m_mouseMoveScrolled || m_readyToScroll) {
+        viewport()->setCursor(Qt::IBeamCursor);
+        m_readyToScroll = false;
+        m_mouseMoveScrolled = false;
+        p_event->accept();
+        return;
+    }
+
+    m_readyToScroll = false;
+    m_mouseMoveScrolled = false;
+
+    QTextEdit::mouseReleaseEvent(p_event);
+}
+
+void VEdit::mouseMoveEvent(QMouseEvent *p_event)
+{
+    const int threshold = 5;
+
+    if (m_readyToScroll) {
+        int deltaX = p_event->x() - m_oriMouseX;
+        int deltaY = p_event->y() - m_oriMouseY;
+
+        if (qAbs(deltaX) >= threshold || qAbs(deltaY) >= threshold) {
+            m_oriMouseX = p_event->x();
+            m_oriMouseY = p_event->y();
+
+            if (!m_mouseMoveScrolled) {
+                m_mouseMoveScrolled = true;
+                viewport()->setCursor(Qt::SizeAllCursor);
+            }
+
+            QScrollBar *verBar = verticalScrollBar();
+            QScrollBar *horBar = horizontalScrollBar();
+            if (verBar->isVisible()) {
+                verBar->setValue(verBar->value() - deltaY);
+            }
+
+            if (horBar->isVisible()) {
+                horBar->setValue(horBar->value() - deltaX);
+            }
+        }
+
+        p_event->accept();
+        return;
+    }
+
+    QTextEdit::mouseMoveEvent(p_event);
+}

src/vedit.h

@@ -110,6 +110,11 @@ protected:
     virtual void updateFontAndPalette();
     virtual void contextMenuEvent(QContextMenuEvent *p_event) Q_DECL_OVERRIDE;
 
+    // Used to implement dragging mouse with Ctrl and left button pressed to scroll.
+    virtual void mousePressEvent(QMouseEvent *p_event) Q_DECL_OVERRIDE;
+    virtual void mouseReleaseEvent(QMouseEvent *p_event) Q_DECL_OVERRIDE;
+    virtual void mouseMoveEvent(QMouseEvent *p_event) Q_DECL_OVERRIDE;
+
     // Update m_config according to VConfigManager.
     void updateConfig();
 
@@ -128,6 +133,11 @@ private:
     // Timer for extra selections highlight.
     QTimer *m_highlightTimer;
 
+    bool m_readyToScroll;
+    bool m_mouseMoveScrolled;
+    int m_oriMouseX;
+    int m_oriMouseY;
+
     void showWrapLabel();
 
     // Trigger the timer to request highlight.