allow user to zoom in/out Web page

1. Mouse wheel with Ctrl pressing will zoom in/out the Markdown Web
page;
2. Ctrl+-, Ctrl++ will zoom in/out the Markdown Web page;
3. Ctrl+0 recover the Web page zoom factor to 1.

src/dialog/vsettingsdialog.cpp

@@ -2,10 +2,9 @@
 #include <QtWidgets>
 #include "vconfigmanager.h"
 #include "utils/vutils.h"
+#include "vconstants.h"
 
 extern VConfigManager vconfig;
-static const qreal c_webZoomFactorMax = 5;
-static const qreal c_webZoomFactorMin = 0.25;
 
 VSettingsDialog::VSettingsDialog(QWidget *p_parent)
     : QDialog(p_parent)

src/resources/markdown_template.js

@@ -35,6 +35,14 @@ var scrollToAnchor = function(anchor) {
     }
 };
 
+window.onwheel = function(e) {
+    e = e || window.event;
+    var ctrl = !!e.ctrlKey;
+    if (ctrl) {
+        e.preventDefault();
+    }
+}
+
 window.onscroll = function() {
     var scrollTop = document.documentElement.scrollTop || document.body.scrollTop || window.pageYOffset;
     var eles = document.querySelectorAll("h1, h2, h3, h4, h5, h6");
@@ -129,7 +137,7 @@ document.onkeydown = function(e) {
         return;
 
     default:
-        content.keyPressEvent(key);
+        content.keyPressEvent(key, ctrl, shift);
         keyState = 0;
         return;
     }

src/vconstants.h

@@ -5,4 +5,7 @@ enum class DocType { Html, Markdown };
 enum class ClipboardOpType { Invalid, CopyFile, CopyDir };
 enum class OpenFileMode {Read = 0, Edit};
 
+static const qreal c_webZoomFactorMax = 5;
+static const qreal c_webZoomFactorMin = 0.25;
+
 #endif

src/vdocument.cpp

@@ -55,7 +55,7 @@ void VDocument::setLog(const QString &p_log)
     emit logChanged(p_log);
 }
 
-void VDocument::keyPressEvent(int p_key)
+void VDocument::keyPressEvent(int p_key, bool p_ctrl, bool p_shift)
 {
-    emit keyPressed(p_key);
+    emit keyPressed(p_key, p_ctrl, p_shift);
 }

src/vdocument.h

@@ -24,7 +24,7 @@ public slots:
     void setToc(const QString &toc);
     void setHeader(const QString &anchor);
     void setLog(const QString &p_log);
-    void keyPressEvent(int p_key);
+    void keyPressEvent(int p_key, bool p_ctrl, bool p_shift);
     void updateText();
 
 signals:
@@ -34,7 +34,7 @@ signals:
     void headerChanged(const QString &anchor);
     void htmlChanged(const QString &html);
     void logChanged(const QString &p_log);
-    void keyPressed(int p_key);
+    void keyPressed(int p_key, bool p_ctrl, bool p_shift);
 
 private:
     QString m_toc;

src/vedittab.cpp

@@ -17,6 +17,7 @@
 #include "vmdedit.h"
 #include "dialog/vfindreplacedialog.h"
 #include "veditarea.h"
+#include "vconstants.h"
 
 extern VConfigManager vconfig;
 
@@ -592,16 +593,67 @@ bool VEditTab::checkToc()
     return ret;
 }
 
-void VEditTab::handleWebKeyPressed(int p_key)
+void VEditTab::handleWebKeyPressed(int p_key, bool p_ctrl, bool /* p_shift */)
 {
+    Q_ASSERT(webPreviewer);
     switch (p_key) {
     // Esc
     case 27:
         m_editArea->getFindReplaceDialog()->closeDialog();
         break;
 
+    // Dash
+    case 189:
+        if (p_ctrl) {
+            // Zoom out.
+            zoomWebPage(false);
+        }
+        break;
+
+    // Equal
+    case 187:
+        if (p_ctrl) {
+            // Zoom in.
+            zoomWebPage(true);
+        }
+        break;
+
+    // 0
+    case 48:
+        if (p_ctrl) {
+            // Recover zoom.
+            webPreviewer->setZoomFactor(1);
+        }
+        break;
+
     default:
         break;
     }
 }
 
+void VEditTab::wheelEvent(QWheelEvent *p_event)
+{
+    if (!isEditMode && webPreviewer) {
+        QPoint angle = p_event->angleDelta();
+        Qt::KeyboardModifiers modifiers = p_event->modifiers();
+        if (!angle.isNull() && (angle.y() != 0) && (modifiers & Qt::ControlModifier)) {
+            zoomWebPage(angle.y() > 0);
+            p_event->accept();
+            return;
+        }
+    }
+    p_event->ignore();
+}
+
+void VEditTab::zoomWebPage(bool p_zoomIn, qreal p_step)
+{
+    Q_ASSERT(webPreviewer);
+    qreal curFactor = webPreviewer->zoomFactor();
+    qreal newFactor = p_zoomIn ? curFactor + p_step : curFactor - p_step;
+    if (newFactor < c_webZoomFactorMin) {
+        newFactor = c_webZoomFactorMin;
+    } else if (newFactor > c_webZoomFactorMax) {
+        newFactor = c_webZoomFactorMax;
+    }
+    webPreviewer->setZoomFactor(newFactor);
+}

src/vedittab.h

@@ -51,6 +51,9 @@ public:
     QString getSelectedText() const;
     void clearSearchedWordHighlight();
 
+protected:
+    void wheelEvent(QWheelEvent *p_event) Q_DECL_OVERRIDE;
+
 signals:
     void getFocused();
     void outlineChanged(const VToc &toc);
@@ -65,7 +68,7 @@ private slots:
     void updateTocFromHeaders(const QVector<VHeader> &headers);
     void handleTextChanged();
     void noticeStatusChanged();
-    void handleWebKeyPressed(int p_key);
+    void handleWebKeyPressed(int p_key, bool p_ctrl, bool p_shift);
 
 private:
     void setupUI();
@@ -83,6 +86,7 @@ private:
     // Check if @tableOfContent is outdated (such as renaming the file).
     // Return true if we need to update toc.
     bool checkToc();
+    void zoomWebPage(bool p_zoomIn, qreal p_step = 0.25);
 
     QPointer<VFile> m_file;
     bool isEditMode;