implemented middle click drag on zoomed viewer

ui/viewercontainer.cpp

@@ -24,12 +24,31 @@ ViewerContainer::ViewerContainer(QWidget *parent) :
     setWidget(area);
 
     child = new ViewerWidget(area);
+    child->container = this;
 }
 
 ViewerContainer::~ViewerContainer() {
     delete area;
 }
 
+void ViewerContainer::dragScrollPress(const QPoint &p) {
+    drag_start_x = p.x();
+    drag_start_y = p.y();
+    horiz_start = horizontalScrollBar()->value();
+    vert_start = verticalScrollBar()->value();
+}
+
+void ViewerContainer::dragScrollMove(const QPoint &p) {
+    int true_x = p.x() + (horiz_start - horizontalScrollBar()->value());
+    int true_y = p.y() + (vert_start - verticalScrollBar()->value());
+
+    horizontalScrollBar()->setValue(horizontalScrollBar()->value() + (drag_start_x - true_x));
+    verticalScrollBar()->setValue(verticalScrollBar()->value() + (drag_start_y - true_y));
+
+    drag_start_x = true_x;
+    drag_start_y = true_y;
+}
+
 void ViewerContainer::adjust() {
     if (viewer->seq != NULL) {
         if (child->waveform) {

ui/viewercontainer.h

@@ -15,6 +15,9 @@ public:
     bool fit;
     double zoom;
 
+    void dragScrollPress(const QPoint&);
+    void dragScrollMove(const QPoint&);
+
     Viewer* viewer;
     ViewerWidget* child;
 	void adjust();
@@ -28,6 +31,10 @@ public slots:
 
 private:
     QWidget* area;
+    int drag_start_x;
+    int drag_start_y;
+    int horiz_start;
+    int vert_start;
 };
 
 #endif // VIEWERCONTAINER_H

ui/viewerwidget.cpp

@@ -19,6 +19,7 @@
 #include "ui/collapsiblewidget.h"
 #include "project/undo.h"
 #include "project/media.h"
+#include "ui/viewercontainer.h"
 
 #include <QPainter>
 #include <QAudioOutput>
@@ -215,6 +216,8 @@ void ViewerWidget::move_gizmos(QMouseEvent *event, bool done) {
 void ViewerWidget::mousePressEvent(QMouseEvent* event) {
     if (waveform) {
         seek_from_click(event->x());
+    } else if (event->buttons() & Qt::MiddleButton) {
+        container->dragScrollPress(event->pos());
     } else {
         drag_start_x = event->pos().x();
         drag_start_y = event->pos().y();
@@ -232,9 +235,11 @@ void ViewerWidget::mousePressEvent(QMouseEvent* event) {
 }
 
 void ViewerWidget::mouseMoveEvent(QMouseEvent* event) {
-	if (dragging) {
+    if (dragging) {
 		if (waveform) {
 			seek_from_click(event->x());
+        } else if (event->buttons() & Qt::MiddleButton) {
+            container->dragScrollMove(event->pos());
         } else if (gizmos == NULL) {
 			QDrag* drag = new QDrag(this);
 			QMimeData* mimeData = new QMimeData;

ui/viewerwidget.h

@@ -16,6 +16,7 @@ struct FootageStream;
 class QOpenGLFramebufferObject;
 class Effect;
 class EffectGizmo;
+class ViewerContainer;
 struct GLTextureCoords;
 
 class ViewerWidget : public QOpenGLWidget, QOpenGLFunctions
@@ -27,6 +28,7 @@ public:
     void paintGL();
     void initializeGL();
 	Viewer* viewer;
+    ViewerContainer* container;
 
     QOpenGLFramebufferObject* default_fbo;