Navigate workspace in the main window by dragging the mouse (LMMS#7595)

The scroll bars shown in the main window were removed in favor of a new navigation feature that utilizes dragging the mouse instead. Users can now hold the mouse down on an empty part of the workspace and drag the mouse around to navigate where necessary.

Author: szeli1

include/MainWindow.h

@@ -29,6 +29,7 @@
 #include <QTimer>
 #include <QList>
 #include <QMainWindow>
+#include <QMdiArea>
 
 #include "ConfigManager.h"
 
@@ -57,7 +58,7 @@ class MainWindow : public QMainWindow
 public:
 	QMdiArea* workspace()
 	{
-		return m_workspace;
+		return static_cast<QMdiArea*>(m_workspace);
 	}
 
 	QWidget* toolBar()
@@ -203,7 +204,22 @@ private slots:
 	bool guiSaveProject();
 	bool guiSaveProjectAs( const QString & filename );
 
-	QMdiArea * m_workspace;
+	class MovableQMdiArea : public QMdiArea
+	{
+	public:
+		MovableQMdiArea(QWidget* parent = nullptr);
+		~MovableQMdiArea() {}
+	protected:
+		void mousePressEvent(QMouseEvent* event) override;
+		void mouseMoveEvent(QMouseEvent* event) override;
+		void mouseReleaseEvent(QMouseEvent* event) override;
+	private:
+		bool m_isBeingMoved;
+		int m_lastX;
+		int m_lastY;
+	};
+
+	MovableQMdiArea * m_workspace;
 
 	QWidget * m_toolBar;
 	QGridLayout * m_toolBarLayout;
@@ -258,7 +274,6 @@ private slots:
 
 } ;
 
-
 } // namespace gui
 
 } // namespace lmms

src/gui/MainWindow.cpp

@@ -159,7 +159,7 @@ MainWindow::MainWindow() :
 	sideBar->appendTab(new FileBrowser(root_paths.join("*"), FileItem::defaultFilters(), title,
 		embed::getIconPixmap("computer").transformed(QTransform().rotate(90)), splitter, dirs_as_items));
 
-	m_workspace = new QMdiArea(splitter);
+	m_workspace = new MovableQMdiArea(splitter);
 
 	// Load background
 	emit initProgress(tr("Loading background picture"));
@@ -179,8 +179,8 @@ MainWindow::MainWindow() :
 	}
 
 	m_workspace->setOption( QMdiArea::DontMaximizeSubWindowOnActivation );
-	m_workspace->setHorizontalScrollBarPolicy( Qt::ScrollBarAsNeeded );
-	m_workspace->setVerticalScrollBarPolicy( Qt::ScrollBarAsNeeded );
+	m_workspace->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
+	m_workspace->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
 
 	hbox->addWidget(sideBar);
 	hbox->addWidget(splitter);
@@ -531,8 +531,6 @@ void MainWindow::finalize()
 }
 
 
-
-
 int MainWindow::addWidgetToToolBar( QWidget * _w, int _row, int _col )
 {
 	int col = ( _col == -1 ) ? m_toolBarLayout->columnCount() + 7 : _col;
@@ -944,12 +942,6 @@ void MainWindow::toggleWindow( QWidget *window, bool forceShow )
 		parent->hide();
 		refocus();
 	}
-
-	// Workaround for Qt Bug #260116
-	m_workspace->setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
-	m_workspace->setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
-	m_workspace->setHorizontalScrollBarPolicy( Qt::ScrollBarAsNeeded );
-	m_workspace->setVerticalScrollBarPolicy( Qt::ScrollBarAsNeeded );
 }
 
 
@@ -1601,4 +1593,64 @@ void MainWindow::onProjectFileNameChanged()
 }
 
 
+MainWindow::MovableQMdiArea::MovableQMdiArea(QWidget* parent) :
+	QMdiArea(parent),
+	m_isBeingMoved(false),
+	m_lastX(0),
+	m_lastY(0)
+{}
+
+void MainWindow::MovableQMdiArea::mousePressEvent(QMouseEvent* event)
+{
+	m_lastX = event->x();
+	m_lastY = event->y();
+	m_isBeingMoved = true;
+	setCursor(Qt::ClosedHandCursor);
+}
+
+void MainWindow::MovableQMdiArea::mouseMoveEvent(QMouseEvent* event)
+{
+	if (m_isBeingMoved == false) { return; }
+
+	int minXBoundary = window()->width() - 100;
+	int maxXBoundary = 100;
+	int minYBoundary = window()->height() - 100;
+	int maxYBoundary = 100;
+
+	int minX = minXBoundary;
+	int maxX = maxXBoundary;
+	int minY = minYBoundary;
+	int maxY = maxYBoundary;
+
+	auto subWindows = subWindowList();
+	for (auto* curWindow : subWindows)
+	{
+		if (curWindow->isVisible())
+		{
+			minX = std::min(minX, curWindow->x());
+			maxX = std::max(maxX, curWindow->x() + curWindow->width());
+			minY = std::min(minY, curWindow->y());
+			maxY = std::max(maxY, curWindow->y() + curWindow->height());
+		}
+	}
+
+	int scrollX = m_lastX - event->x();
+	int scrollY = m_lastY - event->y();
+
+	scrollX = scrollX < 0 && minX >= minXBoundary ? 0 : scrollX;
+	scrollX = scrollX > 0 && maxX <= maxXBoundary ? 0 : scrollX;
+	scrollY = scrollY < 0 && minY >= minYBoundary ? 0 : scrollY;
+	scrollY = scrollY > 0 && maxY <= maxYBoundary ? 0 : scrollY;
+
+	scrollContentsBy(-scrollX, -scrollY);
+	m_lastX = event->x();
+	m_lastY = event->y();
+}
+
+void MainWindow::MovableQMdiArea::mouseReleaseEvent(QMouseEvent* event)
+{
+	setCursor(Qt::ArrowCursor);
+	m_isBeingMoved = false;
+}
+
 } // namespace lmms::gui