Drag&drop, working towards making it accept drop events

Still work in progress

src/qt/widgets/block_grid.cpp

@@ -126,10 +126,26 @@ void BlockGrid::paintEvent (QPaintEvent* event) {
 	}
 }
 
+void BlockGrid::dragEnterEvent(QDragEnterEvent* event) {
+	m_block_dnd.drag_enter_event(event);
+}
+
+void BlockGrid::dropEvent(QDropEvent* event) {
+	m_block_dnd.drop_event(event);
+}
+
 void BlockGrid::mousePressEvent(QMouseEvent* event) {
 	m_block_dnd.mouse_press_event(event);
 }
 
+void BlockGrid::mouseReleaseEvent(QMouseEvent* event) {
+	m_block_dnd.mouse_release_event(event);
+}
+
+void BlockGrid::mouseMoveEvent(QMouseEvent* event) {
+	m_block_dnd.mouse_move_event(event);
+}
+
 void BlockGrid::advance_frame() {
 	for (auto& ico : m_icons) {
 		ico.advance_frame();

src/qt/widgets/block_grid.hpp

@@ -46,7 +46,11 @@ public:
 
 protected:
 	void paintEvent (QPaintEvent* event) override;
+	void dragEnterEvent(QDragEnterEvent* event) override;
+	void dropEvent(QDropEvent* event) override;
 	void mousePressEvent(QMouseEvent* event) override;
+	void mouseReleaseEvent(QMouseEvent* event) override;
+	void mouseMoveEvent(QMouseEvent* event) override;
 
 private slots:
 	void advance_frame();

src/qt/widgets/detail/block_drag_and_drop.cpp

@@ -22,9 +22,13 @@
 #include <QMimeData>
 #include <QDrag>
 #include <QApplication>
+#include <QWidget>
 #include <cassert>
 #include <ciso646>
 #include <memory>
+#if !defined(NDEBUG)
+#	include <iostream>
+#endif
 
 namespace duck::widget::detail {
 namespace {
@@ -32,38 +36,74 @@ constexpr char g_drag_mime[] = "application/x-dndblock";
 } //unnamed namespace
 
 BlockDragAndDrop::BlockDragAndDrop (
-	QObject* parent,
+	QWidget* parent,
 	PointToIndexFunc&& func,
-	std::function<std::size_t()>&& get_block_count,
+	std::function<std::size_t()>&& get_icon_count,
 	std::function<const QPixmap&(std::size_t)>&& get_pixmap
 ) :
 	m_point_to_index(std::move(func)),
-	m_get_block_count(std::move(get_block_count)),
+	m_get_icon_count(std::move(get_icon_count)),
 	m_get_pixmap(std::move(get_pixmap)),
 	m_parent(parent)
 {
 	assert(m_parent);
+	m_parent->setAcceptDrops(true);
 }
 
 void BlockDragAndDrop::mouse_press_event (const QMouseEvent* event) {
-	const auto [icon_index, block_origin]  = m_point_to_index(event->position().toPoint());
-	if (icon_index < 0)
-		return;
-	const auto icon_index_uns = static_cast<std::size_t>(icon_index);
-	if (icon_index_uns >= m_get_block_count())
+	if (event->button() & Qt::LeftButton) {
+		assert(not m_dragging);
+
+		const auto [block_index, block_origin] = m_point_to_index(event->position().toPoint());
+		if (block_index < 0)
+			return;
+
+		const auto icon_index = static_cast<std::size_t>(block_index);
+		if (icon_index >= m_get_icon_count())
+			return;
+
+		m_start_pos = event->position().toPoint();
+		m_dragging = true;
+		m_block_index = block_index;
+		m_hot_spot = m_start_pos - block_origin;
+	}
+}
+
+void BlockDragAndDrop::mouse_release_event(const QMouseEvent* event) {
+	if (event->button() & Qt::LeftButton) {
+		m_dragging = false;
+#if !defined(NDEBUG)
+		std::cout << "Mouse button released before block's drag&drop\n";
+#endif
+	}
+}
+
+void BlockDragAndDrop::mouse_move_event (const QMouseEvent* event) {
+	if (not m_dragging)
 		return;
 
+	if (not (event->buttons() & Qt::LeftButton))
+		return;
+
+	if ((event->position().toPoint() - m_start_pos).manhattanLength() < QApplication::startDragDistance())
+		return;
+
+#if !defined(NDEBUG)
+	std::cout << "mouse_move_event() drag&drop started\n";
+#endif
 	QByteArray item_data;
 	QDataStream data_stream(&item_data, QIODevice::WriteOnly);
-	data_stream << m_get_pixmap(icon_index_uns);
+	data_stream << m_get_pixmap(m_block_index);
 
 	std::unique_ptr<QMimeData> mime_data(new QMimeData);
 	mime_data->setData(g_drag_mime, item_data);
 
+	assert(m_block_index >= 0);
+	const auto icon_index = static_cast<unsigned int>(m_block_index);
 	QDrag* const drag(new QDrag(m_parent));
 	drag->setMimeData(mime_data.release());
-	drag->setPixmap(m_get_pixmap(icon_index_uns));
-	drag->setHotSpot(event->position().toPoint() - block_origin);
+	drag->setPixmap(m_get_pixmap(icon_index));
+	drag->setHotSpot(m_hot_spot);
 
 	switch (drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction)) {
 	case Qt::MoveAction:
@@ -73,5 +113,14 @@ void BlockDragAndDrop::mouse_press_event (const QMouseEvent* event) {
 	default:
 		break;
 	}
+	m_dragging = false;
+}
+
+void BlockDragAndDrop::drag_enter_event(QDragEnterEvent* event) {
+	if (not m_dragging and event->mimeData()->hasFormat(g_drag_mime))
+		event->acceptProposedAction();
+}
+
+void BlockDragAndDrop::drop_event(QDropEvent* event) {
 }
 } //namespace duck::widget::detail

src/qt/widgets/detail/block_drag_and_drop.hpp

@@ -23,6 +23,9 @@
 
 class QMouseEvent;
 class QPixmap;
+class QWidget;
+class QDragEnterEvent;
+class QDropEvent;
 
 namespace duck::widget::detail {
 class BlockDragAndDrop {
@@ -30,19 +33,27 @@ public:
 	typedef std::function<std::pair<int,QPoint>(QPoint)> PointToIndexFunc;
 
 	BlockDragAndDrop (
-		QObject* parent,
+		QWidget* parent,
 		PointToIndexFunc&& func,
-		std::function<std::size_t()>&& get_block_count,
+		std::function<std::size_t()>&& get_icon_count,
 		std::function<const QPixmap&(std::size_t)>&& get_pixmap
 	);
 
 	void mouse_press_event (const QMouseEvent* event);
+	void mouse_release_event (const QMouseEvent* event);
+	void mouse_move_event (const QMouseEvent* event);
+	void drag_enter_event(QDragEnterEvent* event);
+	void drop_event(QDropEvent* event);
 
 private:
 	PointToIndexFunc m_point_to_index;
-	std::function<std::size_t()> m_get_block_count;
+	std::function<std::size_t()> m_get_icon_count;
 	std::function<const QPixmap&(std::size_t)> m_get_pixmap;
-	QObject* m_parent;
+	QWidget* m_parent;
+	QPoint m_start_pos;
+	QPoint m_hot_spot;
+	int m_block_index;
+	bool m_dragging {false};
 };
 
 } //namespace duck::widget::detail