Enable block drag (it doesn't do anything yet)

src/qt/widgets/block_grid.cpp

@@ -21,6 +21,11 @@
 #include <QTimer>
 #include <QPixmap>
 #include <QPoint>
+#include <QByteArray>
+#include <QDataStream>
+#include <QMouseEvent>
+#include <QMimeData>
+#include <QDrag>
 #include <algorithm>
 
 namespace duck::widget {
@@ -143,10 +148,71 @@ void BlockGrid::paintEvent (QPaintEvent* event) {
 	}
 }
 
+void BlockGrid::mousePressEvent(QMouseEvent* event) {
+	const auto [icon_index, block_origin]  = locate_icon_index_at(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_icons.size())
+		return;
+
+	QByteArray item_data;
+	QDataStream data_stream(&item_data, QIODevice::WriteOnly);
+	data_stream << m_icons[icon_index_uns].current_frame();
+
+	std::unique_ptr<QMimeData> mime_data(new QMimeData);
+	mime_data->setData("application/x-dndblock", item_data);
+
+	QDrag* const drag(new QDrag(this));
+	drag->setMimeData(mime_data.release());
+	drag->setPixmap(m_icons[icon_index_uns].current_frame());
+	drag->setHotSpot(event->position().toPoint() - block_origin);
+
+	switch (drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction)) {
+	case Qt::MoveAction:
+		break;
+	case Qt::CopyAction:
+		break;
+	default:
+		break;
+	}
+}
+
 void BlockGrid::advance_frame() {
 	for (auto& ico : m_icons) {
 		ico.advance_frame();
 	}
 	this->update();
 }
+
+std::pair<int, QPoint> BlockGrid::locate_icon_index_at(QPoint pt) const {
+	if (pt.x() < g_icon_spacing or pt.y() < g_icon_spacing)
+		return {-1, QPoint()};
+
+	const auto ico_spacing_uns = static_cast<unsigned int>(g_icon_spacing);
+	const auto x = static_cast<unsigned int>(pt.x()) - ico_spacing_uns;
+	const auto y = static_cast<unsigned int>(pt.y()) - ico_spacing_uns;
+	const auto w = static_cast<unsigned int>(m_icon_size.width()) + ico_spacing_uns;
+	const auto h = static_cast<unsigned int>(m_icon_size.height()) + ico_spacing_uns;
+
+	if (x >= w * columns() or y > h * rows())
+		return {-1, QPoint()};
+
+	const unsigned int x_index = x / w;
+	const unsigned int y_index = y / h;
+
+	const auto rel_x = x - x_index * w;
+	const auto rel_y = y - y_index * h;
+
+	if (rel_x < (w - ico_spacing_uns) and rel_y < (h - ico_spacing_uns)) {
+		return {
+			static_cast<int>(x_index + y_index * columns()),
+			QPoint(g_icon_spacing, g_icon_spacing) + pt - QPoint(static_cast<int>(rel_x), static_cast<int>(rel_y))
+		};
+	}
+	else {
+		return {-1, QPoint()};
+	}
+}
 } //namespace duck::widget

src/qt/widgets/block_grid.hpp

@@ -22,6 +22,7 @@
 #include <QPixmap>
 #include <memory>
 #include <vector>
+#include <utility>
 
 class QTimer;
 
@@ -44,6 +45,7 @@ public:
 
 protected:
 	void paintEvent (QPaintEvent* event) override;
+	void mousePressEvent(QMouseEvent* event) override;
 
 private slots:
 	void advance_frame();
@@ -51,6 +53,7 @@ private slots:
 private:
 	unsigned int rows() const;
 	unsigned int columns() const;
+	std::pair<int, QPoint> locate_icon_index_at (QPoint pt) const;
 
 	std::vector<AnimatedPixmap> m_icons;
 	QTimer* m_anim_timer;