renderer: Fix lock of resource reads in hud render entity.

libopenage/renderer/stages/hud/object.cpp

@@ -38,8 +38,15 @@ void HudDragObject::fetch_updates(const time::time_t &time) {
 
 	// Get data from render entity
 	this->drag_start = this->render_entity->get_drag_start();
+
+	// Thread-safe access to curves needs a lock on the render entity's mutex
+	auto read_lock = this->render_entity->get_read_lock();
+
 	this->drag_pos.sync(this->render_entity->get_drag_pos() /* , this->last_update */);
 
+	// Unlock the render entity mutex
+	read_lock.unlock();
+
 	// Set self to changed so that world renderer can update the renderable
 	this->changed = true;
 	this->render_entity->clear_changed_flag();

libopenage/renderer/stages/hud/render_entity.cpp

@@ -24,10 +24,14 @@ void DragRenderEntity::update(const coord::input drag_pos,
 }
 
 const curve::Continuous<coord::input> &DragRenderEntity::get_drag_pos() {
+	std::shared_lock lock{this->mutex};
+
 	return this->drag_pos;
 }
 
-const coord::input &DragRenderEntity::get_drag_start() {
+const coord::input DragRenderEntity::get_drag_start() {
+	std::shared_lock lock{this->mutex};
+
 	return this->drag_start;
 }
 

libopenage/renderer/stages/hud/render_entity.h

@@ -28,6 +28,8 @@ class DragRenderEntity final : public renderer::RenderEntity {
 	 * Update the render entity with information from the gamestate
 	 * or input system.
 	 *
+	 * Updating the render entity with this method is thread-safe.
+	 *
 	 * @param drag_pos Position of the dragged corner.
 	 * @param time Current simulation time.
 	 */
@@ -37,16 +39,21 @@ class DragRenderEntity final : public renderer::RenderEntity {
 	/**
 	 * Get the position of the dragged corner.
 	 *
+	 * Accessing the drag position curve REQUIRES a read lock on the render entity
+	 * (using \p get_read_lock()) to ensure thread safety.
+	 *
 	 * @return Coordinates of the dragged corner.
 	 */
 	const curve::Continuous<coord::input> &get_drag_pos();
 
 	/**
 	 * Get the position of the start corner.
 	 *
+	 * Accessing the drag start is thread-safe.
+	 *
 	 * @return Coordinates of the start corner.
 	 */
-	const coord::input &get_drag_start();
+	const coord::input get_drag_start();
 
 private:
 	/**