Improve getPointedThing() (#4346)

* Improved getPointedThing()

The new algorithm checks every node exactly once.
Now the point and normal vector of the collision is also returned in the
PointedThing (currently they are not used outside of the function).
Now the CNodeDefManager keeps the union of all possible nodeboxes, so
the raycast won't miss any nodes. Also if there are only small
nodeboxes, getPointedThing() is exceptionally fast.
Also adds unit test for VoxelLineIterator.

* Cleanup, code move

This commit moves getPointedThing() and
Client::getSelectedActiveObject() to ClientEnvironment.
The map nodes now can decide which neighbors they are connecting to
(MapNode::getNeighbors()).

1 files changed, 61 insertions, 0 deletions

diff --git a/src/voxelalgorithms.h b/src/voxelalgorithms.h
index 3632546dd..5eff8f7ac 100644
--- a/src/voxelalgorithms.h
+++ b/src/voxelalgorithms.h
@@ -73,7 +73,68 @@ void update_lighting_nodes(
 	std::vector<std::pair<v3s16, MapNode> > &oldnodes,
 	std::map<v3s16, MapBlock*> &modified_blocks);
 
+/*!
+ * This class iterates trough voxels that intersect with
+ * a line. The collision detection does not see nodeboxes,
+ * every voxel is a cube and is returned.
+ * This iterator steps to all nodes exactly once.
+ */
+struct VoxelLineIterator
+{
+public:
+	//! Starting position of the line in world coordinates.
+	v3f m_start_position;
+	//! Direction and length of the line in world coordinates.
+	v3f m_line_vector;
+	/*!
+	 * Each component stores the next smallest positive number, by
+	 * which multiplying the line's vector gives a vector that ends
+	 * on the intersection of two nodes.
+	 */
+	v3f m_next_intersection_multi;
+	/*!
+	 * Each component stores the smallest positive number, by which
+	 * m_next_intersection_multi's components can be increased.
+	 */
+	v3f m_intersection_multi_inc;
+	/*!
+	 * Direction of the line. Each component can be -1 or 1 (if a
+	 * component of the line's vector is 0, then there will be 1).
+	 */
+	v3s16 m_step_directions;
+	//! Position of the current node.
+	v3s16 m_current_node_pos;
+	//! If true, the next node will intersect the line, too.
+	bool m_has_next;
+
+	/*!
+	 * Creates a voxel line iterator with the given line.
+	 * @param start_position starting point of the line
+	 * in voxel coordinates
+	 * @param line_vector    length and direction of the
+	 * line in voxel coordinates. start_position+line_vector
+	 * is the end of the line
+	 */
+	VoxelLineIterator(const v3f &start_position,const v3f &line_vector);
+
+	/*!
+	 * Steps to the next voxel.
+	 * Updates m_current_node_pos and
+	 * m_previous_node_pos.
+	 * Note that it works even if hasNext() is false,
+	 * continuing the line as a ray.
+	 */
+	void next();
+
+	/*!
+	 * Returns true if the next voxel intersects the given line.
+	 */
+	inline bool hasNext() const { return m_has_next; }
+};
+
 } // namespace voxalgo
 
+
+
 #endif