godot_voxel/terrain/voxel_box_mover.cpp

#include "voxel_box_mover.h"
#include "voxel_map.h"

static AABB expand_with_vector(AABB box, Vector3 v) {

	if (v.x > 0) {
		box.size.x += v.x;
	} else if (v.x < 0) {
		box.position.x += v.x;
		box.size.x -= v.x;
	}

	if (v.y > 0) {
		box.size.y += v.y;
	} else if (v.y < 0) {
		box.position.y += v.y;
		box.size.y -= v.y;
	}

	if (v.z > 0) {
		box.size.z += v.z;
	} else if (v.z < 0) {
		box.position.z += v.z;
		box.size.z -= v.z;
	}

	return box;
}

static float calculate_i_offset(AABB box, AABB other, float motion, int i, int j, int k) {

	const float EPSILON = 0.001;

	Vector3 other_end = other.position + other.size;
	Vector3 box_end = box.position + box.size;

	if (other_end[k] <= box.position[k] || other.position[k] >= box_end[k])
		return motion;

	if (other_end[j] <= box.position[j] || other.position[j] >= box_end[j])
		return motion;

	if (motion > 0.0 && other_end[i] <= box.position[i]) {
		float off = box.position[i] - other_end[i] - EPSILON;
		if (off < motion)
			motion = off;
	}

	if (motion < 0.0 && other.position[i] >= box_end[i]) {
		float off = box_end[i] - other.position[i] + EPSILON;
		if (off > motion)
			motion = off;
	}

	return motion;
}

// Gets the transformed vector for moving a box and slide.
// This algorithm is free from tunnelling for axis-aligned movement,
// except in some high-speed diagonal cases or huge size differences:
// For example, if a box is fast enough to have a diagonal motion jumping from A to B,
// it will pass through C if that other box is the only other one:
//
//  o---o
//  | A |
//  o---o
//          o---o
//          | C |
//          o---o
//                  o---o
//                  | B |
//                  o---o
//
// TODO one way to fix this would be to try a "hot side" projection instead
//
static Vector3 get_motion(AABB box, Vector3 motion, const Vector<AABB> &other_boxes) {
	// The bounding box is expanded to include it's estimated version at next update.
	// This also makes the algorithm tunnelling-free
	AABB expanded_box = expand_with_vector(box, motion);

	Vector<AABB> colliding_boxes;
	for (int i = 0; i < other_boxes.size(); ++i) {
		AABB other = other_boxes[i];
		if (expanded_box.intersects(other_boxes[i]))
			colliding_boxes.push_back(other);
	}

	if (colliding_boxes.size() == 0)
		return motion;

	//print("Colliding: ", colliding_boxes.size())

	Vector3 new_motion = motion;

	for (int i = 0; i < colliding_boxes.size(); ++i)
		new_motion.y = calculate_i_offset(colliding_boxes[i], box, new_motion.y, 1, 0, 2);
	box.position.y += new_motion.y;

	for (int i = 0; i < colliding_boxes.size(); ++i)
		new_motion.x = calculate_i_offset(colliding_boxes[i], box, new_motion.x, 0, 1, 2);
	box.position.x += new_motion.x;

	for (int i = 0; i < colliding_boxes.size(); ++i)
		new_motion.z = calculate_i_offset(colliding_boxes[i], box, new_motion.z, 2, 1, 0);
	box.position.z += new_motion.z;

	return new_motion;
}

Vector3 VoxelBoxMover::get_motion(Vector3 pos, Vector3 motion, AABB aabb, VoxelTerrain *terrain) {

	ERR_FAIL_COND_V(terrain == NULL, Vector3());

	AABB box(aabb.position + pos, aabb.size);
	AABB expanded_box = expand_with_vector(box, motion);

	Vector<AABB> potential_boxes;

	// Collect collisions with the terrain

	Ref<VoxelMap> voxels_ref = terrain->get_map();
	ERR_FAIL_COND_V(voxels_ref.is_null(), Vector3());
	VoxelMap &voxels = **voxels_ref;

	int min_x = int(Math::floor(expanded_box.position.x));
	int min_y = int(Math::floor(expanded_box.position.y));
	int min_z = int(Math::floor(expanded_box.position.z));

	Vector3 expanded_box_end = expanded_box.position + expanded_box.size;
	int max_x = int(Math::ceil(expanded_box_end.x));
	int max_y = int(Math::ceil(expanded_box_end.y));
	int max_z = int(Math::ceil(expanded_box_end.z));

	Vector3i i(min_x, min_y, min_z);

	for (i.z = min_z; i.z < max_z; ++i.z) {
		for (i.y = min_y; i.y < max_y; ++i.y) {
			for (i.x = min_x; i.x < max_x; ++i.x) {

				int voxel_type = voxels.get_voxel(i, 0);
				if (voxel_type != 0) {
					AABB voxel_box = AABB(i.to_vec3(), Vector3(1, 1, 1));
					potential_boxes.push_back(voxel_box);
				}
			}
		}
	}

	// Calculate collisions
	return ::get_motion(box, motion, potential_boxes);
}

Vector3 VoxelBoxMover::_get_motion_binding(Vector3 pos, Vector3 motion, AABB aabb, Node *terrain_node) {
	ERR_FAIL_COND_V(terrain_node == NULL, Vector3());
	VoxelTerrain *terrain = Object::cast_to<VoxelTerrain>(terrain_node);
	ERR_FAIL_COND_V(terrain == NULL, Vector3());
	return get_motion(pos, motion, aabb, terrain);
}

void VoxelBoxMover::_bind_methods() {

	ClassDB::bind_method(D_METHOD("get_motion", "pos", "motion", "aabb", "terrain"), &VoxelBoxMover::_get_motion_binding);
}