modlib/minetest/raycast.lua

--+ Raycast wrapper with proper flowingliquid intersections
function raycast(_pos1, _pos2, objects, liquids)
	local raycast = minetest.raycast(_pos1, _pos2, objects, liquids)
	if not liquids then
		return raycast
	end
	local pos1 = modlib.vector.from_minetest(_pos1)
	local _direction = vector.direction(_pos1, _pos2)
	local direction = modlib.vector.from_minetest(_direction)
	local length = vector.distance(_pos1, _pos2)
	local function next()
		for pointed_thing in raycast do
			if pointed_thing.type ~= "node" then
				return pointed_thing
			end
			local _pos = pointed_thing.under
			local pos = modlib.vector.from_minetest(_pos)
			local node = minetest.get_node(_pos)
			local def = minetest.registered_nodes[node.name]
			if not (def and def.drawtype == "flowingliquid") then return pointed_thing end
			local corner_levels = get_liquid_corner_levels(_pos)
			local full_corner_levels = true
			for _, corner_level in pairs(corner_levels) do
				if corner_level[2] < 0.5 then
					full_corner_levels = false
					break
				end
			end
			if full_corner_levels then
				return pointed_thing
			end
			local relative = pos1 - pos
			local inside = true
			for _, prop in pairs(relative) do
				if prop <= -0.5 or prop >= 0.5 then
					inside = false
					break
				end
			end
			local function level(x, z)
				local function distance_squared(corner)
					return (x - corner[1]) ^ 2 + (z - corner[3]) ^ 2
				end
				local irrelevant_corner, distance = 1, distance_squared(corner_levels[1])
				for index = 2, 4 do
					local other_distance = distance_squared(corner_levels[index])
					if other_distance > distance then
						irrelevant_corner, distance = index, other_distance
					end
				end
				local function corner(off)
					return corner_levels[((irrelevant_corner + off) % 4) + 1]
				end
				local base = corner(2)
				local edge_1, edge_2 = corner(1) - base, corner(3) - base
				-- Properly selected edges will have a total length of 2
				assert(math.abs(edge_1[1] + edge_1[3]) + math.abs(edge_2[1] + edge_2[3]) == 2)
				if edge_1[1] == 0 then
					edge_1, edge_2 = edge_2, edge_1
				end
				local level = base[2] + (edge_1[2] * ((x - base[1]) / edge_1[1])) + (edge_2[2] * ((z - base[3]) / edge_2[3]))
				assert(level >= -0.5 and level <= 0.5)
				return level
			end
			inside = inside and (relative[2] < level(relative[1], relative[3]))
			if inside then
				-- pos1 is inside the liquid node
				pointed_thing.intersection_point = _pos1
				pointed_thing.intersection_normal = vector.new(0, 0, 0)
				return pointed_thing
			end
			local function intersection_normal(axis, dir)
				return {x = 0, y = 0, z = 0, [axis] = dir}
			end
			local function plane(axis, dir)
				local offset = dir * 0.5
				local diff_axis = (relative[axis] - offset) / -direction[axis]
				local intersection_point = {}
				for plane_axis = 1, 3 do
					if plane_axis ~= axis then
						local value = direction[plane_axis] * diff_axis + relative[plane_axis]
						if value < -0.5 or value > 0.5 then
							return
						end
						intersection_point[plane_axis] = value
					end
				end
				intersection_point[axis] = offset
				return intersection_point
			end
			if direction[2] > 0 then
				local intersection_point = plane(2, -1)
				if intersection_point then
					pointed_thing.intersection_point = (intersection_point + pos):to_minetest()
					pointed_thing.intersection_normal = intersection_normal("y", -1)
					return pointed_thing
				end
			end
			for coord, other in pairs{[1] = 3, [3] = 1} do
				if direction[coord] ~= 0 then
					local dir = direction[coord] > 0 and -1 or 1
					local intersection_point = plane(coord, dir)
					if intersection_point then
						local height = 0
						for _, corner in pairs(corner_levels) do
							if corner[coord] == dir * 0.5 then
								height = height + (math.abs(intersection_point[other] + corner[other])) * corner[2]
							end
						end
						if intersection_point[2] <= height then
							pointed_thing.intersection_point = (intersection_point + pos):to_minetest()
							pointed_thing.intersection_normal = intersection_normal(modlib.vector.index_aliases[coord], dir)
							return pointed_thing
						end
					end
				end
			end
			for _, triangle in pairs{
				{corner_levels[3], corner_levels[2], corner_levels[1]},
				{corner_levels[4], corner_levels[3], corner_levels[1]}
			} do
				local pos_on_ray = modlib.vector.ray_triangle_intersection(relative, direction, triangle)
				if pos_on_ray and pos_on_ray <= length then
					pointed_thing.intersection_point = (pos1 + modlib.vector.multiply_scalar(direction, pos_on_ray)):to_minetest()
					pointed_thing.intersection_normal = modlib.vector.triangle_normal(triangle):to_minetest()
					return pointed_thing
				end
			end
		end
	end
	return setmetatable({next = next}, {__call = next})
end