Reimplemented Pathfinder to use A* instead of spawning an entity

#closes 788

features/pathfinder/luafinding.lua

@@ -0,0 +1,146 @@
+
+-- Positions must be a table (or metatable) where table.x and table.y are accessible.
+
+local FindVector = require( "features.pathfinder.find_vector" )
+local Heap = require( "features.pathfinder.heap" )
+
+local Luafinding = {}
+Luafinding.__index = Luafinding
+
+-- This instantiates a new Luafinding class for usage later.
+-- "start" and "finish" should both be 2 dimensional FindVectors, or just a table with "x" and "y" keys. See the note at the top of this file.
+-- positionOpenCheck can be a function or a table.
+-- If it's a function it must have a return value of true or false depending on whether or not the position is open.
+-- If it's a table it should simply be a table of values such as "pos[x][y] = true".
+function Luafinding:Initialize( start, finish, positionOpenCheck )
+    local newPath = setmetatable( { Start = FindVector(start.Y,start.X), Finish = FindVector(finish.Y,finish.X), PositionOpenCheck = positionOpenCheck }, Luafinding )
+    newPath:CalculatePath()
+    return newPath
+end
+
+local function distance( start, finish )
+    local dx = start.x - finish.x
+    local dy = start.y - finish.y
+    return dx * dx + dy * dy
+end
+
+local positionIsOpen
+local function positionIsOpenTable( pos, check ) return check[pos.x] and check[pos.x][pos.y] end
+local function positionIsOpenCustom( pos, check ) return check( _, pos ) end
+
+local adjacentPositions = {
+    FindVector( 0, -1 ),
+    FindVector( -1, 0 ),
+    FindVector( 0, 1 ),
+    FindVector( 1, 0 ),
+}
+
+local function fetchOpenAdjacentNodes( pos, positionOpenCheck )
+    local result = {}
+
+    for i = 1, #adjacentPositions do
+        local adjacentPos = pos + adjacentPositions[i]
+        if positionIsOpen( adjacentPos, positionOpenCheck ) then
+            table.insert( result, adjacentPos )
+        end
+    end
+
+    return result
+end
+
+-- This is the function used to actually calculate the path.
+-- It returns the calcated path table, or nil if it cannot find a path.
+function Luafinding:CalculatePath()
+    local start, finish, positionOpenCheck = self.Start, self.Finish, self.PositionOpenCheck
+    if not positionOpenCheck then return end
+    positionIsOpen = type( positionOpenCheck ) == "table" and positionIsOpenTable or positionIsOpenCustom
+    if not positionIsOpen( finish, positionOpenCheck ) then return end
+    -- EID edit: check if end position is surrounded by stuff and therefore unaccessable. This is done for a quick early out
+    local directlyAdjacents = fetchOpenAdjacentNodes( self.Finish, positionOpenCheck )
+    if #directlyAdjacents == 0 then return end
+    -- edit end
+    local open, closed = Heap(), {}
+
+    start.gScore = 0
+    start.hScore = distance( start, finish )
+    start.fScore = start.hScore
+
+    open.Compare = function( a, b )
+        return a.fScore < b.fScore
+    end
+
+    open:Push( start )
+
+    while not open:Empty() do
+        local current = open:Pop()
+        local currentId = current:ID()
+        if not closed[currentId] then
+            if current == finish then
+                local path = {}
+                while true do
+                    if current.previous then
+                        table.insert( path, 1, current )
+                        current = current.previous
+                    else
+                        table.insert( path, 1, start )
+                        self.Path = path
+                        return path
+                    end
+                end
+            end
+
+            closed[currentId] = true
+
+            local adjacents = fetchOpenAdjacentNodes( current, positionOpenCheck )
+            for i = 1, #adjacents do
+                local adjacent = adjacents[i]
+                if not closed[adjacent:ID()] then
+                    local added_gScore = current.gScore + distance( current, adjacent )
+
+                    if not adjacent.gScore or added_gScore < adjacent.gScore then
+                        adjacent.gScore = added_gScore
+                        if not adjacent.hScore then
+                            adjacent.hScore = distance( adjacent, finish )
+                        end
+                        adjacent.fScore = added_gScore + adjacent.hScore
+
+                        open:Push( adjacent )
+                        adjacent.previous = current
+                    end
+                end
+            end
+        end
+    end
+end
+
+function Luafinding:GetPath()
+    return self.Path
+end
+
+function Luafinding:GetDistance()
+    local path = self.Path
+    if not path then return end
+    return distance( path[1], path[#path] )
+end
+
+function Luafinding:GetTiles()
+    local path = self.Path
+    if not path then return end
+    return #path
+end
+
+function Luafinding:__tostring()
+    local path = self.Path
+    local string = ""
+
+    if path then
+        for k, v in ipairs( path ) do
+            local formatted = ( k .. ": " .. v )
+            string = k == 1 and formatted or string .. "\n" .. formatted
+        end
+    end
+
+    return string
+end
+
+return setmetatable( Luafinding, { __call = function( self, ... ) return self:Initialize( ... ) end } )