Implement 2D bresenham line drawing for #35

We need it to be 3D though.
We essentially just ported f51f153459/src/index.js to Lua, as https://medium.com/geekculture/bresenhams-line-drawing-algorithm-2e0e953901b3 was WRONG as it didn't handle all edge cases and this one is much more optimised.

bresenham.lua

@@ -0,0 +1,157 @@
+local Vector3 = dofile("worldeditadditions/utils/vector3.lua")
+
+local function make_grid(size)
+	local grid = {}
+	
+	for y=1,size.y do
+		for x=1,size.x do
+			grid[(size.x * y) + x] = 0
+		end
+	end
+	
+	return {
+		size = size,
+		data = grid
+	}
+end
+
+local function index(grid, pos)
+	return (grid.size.x * pos.y) + pos.x
+end
+
+local function grid_to_string(grid)
+	local result = {}
+	for y=1,grid.size.y do
+		for x=1,grid.size.x do
+			local i = index(grid, Vector3.new(x, y))
+			if grid.data[i] == 0 then
+				table.insert(result, "#")
+			elseif grid.data[i] == 1 then
+				table.insert(result, " ")
+			elseif grid.data[i] < 10 then
+				table.insert(result, tostring(grid.data[i]))
+			else
+				table.insert(result, "?")
+			end
+		end
+		table.insert(result, "\n")
+	end
+	
+	return table.concat(result, "")
+end
+
+--- Draws a line using Bresenham's algorithm in 2d.
+-- Implemented ported from https://github.com/anushaihalapathirana/Bresenham-line-drawing-algorithm/blob/f51f153459a1656bfb1f433edc75e6644a052bb2/src/index.js
+-- @param	grid	Grid	The grid to draw on.
+-- @param	pos1	Vector3	The starting point of the line.
+-- @param	pos2	Vector3	The ending point of the line.
+-- @param	value	number	The number to fill in grid cells we draw in.
+-- @returns	void
+local function draw_line_2d(grid, pos1, pos2, value)
+	if not value then value = 1 end
+	
+	if pos1 == pos2 then
+		grid.data[index(grid, pos1)] = value
+		return
+	end
+	
+	grid.data[index(grid, pos1)] = value -- plot pos1
+	local delta = pos2 - pos1
+	local absdelta = delta:abs()
+	local delta_error = (2 * absdelta.y) - absdelta.x -- d
+	if absdelta.x <= absdelta.y then delta_error = (2 * absdelta.x) - absdelta.y end
+	
+	local pos_current = pos1:clone()
+	local steps = 0
+	
+	local limit = absdelta.y
+	if absdelta.x > absdelta.y then limit = absdelta.x end
+	
+	for _=1,limit do
+		local do_x = false
+		local do_y = false
+		if absdelta.x > absdelta.y then
+			do_x = true
+			if delta_error < 0 then
+				delta_error = delta_error + 2*absdelta.y
+			else
+				do_y = true
+				delta_error = delta_error + (2*absdelta.y - 2*absdelta.x)
+			end
+		else
+			do_y = true
+			if delta_error < 0 then
+				delta_error = delta_error + 2*absdelta.x
+			else
+				do_x = true
+				delta_error = delta_error + (2*absdelta.x) - (2*absdelta.y)
+			end
+		end
+		
+		
+		if do_x then
+			local acc = 1
+			if delta.x < 0 then acc = -1 end
+			pos_current.x = pos_current.x + acc
+		end
+		if do_y then
+			local acc = 1
+			if delta.y < 0 then acc = -1 end
+			pos_current.y = pos_current.y + acc
+		end
+				
+		local i = index(grid, pos_current)
+		grid.data[i] = value
+		steps = steps + 1
+	end
+end
+
+local size = Vector3.new(120, 40)
+local grid = make_grid(size)
+
+
+
+-- draw_line_2d(grid, Vector3.new(10, 10), Vector3.new(40, 10))
+-- draw_line_2d(grid, Vector3.new(70, 10), Vector3.new(70, 10))
+draw_line_2d(grid, Vector3.new(75, 10), Vector3.new(75, 40))
+draw_line_2d(grid, Vector3.new(80, 40), Vector3.new(80, 10))
+
+-- local centre = Vector3.new(25, 25)
+-- draw_line_2d(grid, centre, Vector3.new(0, 0))
+-- draw_line_2d(grid, centre, Vector3.new(5, 0))
+-- draw_line_2d(grid, centre, Vector3.new(10, 0))
+-- draw_line_2d(grid, centre, Vector3.new(15, 0))
+-- draw_line_2d(grid, centre, Vector3.new(20, 0))
+-- draw_line_2d(grid, centre, Vector3.new(25, 0))
+-- draw_line_2d(grid, centre, Vector3.new(30, 0), 3)
+
+for i=1,9 do
+	print("LINE", i)
+	local pos1 = Vector3.new(
+		math.random(0, size.x),
+		math.random(0, size.y)
+	)
+	local pos2 = Vector3.new(
+		math.random(0, size.x),
+		math.random(0, size.y)
+	)
+	draw_line_2d(grid, pos1, pos2)
+end
+-- draw_line_2d(grid,
+-- 	Vector3.new(3, 4),
+-- 	Vector3.new(8, 9)
+-- )
+-- draw_line_2d(grid,
+-- 	Vector3.new(10, 9),
+-- 	Vector3.new(15, 4)
+-- )
+-- draw_line_2d(grid,
+-- 	Vector3.new(20, 10),
+-- 	Vector3.new(40, 20)
+-- )
+-- draw_line_2d(grid,
+-- 	Vector3.new(10, 9),
+-- 	Vector3.new(55, 4)
+-- )
+
+print(grid_to_string(grid))