PointInConcavePolygon (日本語)

この関数は与えられた多角形の内部に対して指定地点があるならば true を返します。

function pointInPolygon(pgon, tx, ty)
	if (#pgon < 6) then
		return false
	end
 
	local x1 = pgon[#pgon - 1]
	local y1 = pgon[#pgon]
	local cur_quad = getQuad(tx,ty,x1,y1)
	local next_quad
	local total = 0
	local i
 
	for i = 1,#pgon,2 do
		local x2 = pgon[i]
		local y2 = pgon[i+1]
		next_quad = getQuad(tx,ty,x2,y2)
		local diff = next_quad - cur_quad
 
		if (diff == 2) or (diff == -2) then
			if (x2 - (((y2 - ty) * (x1 - x2)) / (y1 - y2))) < tx then
				diff = -diff
			end
		elseif diff == 3 then
			diff = -1
		elseif diff == -3 then
			diff = 1
		end
 
		total = total + diff
		cur_quad = next_quad
		x1 = x2
		y1 = y2
	end
 
	return (math.abs(total)==4)
end
 
function getQuad(axis_x,axis_y,vert_x,vert_y)
	if vert_x < axis_x then
		if vert_y < axis_y then
			return 1
		else
			return 4
		end
	else
		if vert_y < axis_y then
			return 2
		else
			return 3
		end	
	end
end

用例:

function love.load()
	poly = {69,119,371,39,724,140,751,491,572,222,420,163,283,232,236,338,399,401,540,446,371,508,195,503,96,327}
	color = {255,255,255}
end
 
function love.update(dt)
	if pointInPolygon(poly, love.mouse.getX(), love.mouse.getY()) then
		color = {0,255,0}
	else
		color = {255,255,255}
	end
end
 
function love.draw()
	if #poly >= 6 then
		love.graphics.setColor(color)
		love.graphics.polygon("line",poly)
	end
end
 
-- こちらへ pointInPolygon および getQuad 関数を追加します。