Lua点在多边形：射线法的内外判定

local function inside(px, py, poly)
    local count = 0
    for i = 1, #poly do
        local j = i % #poly + 1
        if (poly[i][2] > py) ~= (poly[j][2] > py) then
            count = count + 1     -- 只数跨越不比横坐标
        end
    end
    return count % 2 == 1         -- 点在右侧时结果反转
end

local function inside(px, py, poly)
    local count = 0
    for i = 1, #poly do
        local j = i % #poly + 1
        local y1, y2 = poly[i][2], poly[j][2]
        if (y1 > py) ~= (y2 > py) then
            local x1, x2 = poly[i][1], poly[j][1]
            local cx = x1 + (py - y1) * (x2 - x1) / (y2 - y1)
            if cx > px then count = count + 1 end   -- 交点在右侧才计数
        end
    end
    return count % 2 == 1
end
sendmsg(actor, 1, "点在多边形内：" ..
    tostring(inside(3, 3, {{1, 1}, {5, 1}, {5, 5}, {1, 5}})))