Lua点到线段：投影夹取的距离计算

local function dist(px, py, x1, y1, x2, y2)
    local dx, dy = x2 - x1, y2 - y1
    local t = ((px-x1)*dx + (py-y1)*dy) / (dx*dx + dy*dy)
    local qx, qy = x1 + t * dx, y1 + t * dy   -- 未夹取，垂足越界
    return math.sqrt((px-qx)^2 + (py-qy)^2)
end

local function dist(px, py, x1, y1, x2, y2)
    local dx, dy = x2 - x1, y2 - y1
    local len2 = dx * dx + dy * dy
    local t = len2 == 0 and 0
        or math.max(0, math.min(1,
            ((px-x1)*dx + (py-y1)*dy) / len2))
    local qx, qy = x1 + t * dx, y1 + t * dy
    return math.sqrt((px-qx)^2 + (py-qy)^2)
end
sendmsg(actor, 1, "点到线段最短距离 "
    .. string.format("%.2f", dist(5, 5, 0, 0, 4, 0)))