脚本中的函数定义必须出现在文件的结尾。 请将 "update_velocity" 函数定义后面的所有语句都移到第一个局部函数定义前面。

好的，可以将 "update_velocity" 函数定义后面的所有语句移到第一个局部函数定义前面，如下所示：

local function update_velocity()
    -- 更新小球速度
    ball.vx = ball.vx + ball.ax
    ball.vy = ball.vy + ball.ay

    -- 限制小球速度
    if ball.vx > ball.max_vx then
        ball.vx = ball.max_vx
    elseif ball.vx < -ball.max_vx then
        ball.vx = -ball.max_vx
    end

    if ball.vy > ball.max_vy then
        ball.vy = ball.max_vy
    elseif ball.vy < -ball.max_vy then
        ball.vy = -ball.max_vy
    end

    -- 小球碰到边界反弹
    if ball.x < ball.radius then
        ball.x = ball.radius
        ball.vx = -ball.vx * ball.restitution
        audio.play_sound("bounce")
    elseif ball.x > SCREEN_WIDTH - ball.radius then
        ball.x = SCREEN_WIDTH - ball.radius
        ball.vx = -ball.vx * ball.restitution
        audio.play_sound("bounce")
    end

    if ball.y < ball.radius then
        ball.y = ball.radius
        ball.vy = -ball.vy * ball.restitution
        audio.play_sound("bounce")
    elseif ball.y > SCREEN_HEIGHT - ball.radius then
        ball.y = SCREEN_HEIGHT - ball.radius
        ball.vy = -ball.vy * ball.restitution
        audio.play_sound("bounce")
    end
end

-- 程序入口
function love.load()
    -- 初始化随机数生成器
    math.randomseed(os.time())

    -- 加载音效
    audio.load_sounds()

    -- 加载字体
    font = love.graphics.newFont("fonts/font.ttf", 24)

    -- 设置窗口模式
    love.window.setMode(SCREEN_WIDTH, SCREEN_HEIGHT, {
        fullscreen = false,
        resizable = false,
        vsync = true
    })

    -- 设置窗口标题
    love.window.setTitle("Ball Game")

    -- 创建小球
    create_ball()

    -- 初始化游戏状态
    game_state = "start"
end

function love.update(dt)
    if game_state == "play" then
        -- 更新小球位置
        ball.x = ball.x + ball.vx * dt
        ball.y = ball.y + ball.vy * dt

        -- 更新小球速度
        update_velocity()

        -- 更新计时器
        timer = timer + dt

        -- 判断游戏是否结束
        if timer >= GAME_DURATION then
            game_state = "over"
            audio.play_sound("gameover")
        end
    end
end

function love.draw()
    -- 绘制背景
    love.graphics.setColor(1, 1, 1)
    love.graphics.draw(background, 0, 0)

    -- 绘制小球
    love.graphics.setColor(ball.color)
    love.graphics.circle("fill", ball.x, ball.y, ball.radius)

    -- 绘制分数
    love.graphics.setFont(font)
    love.graphics.setColor(0, 0, 0)
    love.graphics.print("Score: " .. score, 10, 10)

    -- 绘制时间
    local time_left = math.ceil(math.max(0, GAME_DURATION - timer))
    love.graphics.print("Time: " .. time_left, SCREEN_WIDTH - 100, 10)

    -- 绘制游戏结束画面
    if game_state == "over" then
        love.graphics.setColor(0, 0, 0, 0.5)
        love.graphics.rectangle("fill", 0, 0, SCREEN_WIDTH, SCREEN_HEIGHT)
        love.graphics.setColor(1, 1, 1)
        love.graphics.printf("Game Over!", font, 0, SCREEN_HEIGHT / 2 - 50, SCREEN_WIDTH, "center")
        love.graphics.printf("Final Score: " .. score, font, 0, SCREEN_HEIGHT / 2, SCREEN_WIDTH, "center")
        love.graphics.printf("Press Enter to Restart", font, 0, SCREEN_HEIGHT / 2 + 50, SCREEN_WIDTH, "center")
    end
end

function love.keypressed(key)
    if key == "escape" then
        love.event.quit()
    elseif key == "return" then
        if game_state == "start" or game_state == "over" then
            -- 重置游戏状态
            score = 0
            timer = 0
            create_ball()
            game_state = "play"
        end
    end
end