图像在 Lua LÖVE 游戏中无法移动

我正在用 Lua LÖVE 框架编写 LudumDare26 游戏。当我按下 WASD 键时，玩家角色看起来无法移动。

function love.draw()

    playerX = 10
    playerY = 10

    if love.keyboard.isDown ("w") then
        playerY = playerY - 1
    elseif love.keyboard.isDown ("s") then
        playerY = playerY + 1
    elseif love.keyboard.isDown ("a") then
        playerX = playerX - 1
    elseif love.keyboard.isDown ("d") then
        playerX = playerX + 1
    end

    local x = love.mouse.getX()
    local y = love.mouse.getY()

    love.graphics.setColor(0, 200, 255, 100)
    love.graphics.rectangle("fill", 0, 0, 800, 300)

    love.graphics.setColor(255, 255, 255, 255)
    love.graphics.rectangle("fill", xCloud, 128, 128, 50)

    love.graphics.setColor(50, 160, 80, 255)
    love.graphics.rectangle("fill", 0, 300, 800, 300)

    love.graphics.setColor(255, 0, 0, 255)
    love.graphics.draw(corsair, x - 16, y - 16, 0, 1, 1, 0, 0)

    love.graphics.draw(player, playerX, playerY)

    love.graphics.line(playerX, playerY, x, y)
end