求助 GUI.Label 文字重影

function Start()
{
//初始化赋值
str = "Plead click button.";
}
function OnGUI()
{
//显示提示信息内容
GUI.Label(Rect(10, 10, Screen.width, 30), str);
if(GUI.Button(Rect(10,50,buttonTexture.width,buttonTexture.height),buttonTexture)){
//点击按钮修改提示信息
str = "You click the image.";
}
}