canvas的globalCompositeOperation真机无效
设置 canvas.globalCompositeOperation=“destination-out”,真机模拟器都正常
设置 canvas.globalCompositeOperation=“destination-in”,模拟器都正常,真机无效
设置 canvas.globalCompositeOperation=“destination-out”,真机模拟器都正常
设置 canvas.globalCompositeOperation=“destination-in”,模拟器都正常,真机无效