将canvas高宽调整为100%

<style>
body {
	padding:0px;
	margin:0px;
        width: 100%;
        height: 100%;
}

    #cvs {
        position:fixed;
	width:100%;
	height:100%
    }
</style>

注意是#cvs而不是canvas，因为会和二维码qrcode冲突

<canvas id="cvs"></canvas>

function resize_canvas(){
            canvas = document.getElementById("canvas");
            if (canvas.width  < window.innerWidth)
            {
                canvas.width  = window.innerWidth;
            }
 
            if (canvas.height < window.innerHeight)
            {
                canvas.height = window.innerHeight;
            }
      }