通过 window.innerWidth 和css填充canvas满屏的方法

gistfile1.js

        function adjust(canvas, rw, rh) {
            var width = window.innerWidth;
            //var ratio = rw / rh; //canvas.width / canvas.height;
            //var height = width / ratio;
            if(!rw){
                rw = canvas.width
                rh = canvas.height
            }
            var height = width * rh / rw ;

            canvas.style.width = width + 'px';
            canvas.style.height = height + 'px';
        }
        adjust(canvas, 4, 3);