Canvas 描画内容を薄く消す - jsdo.it - Share JavaScript, HTML5 and CSS// forked from akm2's "Canvas clearArc()" http://jsdo.it/akm2/e8CK CanvasRenderingContext2D.prototype.clear = function() { this.save(); this.globalCompositeOperation = 'destination-out'; this.fillStyle = 'black'; this.fill(); this.restore(); }; CanvasRenderingContext2D.prototype.clearArc = function(x, y, radius, startAngle, endAngle, anticlockwise) { this.beginPath(); this.arc(x, y, radius, startA
