in web/src/drawing.js [80:95]
DrawingCell.prototype._redraw = function() {
if (this._paths.length === 0) {
this._emptyLabel.style.display = 'block';
} else {
this._emptyLabel.style.display = 'none';
}
var ctx = this._canvas.getContext('2d');
var size = this.size * UPSAMPLE;
ctx.clearRect(0, 0, size, size);
ctx.strokeStyle = '#777';
ctx.lineWidth = LINE_WIDTH * size;
ctx.lineCap = 'round';
ctx.lineJoin = 'round';
drawPaths(ctx, size, this._paths);
};