ScratchCanvas.prototype.measureStringWidth = function(font, str) {
if (util.none(str)) {
str = "M";
}
var context = this.getContext();
context.save();
context.font = font;
var width = context.measureText(str).width;
context.restore();
return width;
};
var ScratchCanvas = function() {
this._canvas = document.getElementById('skywriter-scratch-canvas');
// It's possible that another ScratchCanvas instance in another sandbox
// exists on the page. If so, we assume they're compatible, and use
// that one.
if (util.none(this._canvas)) {
this._canvas = document.createElement('canvas');
this._canvas.id = 'skywriter-scratch-canvas';
this._canvas.width = 400;
this._canvas.height = 300;
this._canvas.style.position = 'absolute';
this._canvas.style.top = "-10000px";
this._canvas.style.left = "-10000px";
document.body.appendChild(this._canvas);
}
};