Is it possible storing drawn graphics into temp bitmap for later alpha composition on HTML5 canvas?

I'm making some kind of UI layers with HTML5 canvas. All layers can开发者_C百科 be nested and can have alpha. Nested layers should be drawn with correct alpha composition. To do this, some kind of temporary bitmap storage is required. How can I store graphics drawing into temp bitmap?

---

You can always make a canvas in memory (as in not add it to the DOM)

storedCanvas = document.createElement('canvas');

Then you can paint an entire canvas to that canvas:

storedCtx.drawImage(firstCanvas, 0, 0);

Then you can do whatever you want to the first canvas, the stored one won't change. Then, when you want to recall that, you just do

firstCanvasCtx.drawImage(storedCanvas, 0, 0);