How to create a smooth scrolling for many objects?

I'm afraid that's what you'd expect - there's not enough memory to store a potentially huge offscreen image, so once you scroll off the screen, it's gone.

I guess there are two options:

• Scroll on drag, and redraw when the finger is lifted (that's what we do with OpenStreetMap and it seems like a good compromise)
  
• Allocate a large offscreen buffer (with Graphics.createArrayBuffer) or maybe store it on the SD card, and then render that image to the screen - this could still be pretty slow though.