View a portion of one layer over another
Layer rendering can be manipulated in precompose
and postcompose
event listeners. These listeners get an event with a reference to the Canvas rendering context. In this example, the precompose
listener sets a clipping mask around the most recent mouse position, giving you a spyglass effect for viewing one layer over another.
Move around the map to see the effect. Use the ↑ up and ↓ down arrow keys to adjust the spyglass size.