--- layout: example.html title: Layer Spy shortdesc: View a portion of one layer over another docs: >

Layer rendering can be manipulated in `prerender` and `postrender` event listeners. These listeners get an event with a reference to the Canvas rendering context. In this example, the `prerender` 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.

tags: "spy, image manipulation, maptiler" cloak: - key: get_your_own_D6rA4zTHduk6KOKTXzGB value: Get your own API key at https://www.maptiler.com/cloud/ ---