Example - webgl_shadow_contact artifacts

[Fluqz]

Describe the bug

The contact shadow example from @marcofugaro, when viewed from further away or with increased plane size, starts to flimmer and get distorted shadows.

To Reproduce

Basicly just dolly out far enough in the example.
I made a live example which shows it better.

https://jsfiddle.net/h0jmwvpd/2/

Expected behavior

The shadows should stay static. No artifacts, no flimmering.

Platform:

• Device: Desktop
• OS: Windows, MacOS
• Browser: Chrome
• Three.js version: r123

[gkjohnson]

It looks like a depth precision issue because two planes are added on top of eachother with a small offset:

three.js/examples/webgl_shadow_contact.html

Line 138 in 9694de0

fillPlane.position.y -= 0.00001;

I think using polygonOffset should fix this.

[Fluqz]

Yep, that worked! Thanks
I can make a PR to update the example if you want

[gkjohnson]

@Fluqz That would be great!