Only the specified area is reserved

Questions
1

I now want to achieve something similar to the image below, but I only want to keep the inside of the area instead of outside of the area

image
image766×468 62.6 KB

Since the area requiring mask is irregular and may be a very complex polygon, such as the border of a province or city, I want to use stencil buffer to achieve the above functions, but I feel a little confused. Does anyone have similar implementation ideas, thank you in advance.

2

One possible way is to define the boundary as a shape and then extrude it with THREE.ExtrudeGeometry. I used this approach in a small library for making maps.

https://boytchev.github.io/map/

Example:

image

3

Thank you, but things are a little different, I need like this. https://forum.unity.com/threads/cull-rendering-between-camera-and-stencil-mask.544280/

4

Would CSG (Constructive solid geometry) help?

5

Is there any code example for this

6
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