Drawing no intersected polygon with dragging vertexes

Question

I'm trying to draw a polygon without intersecting.

Below is good example which I want to.

Bad example what I want to prevent.

If I choose red dot one, then what algorithm I can apply to prevent the intersecting sides of the polygon?

Answer 1

Technical answer:

The moving point must belong to the visibility zones of its two neighbors (ignoring the two adjoining edges).

You can construct these two zones and their intersection once for all, then constrain the cursor to remain in the intersection. This can be made efficiently in time O(Log(N)) per query, after some preprocessing. But this is quite complex and not worth the effort.

Practical answer:

Simply check that the two edges from the moving point do not intersect the remaining edges.