ClockwiseSweepPolygon can be self-intersecting

[dev7355608]

Related Issues

• Improve the computation of polygons which include threshold wall attenuation regions. #9531

The rounding of internal edge collision points in ClockwiseSweep._getInternalEdgeCollision can produce self-intersections, which can break the triangulation and Weiler-Atherton clipping.

fvtt-Scene-clockwisesweeppolygon-bug-ILliaF3KAqYFKdBh.zip

Related Issue

CONFIG.Canvas.polygonBackends.sight.create({x: 3516, y: 4277}, { type: "sight" }).visualize()

fvtt-Scene-clockwisesweeppolygon-bug-AVISfGBXmLexULqs.zip

[aaclayton]

Going to have to defer this to V13. We are running out of time before stable and this should ideally be done earlier in a cycle so we have ample time to test it.

[dev7355608]

Originally reported by zemoloch: https://discord.com/channels/170995199584108546/1184176415139184731/1255152698903494780

ALL MODULES DISABLED? true
OS, Hosting, Browser (if applicable): V12.237
Short Description of bug: Terrain walls cause seemingly random spots near the Terrain Walls to break. The vision of a token that enters this spot penetrates all walls for a brief moment, causing a flicker and revealing the entire map within the token vision range, even through walls. The problem does not occur when terrain walls are removed.
Simple steps to reproduce the bug: Place Terrain Walls surrounded by Basic Walls.
Screenshots and/or console errors:
Screenshot 1: Token vision ends at walls as expected.
Screenshot 2: The token moves to the left and the vision flickers through all walls. It reveals the entire Fog of War within vision range, even across walls and rooms, in a circle.
Screenshot 3: Walls.
Scene json includes token on the right of a problematic spot.

fvtt-Scene-crypt-Rcsln2t4KKOw6tgh.json

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Additional comment by crovaxon: https://discord.com/channels/170995199584108546/1184176415139184731/1255161672331690059

Addendum to this bug report since I was interacting with Moloch and managed to confirm it.
I suggest setting a white background color on the scene config shared by Moloch to make the fog of war and vision of that token easy to see (and funnily enough will turn the white mystery man SVG invisible :P).

I created a vid demonstrating the flicker and I can identify one key terrain wall group that while it is there, will almost always trigger that flicker. But even removing the marked terrain walls will still very rarely produce a flicker if I keep spamming left and right fairly quickly on that token in the position that Moloch has in the screenshots, likely an interaction with other terrain walls.

Another discovery: this happens while the token has a vision of 60 ft set. If you remove that vision and instead give it a light source of 60 ft, this flicker does not occur.

2024-06-25_15-35-55.webm