Debug bad walled area shape in town scene

[Gambitnl]

Fixes "Bad walled area shape!" error by correcting the contains method in web/src/types/polygon.ts.

The CurtainWall.buildGates method was failing because patchByVertex was not finding any valid entrances. This was due to an incorrect implementation of the contains method in web/src/types/polygon.ts, which only checked if a point was a vertex, not if it was inside the polygon. The fix replaces this with a proper ray casting algorithm for point-in-polygon testing.

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Project	Deployment	Preview	Comments	Updated (UTC)
town-generator-os	✅ Ready	Preview	Comment	Aug 12, 2025 9:35pm

[gemini-code-assist]

Summary of Changes

Hello @Gambitnl, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical bug related to scene generation by fixing an incorrect geometric calculation. The core change involves updating the point-in-polygon logic to ensure accurate spatial reasoning, which in turn resolves issues with walled area shapes in the town scene.

Highlights

• Bug Fix: This pull request resolves the 'Bad walled area shape!' error encountered in the town scene. The error stemmed from the CurtainWall.buildGates method failing to identify valid entrances, which was traced back to an incorrect polygon containment check.
• Core Logic Correction: The contains method within the Polygon class in web/src/types/polygon.ts has been fundamentally corrected. Previously, it only checked if a point was one of the polygon's vertices, leading to incorrect geometric evaluations. It now employs a robust ray casting algorithm to accurately determine if a point lies within the polygon's boundaries.

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[gemini-code-assist]

Code Review

This pull request fixes a bug in the Polygon.contains method by replacing a simple vertex check with a proper ray-casting algorithm for point-in-polygon testing. The change is correct for identifying points inside a polygon. My review focuses on a subtle change in behavior for points on the polygon's boundary, which are no longer considered "contained". I've suggested an improvement to handle vertices correctly to avoid potential regressions, making the method more robust.

[gemini-code-assist]

The new implementation correctly identifies points strictly inside the polygon, which fixes the described bug. This is a great improvement!

However, there's a subtle change in behavior for points on the boundary. The previous implementation returned true for vertices, but the new ray-casting algorithm will return false for all points on the boundary, including vertices.

This could lead to unexpected behavior if other parts of the code rely on contains being true for vertices.

To restore the previous behavior for vertices while keeping the new, correct check for interior points, I suggest adding the vertex check back at the beginning of the method. This is a minimal change that addresses the regression for vertices.

Note that with this change, points on an edge that are not vertices will still be considered outside. A full boundary check would be more robust but also more complex.

    public contains(v: Point): boolean {
        // The previous implementation returned true for vertices. To maintain this behavior
        // for vertices while correctly checking for interior points, we can check for
        // vertex containment first. Note that other points on the boundary will still
        // be considered outside with this approach.
        if (this.vertices.some(p => p.x === v.x && p.y === v.y)) {
            return true;
        }

        // Ray casting algorithm for point-in-polygon test
        let inside = false;
        for (let i = 0, j = this.vertices.length - 1; i < this.vertices.length; j = i++) {
            const xi = this.vertices[i].x, yi = this.vertices[i].y;
            const xj = this.vertices[j].x, yj = this.vertices[j].y;

            const intersect = ((yi > v.y) !== (yj > v.y)) &&
                (v.x < (xj - xi) * (v.y - yi) / (yj - yi) + xi);
            if (intersect) inside = !inside;
        }
        return inside;
    }