Unity中如何让子物体在父物体的Polygon Collider 2D范围内正确随机生成位置？

Hey there! I totally get the frustration—your current code uses the axis-aligned bounding box (AABB) of the Polygon Collider 2D (via bounds), which is just a square that wraps around your polygon. That’s why ~20% of the time your circle ends up outside the collider: you’re picking random points in that square, not just the area inside the actual polygon shape.

Here are two solid solutions to fix this:

Solution 1: Simple Rejection Sampling (Easy to Implement) #

This method picks a random point in the bounding box, checks if it’s inside the polygon, and repeats until it finds a valid point. It’s straightforward and works great for most use cases.

First, fix two key issues in your original code:

• bounds.min/max are world space coordinates, but you’re assigning them directly to localPosition (which is relative to the parent). This can cause offset issues if your parent has any position/scale/rotation.
• You need to verify the point is actually inside the polygon collider.

Here’s the updated code:

private PolygonCollider2D polygonCollider;
private Bounds bounds;

private void GetBounds() {
    polygonCollider = transform.parent.GetComponent<PolygonCollider2D>();
    bounds = polygonCollider.bounds;
}

public void TargetSetPosition() {
    Vector2 worldPoint;
    int maxAttempts = 100;
    int attempts = 0;

    do {
        // Generate a random point within the collider's world space bounds
        float x = Random.Range(bounds.min.x, bounds.max.x);
        float y = Random.Range(bounds.min.y, bounds.max.y);
        worldPoint = new Vector2(x, y);
        
        attempts++;
        // Prevent infinite loops in edge cases (e.g., super narrow polygons)
        if (attempts > maxAttempts) {
            Debug.LogWarning("Couldn't find a valid point inside the polygon after 100 attempts");
            break;
        }
    } while (!polygonCollider.OverlapPoint(worldPoint));

    // Convert the valid world point to local space for the child object
    transform.localPosition = polygonCollider.transform.InverseTransformPoint(worldPoint);
}

private void Start() {
    GetBounds();
    TargetSetPosition();
}

Key Fixes Explained: #

• polygonCollider.OverlapPoint(worldPoint) checks if the generated point is inside the polygon’s actual shape.
• InverseTransformPoint converts the world space point to the parent’s local space, so your circle positions correctly relative to the parent.
• The attempt limit prevents infinite loops if the polygon is tiny or oddly shaped.

Solution 2: Triangulation-Based Sampling (Better Performance for Complex Polygons) #

If you’re dealing with very complex polygons and notice performance hits from rejection sampling, you can triangulate the polygon first. This splits the shape into triangles, then you randomly select a triangle and generate a point inside it.

This requires a bit more code, but here’s a quick outline:

1. Use a triangulator to split your Polygon Collider 2D’s points into triangles.
2. Assign a weight to each triangle based on its area (so larger triangles have a higher chance of being selected).
3. Generate a random point inside the selected triangle using barycentric coordinates.

For most projects, Solution 1 will be more than sufficient, but this is a good option if you need maximum efficiency.

内容的提问来源于stack exchange，提问作者ludvik120