Unity 3D运行时如何处理自定义形状的地形区域？

Hey there, let's work through this terrain elevation problem you're facing. You've got a Line Renderer-based tool to mark closed terrain shapes, and you can lift the vertices that align with the Line Renderer's points—but the inner terrain vertices aren't being affected, even after trying polygon fill algorithms. Let's break down what might be going wrong and how to fix it.

First: Verify Your Polygon's Closure & Point Order #

Most polygon fill/inside-check failures start here. Make sure:

• Your Line Renderer is properly closed: Enable LineRenderer.loop = true so the last point connects back to the first. If you're manually adding points, double-check that the final point matches the initial one (or handle the closure in code when passing points to your algorithm).
• Your points follow a consistent winding order (clockwise or counter-clockwise). Mixed-up order can break intersection calculations. You can validate this by calculating the polygon's signed area: a positive value means counter-clockwise, negative is clockwise. If the area is near zero, your points are probably colinear or ordered incorrectly.

Implement a Reliable Point-in-Polygon Check #

The Ray Casting Algorithm is usually more robust for this use case than scanline fill, especially when dealing with individual terrain vertices. Here's a tested implementation (Unity C# example) that handles most edge cases:

bool IsVertexInsidePolygon(Vector3 worldVertex, List<Vector3> polygonWorldPoints)
{
    // Convert everything to 2D (assuming terrain is on X-Z plane; adjust if your terrain uses a different axis)
    Vector2 vertex = new Vector2(worldVertex.x, worldVertex.z);
    int intersectionCount = 0;
    int pointCount = polygonWorldPoints.Count;

    for (int i = 0; i < pointCount; i++)
    {
        Vector2 p1 = new Vector2(polygonWorldPoints[i].x, polygonWorldPoints[i].z);
        Vector2 p2 = new Vector2(polygonWorldPoints[(i + 1) % pointCount].x, polygonWorldPoints[(i + 1) % pointCount].z);

        // Skip horizontal edges to avoid false intersections with rays aligned to edges
        if (Mathf.Approximately(p1.y, p2.y))
            continue;

        // Check if the vertex's Y is within the edge's Y range
        bool isVertexBelowP1 = vertex.y < p1.y;
        bool isVertexBelowP2 = vertex.y < p2.y;
        if (isVertexBelowP1 != isVertexBelowP2)
        {
            // Calculate where the horizontal ray from the vertex intersects the edge
            float intersectX = (vertex.y - p1.y) * (p2.x - p1.x) / (p2.y - p1.y) + p1.x;
            // If the intersection is to the right of the vertex, count it
            if (vertex.x < intersectX)
                intersectionCount++;
        }
    }

    // Odd count means the vertex is inside the polygon
    return intersectionCount % 2 == 1;
}

Key notes for this code:

• Adjust the axis conversion if your terrain uses a different plane (e.g., X-Y instead of X-Z).
• The (i + 1) % pointCount handles the wrap-around to the first point for closure.
• Skipping horizontal edges avoids edge cases where the ray lies exactly on a polygon edge.

Apply the Check to Your Terrain Vertices #

Once you have the inside-check working, you need to iterate over your terrain's vertices and lift the ones that pass the test:

For Unity's Built-in Terrain #

1. Convert your Line Renderer's world points to terrain-local space using terrain.transform.InverseTransformPoint().
2. Get the terrain's heightmap data with terrain.terrainData.GetHeights().
3. Calculate the bounds of your polygon (min/max X/Z) to limit the vertices you need to check (performance optimization).
4. For each heightmap pixel (convert to world space), run the IsVertexInsidePolygon check. If true, adjust the height value.
5. Update the terrain with terrain.terrainData.SetHeights().

For Custom Mesh Terrain #

1. Iterate over each vertex in your mesh's vertices array.
2. Run the inside-check on each vertex's world position.
3. Adjust the Y (or elevation) value of vertices that are inside.
4. Mark the mesh as dirty and update it with mesh.RecalculateBounds() and meshFilter.mesh = mesh.

Optimize for Performance #

If you're working with large terrains, checking every single vertex can be slow. Try these optimizations:

• Bounding Box Culling: Calculate the axis-aligned bounding box (AABB) of your polygon first, and only check vertices that fall within this box.
• Spatial Partitioning: Split your terrain into chunks, and only process chunks that overlap with the polygon's AABB.

Debugging Tips #

• Use Gizmos to draw your polygon and the vertices you're lifting in the Scene view—this helps spot misaligned points or incorrect inside/outside calls.
• Test with simple shapes first (square, triangle) to confirm your algorithm works before moving to complex polygons.
• Print debug logs for vertices that are incorrectly classified (e.g., "Vertex X is inside? false" when it should be true) to isolate edge cases.

内容的提问来源于stack exchange，提问作者Indrek Kaine