Unity实现喷漆效果

public GameObject[] GetAffectedObjects(Bounds bounds, LayerMask affectedLayers)
{
 MeshRenderer[] renderers = FindObjectsOfType<MeshRenderer>();
 List<GameObject> objects = new List<GameObject>();
 foreach (Renderer r in renderers)
 {
 if (!r.enabled) continue;
 if ((1 << r.gameObject.layer & affectedLayers.value) == 0) continue;
 if (r.GetComponent<Decal>() != null) continue;

 if (bounds.Intersects(r.bounds))
 {
 objects.Add(r.gameObject);
 }
 }
 return objects.ToArray();
}

public void BuildDecal(GameObject affectedObject, bool isLast)
{
 Mesh affectedMesh = affectedObject.GetComponent<MeshFilter>().sharedMesh;
 if (affectedMesh == null) return;

 //这里预存了已获取物体的vertices和triangles，减少了不必要的GC
 Vector3[] vertices = GetVertexList(affectedObject);
 int[] triangles = GetTriangleList(affectedObject);

 //目标顶点转换到当前物体的模型空间
 Matrix4x4 matrix = this.transform.worldToLocalMatrix*affectedObject.transform.localToWorldMatrix;
 //将主要计算移入异步
 Loom.RunAsync(() =>
 {
 for (int i = 0; i < triangles.Length; i += 3)
 {
 int i1 = triangles[i];
 int i2 = triangles[i + 1];
 int i3 = triangles[i + 2];

 Vector3 v1 = matrix.MultiplyPoint(vertices[i1]);
 Vector3 v2 = matrix.MultiplyPoint(vertices[i2]);
 Vector3 v3 = matrix.MultiplyPoint(vertices[i3]);

 Vector3 side1 = v2 - v1;
 Vector3 side2 = v3 - v1;
 Vector3 normal = Vector3.Cross(side1, side2).normalized;

 if (Vector3.Angle(-Vector3.forward, normal) >= maxAngle) continue;

 DecalPolygon poly = new DecalPolygon(v1, v2, v3);

 //用立方体裁剪
 poly = DecalPolygon.ClipPolygon(poly, right);
 if (poly == null) continue;
 poly = DecalPolygon.ClipPolygon(poly, left);
 if (poly == null) continue;
 poly = DecalPolygon.ClipPolygon(poly, top);
 if (poly == null) continue;
 poly = DecalPolygon.ClipPolygon(poly, bottom);
 if (poly == null) continue;
 poly = DecalPolygon.ClipPolygon(poly, front);
 if (poly == null) continue;
 poly = DecalPolygon.ClipPolygon(poly, back);
 if (poly == null) continue;

 AddPolygon(poly, normal);
 }

 if (isLast)
 {
 RenderDecal();
 }
 });
}

/// <summary>
/// 两面相交裁剪
/// </summary>
public static DecalPolygon ClipPolygon(DecalPolygon polygon, Plane plane)
{
 //相交为True
 bool[] positive = new bool[9];
 int positiveCount = 0;

 for (int i = 0; i < polygon.vertices.Count; i++)
 {
 positive[i] = !plane.GetSide(polygon.vertices[i]); //不在裁剪面正面，说明有相交
 if (positive[i]) positiveCount++;
 }

 if (positiveCount == 0)
 return null; //全都在裁剪面正面面，不相交
 if (positiveCount == polygon.vertices.Count) return polygon; //全都在裁剪面反面，完全相交

 DecalPolygon tempPolygon = new DecalPolygon();

 for (int i = 0; i < polygon.vertices.Count; i++)
 {
 int next = i + 1;
 next %= polygon.vertices.Count;

 if (positive[i])
 {
 tempPolygon.vertices.Add(polygon.vertices[i]);
 }

 if (positive[i] != positive[next])
 {
 Vector3 v1 = polygon.vertices[next];
 Vector3 v2 = polygon.vertices[i];

 Vector3 v = LineCast(plane, v1, v2);
 tempPolygon.vertices.Add(v);
 }
 }

 return tempPolygon;
}

public void RenderDecal()
{
 //主线程渲染
 Loom.QueueOnMainThread(() =>
 {
 if (sprite == null || Renderer == null||filter==null)
  {
   return;
  }
  //生成uv信息
  GenerateTexCoords(0, sprite);
  //距离偏移
 Push(pushDistance);

 Mesh mesh = CreateMesh();
 if (mesh != null) {
 mesh.name = "DecalMesh";
 filter.mesh = mesh;
 Renderer.material = material;
 Renderer.enabled = true;
 }
 });
}