private void Build()
{
var triangles = _bvhData.scene.triangles;
var vetices = _bvhData.scene.vertices;
var rootSpec = NodeSpec.New();
rootSpec.numRef = triangles.Count;
// 遍历所有图元（引用），计算根节点的包围盒
for (int i = 0; i < rootSpec.numRef; i++)
{
var pRef = PrimitiveRef.New();
pRef.triangleIdx = i;
// 计算单个图元的包围盒
for (int j = 0; j < 3; j++)
{
pRef.bounds.Union(vetices[triangles[i][j]]);
}
rootSpec.bounds.Union(pRef.bounds);
_refStack.Add(pRef);
}
// 最小重叠面积，只有重叠面积大于这个值时才考虑进行spatial split
_minOverlap = rootSpec.bounds.Area * SPLIT_ALPHA;
// 递归创建BVH
_bvhData.root = BuildNodeRecursively(rootSpec, 0);
Debug.Log("Build Completely.");
}
private void SplitReference(out PrimitiveRef leftRef, out PrimitiveRef rightRef, PrimitiveRef curRef, int dim, float pos)
{
leftRef = rightRef = PrimitiveRef.New();
leftRef.triangleIdx = rightRef.triangleIdx = curRef.triangleIdx;
var triangle = _bvhData.scene.triangles[curRef.triangleIdx];
var vertices = _bvhData.scene.vertices;
// 遍历三角形的三条边01,12,20,然后将顶点与分割平面组成包围盒
for (byte i = 0; i < 3; i++)
{
var v0 = vertices[triangle[i]];
var v1 = vertices[triangle[i + 1 == 3 ? 0 : i + 1]];
float v0p = v0[dim];
float v1p = v1[dim];
if (v0p <= pos)
{
leftRef.bounds.Union(v0);
}
if (v0p >= pos)
{
rightRef.bounds.Union(v0);
}
// 求得分割平面与三角形的交点，且算进左右两边的包围盒
if ((v0p < pos && v1p > pos) || (v0p > pos && v1p < pos))
{
Vector3 t = Vector3.Lerp(v0, v1, Mathf.Clamp((pos - v0p) / (v1p - v0p), 0.0f, 1.0f));
leftRef.bounds.Union(t);
rightRef.bounds.Union(t);
}
}
leftRef.bounds.max[dim] = pos;
rightRef.bounds.min[dim] = pos;
// 上面得到的是图元（三角形）被分割后左右两边的包围盒，但我们希望得到的包围盒除此之外，还应该限制在分割平面左右两个bin中
leftRef.bounds.Intersect(curRef.bounds);
rightRef.bounds.Intersect(curRef.bounds);
}