Merge pull request #786 from zeux/nanite-errpx

demo: Improve boundsError to take camera parameters into account

demo/main.cpp

@@ -197,7 +197,7 @@ void dumpObj(const std::vector<Vertex>& vertices, const std::vector<unsigned int
  {
  unsigned int a = indices[i], b = indices[i + 1], c = indices[i + 2];
 
- fprintf(stderr, "f %d %d %d\n", a + 1, b + 1, c + 1);
+ fprintf(stderr, "f %d//%d %d//%d %d//%d\n", a + 1, a + 1, b + 1, b + 1, c + 1, c + 1);
  }
 }
 
@@ -209,7 +209,7 @@ void dumpObj(const char* section, const std::vector<unsigned int>& indices)
  {
  unsigned int a = indices[j], b = indices[j + 1], c = indices[j + 2];
 
- fprintf(stderr, "f %d %d %d\n", a + 1, b + 1, c + 1);
+ fprintf(stderr, "f %d//%d %d//%d %d//%d\n", a + 1, a + 1, b + 1, b + 1, c + 1, c + 1);
  }
 }
 

demo/nanite.cpp

@@ -53,6 +53,7 @@ struct Cluster
 const size_t kClusterSize = 128;
 const size_t kGroupSize = 8;
 const bool kUseLocks = true;
+const bool kUseNormals = true;
 
 static LODBounds bounds(const std::vector<Vertex>& vertices, const std::vector<unsigned int>& indices, float error)
 {
@@ -107,11 +108,15 @@ static LODBounds boundsMerge(const std::vector<Cluster>& clusters, const std::ve
  return result;
 }
 
-static float boundsError(const LODBounds& bounds, float x, float y, float z)
+// computes approximate (perspective) projection error of a cluster in screen space (0..1; multiply by screen height to get pixels)
+// camera_proj is projection[1][1], or cot(fovy/2); camera_znear is *positive* near plane distance
+// for DAG cut to be valid, boundsError must be monotonic: it must return a larger error for parent cluster
+// for simplicity, we ignore perspective distortion and use rotationally invariant projection size estimation
+static float boundsError(const LODBounds& bounds, float camera_x, float camera_y, float camera_z, float camera_proj, float camera_znear)
 {
- float dx = bounds.center[0] - x, dy = bounds.center[1] - y, dz = bounds.center[2] - z;
+ float dx = bounds.center[0] - camera_x, dy = bounds.center[1] - camera_y, dz = bounds.center[2] - camera_z;
  float d = sqrtf(dx * dx + dy * dy + dz * dz) - bounds.radius;
- return d <= 0 ? FLT_MAX : bounds.error / d;
+ return bounds.error / (d > camera_znear ? d : camera_znear) * (camera_proj * 0.5f);
 }
 
 #ifdef METIS
@@ -426,7 +431,10 @@ static std::vector<unsigned int> simplify(const std::vector<Vertex>& vertices, c
 
  std::vector<unsigned int> lod(indices.size());
  unsigned int options = meshopt_SimplifySparse | meshopt_SimplifyErrorAbsolute;
- if (locks)
+ float normal_weights[3] = {0.5f, 0.5f, 0.5f};
+ if (kUseNormals)
+ lod.resize(meshopt_simplifyWithAttributes(&lod[0], &indices[0], indices.size(), &vertices[0].px, vertices.size(), sizeof(Vertex), &vertices[0].nx, sizeof(Vertex), normal_weights, 3, locks ? &(*locks)[0] : NULL, target_count, FLT_MAX, options, error));
+ else if (locks)
  lod.resize(meshopt_simplifyWithAttributes(&lod[0], &indices[0], indices.size(), &vertices[0].px, vertices.size(), sizeof(Vertex), NULL, 0, NULL, 0, &(*locks)[0], target_count, FLT_MAX, options, error));
  else
  lod.resize(meshopt_simplify(&lod[0], &indices[0], indices.size(), &vertices[0].px, vertices.size(), sizeof(Vertex), target_count, FLT_MAX, options | meshopt_SimplifyLockBorder, error));
@@ -607,20 +615,24 @@ void nanite(const std::vector<Vertex>& vertices, const std::vector<unsigned int>
  maxy = std::max(maxy, vertices[i].py * 2);
  maxz = std::max(maxz, vertices[i].pz * 2);
  }
- float threshold = 3e-3f;
+
+ float threshold = 2e-3f; // 2 pixels at 1080p
+ float fovy = 60.f;
+ float znear = 1e-2f;
+ float proj = 1.f / tanf(fovy * 3.1415926f / 180.f * 0.5f);
 
  std::vector<unsigned int> cut;
  for (size_t i = 0; i < clusters.size(); ++i)
- if (boundsError(clusters[i].self, maxx, maxy, maxz) <= threshold && boundsError(clusters[i].parent, maxx, maxy, maxz) > threshold)
+ if (boundsError(clusters[i].self, maxx, maxy, maxz, proj, znear) <= threshold && boundsError(clusters[i].parent, maxx, maxy, maxz, proj, znear) > threshold)
  cut.insert(cut.end(), clusters[i].indices.begin(), clusters[i].indices.end());
 
 #ifndef NDEBUG
  for (size_t i = 0; i < dag_debug.size(); ++i)
  {
  int j = dag_debug[i].first, k = dag_debug[i].second;
- float ej = boundsError(clusters[j].self, maxx, maxy, maxz);
- float ejp = boundsError(clusters[j].parent, maxx, maxy, maxz);
- float ek = boundsError(clusters[k].self, maxx, maxy, maxz);
+ float ej = boundsError(clusters[j].self, maxx, maxy, maxz, proj, znear);
+ float ejp = boundsError(clusters[j].parent, maxx, maxy, maxz, proj, znear);
+ float ek = boundsError(clusters[k].self, maxx, maxy, maxz, proj, znear);
 
  assert(ej <= ek);
  assert(ejp >= ej);
@@ -634,7 +646,7 @@ void nanite(const std::vector<Vertex>& vertices, const std::vector<unsigned int>
  dumpObj(vertices, cut);
 
  for (size_t i = 0; i < clusters.size(); ++i)
- if (boundsError(clusters[i].self, maxx, maxy, maxz) <= threshold && boundsError(clusters[i].parent, maxx, maxy, maxz) > threshold)
+ if (boundsError(clusters[i].self, maxx, maxy, maxz, proj, znear) <= threshold && boundsError(clusters[i].parent, maxx, maxy, maxz, proj, znear) > threshold)
  dumpObj("cluster", clusters[i].indices);
  }
 }