slices/m49121: constrain slice partitions to trisoup node size

This avoids artefacts during trisoup generation by checking whether the
original slice partition interval is an integer multiple of the block
size W=2^(trisoup_node_size_log2). If not, the partition interval is
rounded up to the nearest integer that is exactly divisible by the block
size.

tmc3/encoder.cpp

@@ -182,7 +182,8 @@ PCCTMC3Encoder3::compress(
       case PartitionMethod::kNone: return 1;
 
       case PartitionMethod::kUniformGeom:
-        curSlices = partitionByUniformGeom(params->partition, tileCloud, t);
+        curSlices = partitionByUniformGeom(
+          params->partition, tileCloud, t, _gps->trisoup_node_size_log2);
         break;
 
       case PartitionMethod::kOctreeUniform:

tmc3/partitioning.cpp

@@ -101,7 +101,10 @@ shortestAxis(const Box3<T>& curBox)
 
 std::vector<Partition>
 partitionByUniformGeom(
-  const PartitionParams& params, const PCCPointSet3& cloud, int tileID)
+  const PartitionParams& params,
+  const PCCPointSet3& cloud,
+  int tileID,
+  int partitionBoundaryLog2)
 {
   std::vector<Partition> slices;
 
@@ -116,6 +119,13 @@ partitionByUniformGeom(
   int sliceNum = minEdge ? (maxEdge / minEdge) : 1;
   int sliceSize = minEdge ? minEdge : maxEdge;
 
+  // In order to avoid issues with trisoup, don't partition points within
+  // a trisoup node, otherwise there will be issues fitting triangles.
+  int partitionBoundary = 1 << partitionBoundaryLog2;
+  if (sliceSize % partitionBoundary) {
+    sliceSize = (1 + sliceSize / partitionBoundary) * partitionBoundary;
+  }
+
   while (1) {
     slices.clear();
     slices.resize(sliceNum);

tmc3/partitioning.h

@@ -106,7 +106,10 @@ struct PartitionSet {
 //============================================================================
 
 std::vector<Partition> partitionByUniformGeom(
-  const PartitionParams& params, const PCCPointSet3& cloud, int tileID);
+  const PartitionParams& params,
+  const PCCPointSet3& cloud,
+  int tileID,
+  int paritionBoundaryLog2);
 
 std::vector<Partition> partitionByOctreeDepth(
   const PartitionParams& params,