geom/m44753: guard adjacent child contextualization with a GPS flag

The commit adds a flag to conditionally enable/disable the feature.

doc/README.options.md

@@ -172,6 +172,10 @@ respectively.
 Controls the use of early termination of the geometry octree for
 isolated points.
 
+### `--adjacentChildContextualization=0|1`
+Controls the contextualization of occupancy bits according to the
+state of adjacent children of neighbouring nodes.
+
 ### `--intra_pred_max_node_size_log2=INT-VALUE`
 Intra occupancy prediction uses an octree node's neighbours to predict
 its occupancy.  The prediction mode is enabled for octree nodes smaller

tmc3/OctreeNeighMap.cpp

@@ -134,6 +134,7 @@ updatePatternFromNeighOccupancy(
 
 GeometryNeighPattern
 makeGeometryNeighPattern(
+  bool adjacent_child_contextualization_enabled_flag,
   const PCCVector3<uint32_t>& position,
   const int nodeSizeLog2,
   const MortonMap3D& occupancyAtlas)
@@ -171,6 +172,9 @@ makeGeometryNeighPattern(
   // the occupancy contextualisation bits.
   GeometryNeighPattern gnp = {neighPattern, 0, 0};
 
+  if (!adjacent_child_contextualization_enabled_flag)
+    return gnp;
+
   if (x > 0)
     gnp = updatePatternFromNeighOccupancy(occupancyAtlas, x - 1, y, z, gnp, 0);
 

tmc3/OctreeNeighMap.h

@@ -166,10 +166,12 @@ struct GeometryNeighPattern {
 };
 
 //============================================================================
-
 // determine the occupancy pattern of the six neighbours of the node at
-// @position.
+// @position.  If @adjacent_child_contextualization_enabled_flag is true,
+// the occupancy state of previously coded neighbours is used to refine
+// the neighbour pattern and derive external adjacency counts for each child.
 GeometryNeighPattern makeGeometryNeighPattern(
+  bool adjacent_child_contextualization_enabled_flag,
   const PCCVector3<uint32_t>& currentPosition,
   const int nodeSizeLog2,
   const MortonMap3D& occupancyAtlas);

tmc3/TMC3.cpp

@@ -363,6 +363,10 @@ ParseParameters(int argc, char* argv[], Parameters& params)
     params.encoder.gps.inferred_direct_coding_mode_enabled_flag, true,
     "Permits early termination of the geometry octree for isolated points")
 
+  ("adjacentChildContextualization",
+    params.encoder.gps.adjacent_child_contextualization_enabled_flag, true,
+    "Occupancy contextualization using neighbouring adjacent children")
+
   ("intra_pred_max_node_size_log2",
     params.encoder.gps.intra_pred_max_node_size_log2, 0,
     "octree nodesizes eligible for occupancy intra prediction")

tmc3/geometry_octree_decoder.cpp

@@ -451,8 +451,10 @@ decodeGeometryOctree(
         node0.pos, nodeSizeLog2, fifo, fifoCurrLvlEnd, &occupancyAtlas,
         &occupancyAtlasOrigin);
 
-      GeometryNeighPattern gnp =
-        makeGeometryNeighPattern(node0.pos, nodeSizeLog2, occupancyAtlas);
+      GeometryNeighPattern gnp = makeGeometryNeighPattern(
+        gps.adjacent_child_contextualization_enabled_flag, node0.pos,
+        nodeSizeLog2, occupancyAtlas);
+
       node0.neighPattern = gnp.neighPattern;
       occupancyAdjacencyGt0 = gnp.adjacencyGt0;
       occupancyAdjacencyGt1 = gnp.adjacencyGt1;

tmc3/geometry_octree_encoder.cpp

@@ -479,8 +479,10 @@ encodeGeometryOctree(
         node0.pos, nodeSizeLog2, fifo, fifoCurrLvlEnd, &occupancyAtlas,
         &occupancyAtlasOrigin);
 
-      GeometryNeighPattern gnp =
-        makeGeometryNeighPattern(node0.pos, nodeSizeLog2, occupancyAtlas);
+      GeometryNeighPattern gnp = makeGeometryNeighPattern(
+        gps.adjacent_child_contextualization_enabled_flag, node0.pos,
+        nodeSizeLog2, occupancyAtlas);
+
       node0.neighPattern = gnp.neighPattern;
       occupancyAdjacencyGt0 = gnp.adjacencyGt0;
       occupancyAdjacencyGt1 = gnp.adjacencyGt1;

tmc3/hls.h

@@ -190,6 +190,11 @@ struct GeometryParameterSet {
   // Selects between bitwise and bytewise occupancy coding
   bool bitwise_occupancy_coding_flag;
 
+  // Controlls contextualization of occupancy bits and refinement of
+  // the neighbour pattern according to the occupancy of adjacent
+  // children in neighbouring nodes.
+  bool adjacent_child_contextualization_enabled_flag;
+
   // Experimental knob to control the number of contexts used
   // for occupancy coding.
   int geom_occupancy_ctx_reduction_factor;

tmc3/io_hls.cpp

@@ -194,6 +194,7 @@ write(const GeometryParameterSet& gps)
   bs.write(gps.neighbour_context_restriction_flag);
   bs.write(gps.inferred_direct_coding_mode_enabled_flag);
   bs.write(gps.bitwise_occupancy_coding_flag);
+  bs.write(gps.adjacent_child_contextualization_enabled_flag);
   bs.writeUe(gps.geom_occupancy_ctx_reduction_factor);
   bs.writeUe(gps.neighbour_avail_boundary_log2);
   bs.writeUe(gps.intra_pred_max_node_size_log2);
@@ -222,6 +223,7 @@ parseGps(const PayloadBuffer& buf)
   bs.read(&gps.neighbour_context_restriction_flag);
   bs.read(&gps.inferred_direct_coding_mode_enabled_flag);
   bs.read(&gps.bitwise_occupancy_coding_flag);
+  bs.read(&gps.adjacent_child_contextualization_enabled_flag);
   bs.readUe(&gps.geom_occupancy_ctx_reduction_factor);
   bs.readUe(&gps.neighbour_avail_boundary_log2);
   bs.readUe(&gps.intra_pred_max_node_size_log2);