m43662/geometry: replace neighb=0 with sibling neighbour constraint

In the contextualisation of occupancy coding using neighbour patterns,
this commit replaces the case when neighbour contextualisation is
disabled with a constraint that restricts neighbour contextualisation
only examine the direct siblings of a node.

The restriction ensures that at most three neighbours may be present
for a node.

The configuration option "neighbourContextualisation=1" is replaced with
"neighbourContextRestriction=0".

tmc3/PCCTMC3Common.h

@@ -262,9 +262,12 @@ PCCBuildPredictors(
 //---------------------------------------------------------------------------
 // Update the neighbour pattern flags for a node and the 'left' neighbour on
 // each axis.  This update should be applied to each newly inserted node.
+//
+// @param siblingRestriction limits neighbours to direct siblings of child
 
 inline void
 updateGeometryNeighState(
+  bool siblingRestriction,
   const ringbuf<PCCOctree3Node>::iterator& bufEnd,
   int64_t numNodesNextLvl,
   int childSizeLog2,
@@ -273,7 +276,10 @@ updateGeometryNeighState(
   uint8_t neighPattern,
   uint8_t parantOccupancy)
 {
-  uint64_t midx = child.mortonIdx = mortonAddr(child.pos, childSizeLog2);
+  uint64_t midx;
+  if (!siblingRestriction) {
+    midx = child.mortonIdx = mortonAddr(child.pos, childSizeLog2);
+  }
 
   static const struct {
     int childIdxBitPos;
@@ -304,6 +310,10 @@ updateGeometryNeighState(
       continue;
     }
 
+    if (siblingRestriction)
+      continue;
+
+    uint64_t midx = child.mortonIdx = mortonAddr(child.pos, childSizeLog2);
     // calculate the morton address of the 'left' neighbour,
     // the delta is then used as the starting position for a search
     int64_t mortonIdxNeigh =

tmc3/PCCTMC3Decoder.h

@@ -183,7 +183,7 @@ private:
     geometryPointsAreUnique = bool(u8value);
 
     PCCReadFromBuffer<uint8_t>(bitstream.buffer, u8value, bitstream.size);
-    neighbourContextsEnabled = bool(u8value);
+    neighbourContextRestriction = bool(u8value);
 
     PCCReadFromBuffer<uint8_t>(bitstream.buffer, u8value, bitstream.size);
     inferredDirectCodingModeEnabled = bool(u8value);
@@ -478,18 +478,12 @@ private:
   // decode node occupancy bits
   //
   uint32_t decodeGeometryOccupancy(
-    bool neighbourContextsEnabled,
     o3dgc::Arithmetic_Codec* arithmeticDecoder,
     o3dgc::Adaptive_Bit_Model& ctxSingleChild,
     o3dgc::Static_Bit_Model& ctxEquiProb,
     CtxModelOctreeOccupancy& ctxOccupancy,
     const PCCOctree3Node& node0)
   {
-    if (!neighbourContextsEnabled) {
-      assert(0);  // todo(df): fixme -- we need an old context for this.
-      //return arithmeticDecoder->decode(ctxOccupancy[0]);
-    }
-
     // neighbouring configuration with reduction from 64 to 10
     int neighPattern = node0.neighPattern;
     int neighPattern10 = kNeighPattern64to10[neighPattern];
@@ -632,8 +626,8 @@ private:
 
       // decode occupancy pattern
       uint8_t occupancy = decodeGeometryOccupancy(
-        neighbourContextsEnabled, &arithmeticDecoder, ctxSingleChild,
-        ctxEquiProb, ctxOccupancy, node0);
+        &arithmeticDecoder, ctxSingleChild, ctxEquiProb, ctxOccupancy, node0);
+
       assert(occupancy > 0);
 
       // population count of occupancy for IDCM
@@ -704,11 +698,10 @@ private:
         }
 
         numNodesNextLvl++;
-        if (neighbourContextsEnabled) {
-          updateGeometryNeighState(
-            fifo.end(), numNodesNextLvl, childSizeLog2, child, i,
-            node0.neighPattern, occupancy);
-        }
+
+        updateGeometryNeighState(
+          neighbourContextRestriction, fifo.end(), numNodesNextLvl,
+          childSizeLog2, child, i, node0.neighPattern, occupancy);
       }
     }
 
@@ -750,7 +743,7 @@ private:
 
   // Controls the use of neighbour based contextualisation of octree
   // occupancy during geometry coding.
-  bool neighbourContextsEnabled;
+  bool neighbourContextRestriction;
 
   // Controls the use of early termination of the geometry tree
   // by directly coding the position of isolated points.

tmc3/PCCTMC3Encoder.h

@@ -63,13 +63,15 @@ struct PCCTMC3Encoder3Parameters {
   bool mergeDuplicatedPoints;
 
   // Controls the use of neighbour based contextualisation of octree
-  // occupancy during geometry coding.
-  bool neighbourContextsEnabled;
+  // occupancy during geometry coding.  When true, only neighbours that
+  // are direct siblings are available.
+  bool neighbourContextRestriction;
 
   // Controls the use of early termination of the geometry tree
   // by directly coding the position of isolated points.
   bool inferredDirectCodingModeEnabled;
 
+  bool skipNeighborSearch;
   struct TriSoup {
     // depth of voxels (reconstructed points) in trisoup geometry
     int depth;
@@ -465,7 +467,6 @@ private:
   // decode node occupancy bits
   //
   void encodeGeometryOccupancy(
-    bool neighbourContextsEnabled,
     o3dgc::Arithmetic_Codec* arithmeticEncoder,
     o3dgc::Adaptive_Bit_Model& ctxSingleChild,
     o3dgc::Static_Bit_Model& ctxEquiProb,
@@ -473,12 +474,6 @@ private:
     const PCCOctree3Node& node0,
     int occupancy)
   {
-    if (!neighbourContextsEnabled) {
-      assert(0);  // todo(df): fixme -- old contexts needed
-      // arithmeticEncoder->encode(occupancy, ctxOccupancy[0]);
-      return;
-    }
-
     // code occupancy using the neighbour configuration context
     // with reduction from 64 states to 10.
     int neighPattern = node0.neighPattern;
@@ -649,8 +644,8 @@ private:
       // encode child occupancy map
       assert(occupancy > 0);
       encodeGeometryOccupancy(
-        params.neighbourContextsEnabled, &arithmeticEncoder, ctxSingleChild,
-        ctxEquiProb, ctxOccupancy, node0, occupancy);
+        &arithmeticEncoder, ctxSingleChild, ctxEquiProb, ctxOccupancy, node0,
+        occupancy);
 
       // when nodeSizeLog2 == 1, children are indivisible (ie leaf nodes)
       // and are immediately coded.  No further splitting occurs.
@@ -727,11 +722,10 @@ private:
         }
 
         numNodesNextLvl++;
-        if (params.neighbourContextsEnabled) {
-          updateGeometryNeighState(
-            fifo.end(), numNodesNextLvl, childSizeLog2, child, i,
-            node0.neighPattern, occupancy);
-        }
+
+        updateGeometryNeighState(
+          params.neighbourContextRestriction, fifo.end(), numNodesNextLvl,
+          childSizeLog2, child, i, node0.neighPattern, occupancy);
       }
     }
 
@@ -782,7 +776,7 @@ private:
       uint8_t(params.mergeDuplicatedPoints), bitstream.buffer, bitstream.size);
 
     PCCWriteToBuffer<uint8_t>(
-      uint8_t(params.neighbourContextsEnabled), bitstream.buffer,
+      uint8_t(params.neighbourContextRestriction), bitstream.buffer,
       bitstream.size);
 
     PCCWriteToBuffer<uint8_t>(

tmc3/TMC3.cpp

@@ -244,9 +244,9 @@ ParseParameters(int argc, char* argv[], Parameters& params)
     "  1: octree (TMC3)\n"
     "  2: trisoup (TMC1)")
 
-  ("neighbourContextualisation",
-    params.encodeParameters.neighbourContextsEnabled, true,
-    "Contextualise geometry octree occupancy based on neighbour patterns")
+  ("neighbourContextRestriction",
+    params.encodeParameters.neighbourContextRestriction, false,
+    "Limit geometry octree occupancy contextualisation to sibling nodes")
 
   ("inferredDirectCodingMode",
     params.encodeParameters.inferredDirectCodingModeEnabled, true,