geom: unify encoder and decoder internal point representation

This commit changes the representation of quantised points in the
encoder to be 'MSB' justified, as is the case in the decoder.
Quantised points now take the form "0bppppppqqq00" where p denotes
unquantised bits, q quantised bits, and 0 marks non coded bits.

tmc3/geometry_octree_encoder.cpp

@@ -106,6 +106,7 @@ public:
 
   bool encodeDirectPosition(
     const Vec3<int>& nodeSizeLog2,
+    int shiftBits,
     const PCCOctree3Node& node,
     const PCCPointSet3& pointCloud);
 
@@ -501,9 +502,9 @@ geometryQuantization(
       uint32_t quantPos = quantizer.quantize(pos & quantBitsMask);
       quantPos = PCCClip(quantPos, 0, clipMax);
 
-      // NB: this representation is: |pppppp00qqq|, which isn't the
-      // same used by the decoder:  (|ppppppqqq|00)
-      pointCloud[i][k] = (pos & ~quantBitsMask) | quantPos;
+      // NB: this representation is: |ppppppqqq|00, which is the
+      // same as the decoder
+      pointCloud[i][k] = (pos & ~quantBitsMask) | (quantPos << qpShift);
     }
   }
 }
@@ -521,7 +522,7 @@ geometryScale(
     int quantBitsMask = (1 << quantNodeSizeLog2[k]) - 1;
     for (int i = node.start; i < node.end; i++) {
       uint32_t pos = uint32_t(pointCloud[i][k]);
-      uint32_t quantPos = pos & quantBitsMask;
+      uint32_t quantPos = (pos >> qpShift) & quantBitsMask;
       pointCloud[i][k] = (pos & ~quantBitsMask) | quantizer.scale(quantPos);
     }
   }
@@ -556,6 +557,7 @@ checkDuplicatePoints(
 bool
 GeometryOctreeEncoder::encodeDirectPosition(
   const Vec3<int>& nodeSizeLog2,
+  int shiftBits,
   const PCCOctree3Node& node,
   const PCCPointSet3& pointCloud)
 {
@@ -573,7 +575,8 @@ GeometryOctreeEncoder::encodeDirectPosition(
       nodeSizeLog2,
       Vec3<uint32_t>{uint32_t(pointCloud[idx][0]),
                      uint32_t(pointCloud[idx][1]),
-                     uint32_t(pointCloud[idx][2])});
+                     uint32_t(pointCloud[idx][2])}
+        >> shiftBits);
   }
 
   return true;
@@ -750,9 +753,9 @@ encodeGeometryOctree(
       PCCPointSet3::iterator(&pointCloud, node0.end), childCounts,
       [=](const PCCPointSet3::Proxy& proxy) {
         const auto& point = *proxy;
-        return !!(int(point[2]) & (pointSortMask[2] >> shiftBits))
-          | (!!(int(point[1]) & (pointSortMask[1] >> shiftBits)) << 1)
-          | (!!(int(point[0]) & (pointSortMask[0] >> shiftBits)) << 2);
+        return !!(int(point[2]) & pointSortMask[2])
+          | (!!(int(point[1]) & pointSortMask[1]) << 1)
+          | (!!(int(point[0]) & pointSortMask[0]) << 2);
       });
 
     // generate the bitmap of child occupancy and count
@@ -883,7 +886,7 @@ encodeGeometryOctree(
       if (isDirectModeEligible(
             idcmEnabled, effectiveNodeMaxDimLog2, node0, child)) {
         bool directModeUsed = encoder.encodeDirectPosition(
-          effectiveChildSizeLog2, child, pointCloud);
+          effectiveChildSizeLog2, shiftBits, child, pointCloud);
 
         if (directModeUsed) {
           // inverse quantise any quantised positions