cfg: automatic derivation of dist2 series

This commit introduces automatic derivation of dist2 values by the
frontend.  Automatic derivation occurs if fewer than levelOfDetailCount
values are provided.  No syntax changes are made.

cfg update:
 - use single dist2 values based on existing config
 - ford: 16383 -> 16384

cfg/cat3-tmc13-ctc-lossless-geom-lossless-attrs.yaml

@@ -29,7 +29,7 @@ categories:
          - &mitsubishiLosslessAttrs
             - numberOfNearestNeighborsInPrediction: 3
             - levelOfDetailCount: 9
-            - dist2: 134217728 33554432 8388608 2097152 524288 131072 32768 8192 0
+            - dist2: 8192
             - quantizationStepLuma: 0
             - quantizationStepChroma: 0
          - bitdepth: 8
@@ -88,7 +88,7 @@ categories:
          - &fordLosslessAttrs
             - numberOfNearestNeighborsInPrediction: 3
             - levelOfDetailCount: 6
-            - dist2: 4194301 1048582 262149 65534 16383 0
+            - dist2: 16384
             - quantizationStepLuma: 0
          - bitdepth: 8
          - attribute: reflectance

cfg/cat3-tmc13-ctc-lossless-geom-lossy-attrs.yaml

@@ -30,7 +30,7 @@ categories:
          - &commonAttr
            - numberOfNearestNeighborsInPrediction: 3
            - levelOfDetailCount: 9
-           - dist2: 134217728 33554432 8388608 2097152 524288 131072 32768 8192 0
+           - dist2: 8192
          - quantizationStepLuma:
              r01: 256
              r02: 128

cfg/cat3-tmc13-ctc-lossless-geom-nearlossless-attrs.yaml

@@ -30,7 +30,7 @@ categories:
          - &mitsubishiNearlosslessAttrs
             - numberOfNearestNeighborsInPrediction: 3
             - levelOfDetailCount: 9
-            - dist2: 134217728 33554432 8388608 2097152 524288 131072 32768 8192 0
+            - dist2: 8192
          - &mitsubishiNearlosslessAttrsColour8
             - *mitsubishiNearlosslessAttrs
             - quantizationStepLuma:
@@ -101,7 +101,7 @@ categories:
          - &fordNearlosslessAttrsRefl8
             - numberOfNearestNeighborsInPrediction: 3
             - levelOfDetailCount: 6
-            - dist2: 4194301 1048582 262149 65534 16383 0
+            - dist2: 16384
             - quantizationStepLuma:
                 r01: 2
                 r02: 4

cfg/cat3-tmc13-ctc-lossy-geom-lossy-attrs.yaml

@@ -34,12 +34,12 @@ categories:
              r05: 6
              r06: 6
          - dist2:
-             r01:      6     0
-             r02:     21     5     1    0
-             r03:     85    21     5    1    0
-             r04:    508   127    32    8    2 0
-             r05:  10486  2621   655  164   41 0
-             r06: 317194 79299 19825 4956 1239 0
+             r01: 6
+             r02: 1
+             r03: 1
+             r04: 2
+             r05: 41
+             r06: 1239
          - quantizationStepLuma: 8
          - bitdepth: 8
          - attribute: reflectance

tmc3/TMC3.cpp

@@ -352,7 +352,8 @@ ParseParameters(int argc, char* argv[], Parameters& params)
 
   ("dist2",
     params_attr.aps.dist2, {},
-    "Attribute's list of squared distances (one for each LoD)")
+    "Attribute's list of squared distances, or initial value for automatic"
+    "derivation")
   ;
   /* clang-format on */
 
@@ -390,6 +391,25 @@ ParseParameters(int argc, char* argv[], Parameters& params)
       attr_aps.quant_step_size_chroma = 0;
     }
 
+    bool isLifting =
+      attr_aps.attr_encoding == AttributeEncoding::kPredictingTransform
+      || attr_aps.attr_encoding == AttributeEncoding::kLiftingTransform;
+
+    // derive the dist2 values based on an initial value
+    if (isLifting && !attr_aps.dist2.empty()) {
+      if (attr_aps.dist2.size() < attr_aps.numDetailLevels) {
+        attr_aps.dist2.resize(attr_aps.numDetailLevels);
+        const double distRatio = 4.0;
+        uint64_t d2 = attr_aps.dist2[0];
+
+        for (int i = 1; i < attr_aps.numDetailLevels; ++i) {
+          attr_aps.dist2[attr_aps.numDetailLevels - 1 - i] = d2;
+          d2 = uint64_t(std::round(distRatio * d2));
+        }
+        attr_aps.dist2[attr_aps.numDetailLevels - 1] = 0;
+      }
+    }
+
     // Set default threshold based on bitdepth
     if (attr_aps.adaptive_prediction_threshold == -1) {
       attr_aps.adaptive_prediction_threshold = 1
@@ -433,9 +453,9 @@ ParseParameters(int argc, char* argv[], Parameters& params)
     if (isLifting) {
       int lod = attr_aps.numDetailLevels;
 
-      if (lod > 255) {
+      if (lod > 255 || lod < 1) {
         err.error() << it.first
-                    << ".levelOfDetailCount must be less than 256\n";
+                    << ".levelOfDetailCount must be in the range [1,255]\n";
       }
       if (attr_aps.dist2.size() != lod) {
         err.error() << it.first << ".dist2 does not have " << lod