attr/m49630: permit unconditional signalling of prediction index

This adoption permits removal of an arithmetic coding dependency in the
predicting lod scheme when lifting_adaptive_prediction_threshold is
equal to 0.

tmc3/AttributeDecoder.cpp

@@ -234,6 +234,8 @@ AttributeDecoder::computeReflectancePredictionWeights(
   PCCResidualsDecoder& decoder)
 {
   predictor.computeWeights();
+  int64_t maxDiff = 0;
+
   if (predictor.neighborCount > 1) {
     int64_t minValue = 0;
     int64_t maxValue = 0;
@@ -247,11 +249,11 @@ AttributeDecoder::computeReflectancePredictionWeights(
         maxValue = reflectanceNeighbor;
       }
     }
-    const int64_t maxDiff = maxValue - minValue;
-    if (maxDiff > aps.adaptive_prediction_threshold) {
-      predictor.predMode =
-        decoder.decodePredMode(aps.max_num_direct_predictors);
-    }
+    maxDiff = maxValue - minValue;
+  }
+
+  if (maxDiff >= aps.adaptive_prediction_threshold) {
+    predictor.predMode = decoder.decodePredMode(aps.max_num_direct_predictors);
   }
 }
 
@@ -314,6 +316,8 @@ AttributeDecoder::computeColorPredictionWeights(
   PCCResidualsDecoder& decoder)
 {
   predictor.computeWeights();
+  int64_t maxDiff = 0;
+
   if (predictor.neighborCount > 1) {
     int64_t minValue[3] = {0, 0, 0};
     int64_t maxValue[3] = {0, 0, 0};
@@ -329,13 +333,13 @@ AttributeDecoder::computeColorPredictionWeights(
         }
       }
     }
-    const int64_t maxDiff = (std::max)(
+    maxDiff = (std::max)(
       maxValue[2] - minValue[2],
       (std::max)(maxValue[0] - minValue[0], maxValue[1] - minValue[1]));
-    if (maxDiff > aps.adaptive_prediction_threshold) {
-      predictor.predMode =
-        decoder.decodePredMode(aps.max_num_direct_predictors);
-    }
+  }
+
+  if (maxDiff >= aps.adaptive_prediction_threshold) {
+    predictor.predMode = decoder.decodePredMode(aps.max_num_direct_predictors);
   }
 }
 

tmc3/AttributeEncoder.cpp

@@ -407,7 +407,7 @@ AttributeEncoder::computeReflectancePredictionWeights(
   const int64_t qs)
 {
   predictor.computeWeights();
-  predictor.maxDiff = -1;
+  predictor.maxDiff = 0;
   if (predictor.neighborCount > 1) {
     int64_t minValue = 0;
     int64_t maxValue = 0;
@@ -423,7 +423,7 @@ AttributeEncoder::computeReflectancePredictionWeights(
     }
     const int64_t maxDiff = maxValue - minValue;
     predictor.maxDiff = maxDiff;
-    if (maxDiff > aps.adaptive_prediction_threshold) {
+    if (maxDiff >= aps.adaptive_prediction_threshold) {
       uint64_t attrValue =
         pointCloud.getReflectance(indexesLOD[predictorIndex]);
 
@@ -530,7 +530,7 @@ AttributeEncoder::encodeReflectancesPred(
   for (size_t predictorIndex = 0; predictorIndex < pointCount;
        ++predictorIndex) {
     auto& predictor = predictors[predictorIndex];
-    if (predictor.maxDiff > aps.adaptive_prediction_threshold) {
+    if (predictor.maxDiff >= aps.adaptive_prediction_threshold) {
       encoder.encodePredMode(
         predictor.predMode, aps.max_num_direct_predictors);
     }
@@ -585,7 +585,7 @@ AttributeEncoder::computeColorPredictionWeights(
   const int64_t qs2)
 {
   predictor.computeWeights();
-  predictor.maxDiff = -1;
+  predictor.maxDiff = 0;
   if (predictor.neighborCount > 1) {
     int64_t minValue[3] = {0, 0, 0};
     int64_t maxValue[3] = {0, 0, 0};
@@ -606,7 +606,7 @@ AttributeEncoder::computeColorPredictionWeights(
       (std::max)(maxValue[0] - minValue[0], maxValue[1] - minValue[1]));
     predictor.maxDiff = maxDiff;
 
-    if (maxDiff > aps.adaptive_prediction_threshold) {
+    if (maxDiff >= aps.adaptive_prediction_threshold) {
       Vec3<uint8_t> attrValue =
         pointCloud.getColor(indexesLOD[predictorIndex]);
 
@@ -734,7 +734,7 @@ AttributeEncoder::encodeColorsPred(
   for (size_t predictorIndex = 0; predictorIndex < pointCount;
        ++predictorIndex) {
     auto& predictor = predictors[predictorIndex];
-    if (predictor.maxDiff > aps.adaptive_prediction_threshold) {
+    if (predictor.maxDiff >= aps.adaptive_prediction_threshold) {
       encoder.encodePredMode(
         predictor.predMode, aps.max_num_direct_predictors);
     }