Get features for multiple blocks when axis brush.

axis-tracks.js : layoutWidth() :  use trackBlocksR in place of trackBlocks.

paths-progressive.js : requestBlockFeaturesInterval() : call getBlockFeaturesInterval() once for each blockId; see comments for background;  previously the results were limited to a single block.
backend/common/utilities/ :
 69591ee  1288 Sep  8 13:59  block-features.js
 62b68d1 28235 Sep  8 16:39  paths-aggr.js
frontend/app/ :
 202df14 24528 Sep  6 17:52  components/axis-tracks.js
 515fde4 22795 Sep  8 16:08  services/data/paths-progressive.js

backend/common/utilities/block-features.js

@@ -36,7 +36,7 @@ exports.blockFeaturesCount = function(db, blockIds) {
     pipeline = matchBlock;
 
   if (trace_block)
-    console.log('blockFeaturesInterval', pipeline);
+    console.log('blockFeaturesCount', pipeline);
   if (trace_block > 1)
     console.dir(pipeline, { depth: null });
 

backend/common/utilities/paths-aggr.js

@@ -601,6 +601,11 @@ function pipelineLimits(featureCollection, intervals, pipeline) {
  *
  * @param blockCollection dataSource collection
  * @param blockIds  ids of data blocks
+ *
+ * As commented in requestBlockFeaturesInterval(), using $sample will result in
+ * only 1 blockId in the result, so this function is called once for each
+ * blockId.
+ *
  * @param intervals  domain and range of axis of block, to limit the number of features in result.
 
  * @return cursor	: features
@@ -612,6 +617,13 @@ exports.blockFeaturesInterval = function(db, blockIds, intervals) {
     console.log('blockFeaturesInterval', /*featureCollection,*/ blockIds, intervals);
   let ObjectId = ObjectID;
 
+  /** When called from axis-brush:features(), the blocks being looked up are
+   * on the same axis, and hence interval domain is the same;    blockFilters will
+   * repeat the domain constraint for each block, but instead matchBlock could
+   * be used, in combination with a single domain constraint;  but this is a
+   * moot point because blockIds[] is only called with a single element - see
+   * comment above.
+   */
   let
     matchBlock =
     [

frontend/app/components/axis-tracks.js

@@ -594,8 +594,8 @@ export default InAxis.extend({
   }),
   layoutWidth : Ember.computed('trackBlocks.[]', function () {
     let
-    trackBlocks = this.get('trackBlocks'),
-    blockIds = trackBlocks.map(function (block) { return block.axisName; }),
+    trackBlocksR = this.get('trackBlocksR'),
+    blockIds = trackBlocksR.mapBy('id'),
     /** Add 50 on the right to avoid clashing with the right axis ticks text,
      * which may later be switched off with CSS.
      * this includes xOffset from blockTransform(blockIds.length-1) 

frontend/app/services/data/paths-progressive.js

@@ -565,11 +565,21 @@ export default Service.extend({
     let dataBlockIds = axis.dataBlocks(true)
      // equiv : blockS.block.get('id')
       .map(function (blockS) { return blockS.axisName; });
+    /** The result of passing multiple blockIds to getBlockFeaturesInterval()
+     * has an unevenly distributed result : all the results come from just 1 of
+     * the blockIds.  This is because of the implementation of $sample
+     * (https://stackoverflow.com/a/46881483).
+     * So instead getBlockFeaturesInterval() is called once for each blockId;
+     * requestBlockIds is used in place of dataBlockIds.
+     */
+    let promises =
+    dataBlockIds.map(function (blockId) {
+      let requestBlockIds = [blockId];
     let promise = 
       // streaming version not added yet
       // pathsViaStream ?
       // this.get('auth').getPathsViaStream(blockA, blockB, intervalParams, /*options*/{dataEvent : receivedData}) :
-      this.get('auth').getBlockFeaturesInterval(dataBlockIds, intervalParams, /*options*/{});
+      me.get('auth').getBlockFeaturesInterval(requestBlockIds, intervalParams, /*options*/{});
         function receivedData(res){
           if (trace_pathsP > 1)
             console.log(apiName, ' request then', res.length);
@@ -586,7 +596,7 @@ export default Service.extend({
 
           Ember.run.throttle(
             me, me.blocksUpdateDomain, 
-            dataBlockIds, domainCalc, axisEvents,
+            requestBlockIds, domainCalc, axisEvents,
             200, false);
         };
     promise
@@ -598,6 +608,8 @@ export default Service.extend({
           // else
             console.log(apiName, ' request', blockA, me, err.responseJSON[status] /* .error.message*/, status);
         });
+    });
+    let promise = Ember.RSVP.allSettled(promises);
     return promise;
 
   }