alice_esd.js

// function to extract tracks from ALICE_ESD tree
// tracks are in https://root.cern/files/alice_ESDs.root
// geometry in https://root.cern/files/alice_ESDgeometry.root

function extract_geo_tracks(tree, opt, call_back) {
   // as first argument, tree should be provided

   console.log('CALL extract_geo_tracks');

   var selector = new JSROOT.TSelector();

   selector.AddBranch("ESDfriend.fTracks.fPoints","pnts");

   var lst = JSROOT.Create("TList"), numentry = 0, numtracks = 0;

   selector.Process = function() {
      // function called for every entry

      var pnts = this.tgtobj.pnts;

      numentry++;

      // now converts AliTrackPointArray into TGeoTrack
      for (var p=0;p<pnts.length;++p) {
         numtracks++;
         var arr = pnts[p];
         if (!arr.fNPoints) continue;
         var track = JSROOT.Create("TGeoTrack");
         track.fNpoints = arr.fNPoints;
         track.fPoints = new Float32Array(track.fNpoints*3);
         for (var k=0;k<track.fNpoints;++k) {
            track.fPoints[k*3] = arr.fX[k];
            track.fPoints[k*3+1] = arr.fY[k];
            track.fPoints[k*3+2] = arr.fZ[k];
         }
         track.fLineWidth = 2;
         track.fLineColor = 3;
         lst.Add(track);
         if (numtracks>100) return this.Abort(); // do not accumulate too many tracks
      }
   }

   selector.Terminate = function(res) {
      // function called when processing finishes
      console.log('Read done num entries', numentry, 'tracks', numtracks);
      JSROOT.CallBack(call_back, lst);
   }

   tree.Process(selector);
}

console.log('LOAD alice_esd.js JSROOT', JSROOT.version);