code: function marker(markers, group, options) {
          var activation = group.activation; // reset marker elements
  
          activation.forEach(function (buffer) {
            return buffer && buffer.destroy && buffer.destroy();
          });
          activation.length = 0; // single sdf marker
  
          if (!markers || typeof markers[0] === 'number') {
            var id = _this3.addMarker(markers);
  
            activation[id] = true;
          } // per-point markers use mask buffers to enable markers in vert shader
          else {
              var markerMasks = [];
  
              for (var _i = 0, l = Math.min(markers.length, group.count); _i < l; _i++) {
                var _id = _this3.addMarker(markers[_i]);
  
                if (!markerMasks[_id]) markerMasks[_id] = new Uint8Array(group.count); // enable marker by default
  
                markerMasks[_id][_i] = 1;
              }
  
              for (var _id2 = 0; _id2 < markerMasks.length; _id2++) {
                if (!markerMasks[_id2]) continue;
                var opts = {
                  data: markerMasks[_id2],
                  type: 'uint8',
                  usage: 'static'
                };
  
                if (!activation[_id2]) {
                  activation[_id2] = regl.buffer(opts);
                } else {
                  activation[_id2](opts);
                }
  
                activation[_id2].data = markerMasks[_id2];
              }
            }
  
          return markers;
        }
docs: create marker ids corresponding to known marker textures