[SLAM] FPS of occupancy map update of JS is much slower than native

[haoyunfeix]

In JS version of slam_tutorial_1_web:

let slamModule = require('slam');

const mapResolution = 0.025;

let slam;
slamModule.createInstance().then((instance) => {
  startServer();
  slam = instance;

  let slamOptions = {
    occupancyMapResolution: mapResolution,
  };
  return slam.setInstanceOptions(slamOptions);
}).then(() => {
  console.log('Starting SLAM...');
  slam.on('tracking', (result) => {
    slam.getOccupancyMapUpdate().then((mapData) => {
      if (mapData.tileCount <= 0) {
        // occupancy map is updated.
        return;
      }
    });

  });
  return slam.start();
}).catch((error) => {
  console.log('error: ' + error);
});

The occupancy map update FPS of getOccupancyMapUpdate JS API is less than 1 FPS.

In C++ version:

class slam_event_handler : public video_module_interface::processing_event_handler
{
public:
    slam_event_handler() {}
    ~slam_event_handler() = default;

    void module_output_ready(video_module_interface* sender,
                             correlated_sample_set* sample)
    {
        slam* slam_module = dynamic_cast<slam*>(sender);
        if (!occupancy)
        {
            //
            occupancy = slam_module->create_occupancy_map(50 * 50);
            occupancy_res = slam_module->get_occupancy_map_resolution();
        }

        auto occ_status = slam_module->get_occupancy_map_update(occupancy);
        int count = occupancy->get_tile_count();
        if (occ_status >= status::status_no_error && count > 0)
        {
            // occupancy map is updated
        }
    }
};

In similar test environment, the native get_occupancy_map_update API update rate is about 8 FPS.