# submaps_display.cpp

`src/submaps_display.cpp` implements the `SubmapsDisplay` plugin and the `Trajectory` helper struct declared in `submaps_display.h`. It is the main entry point of the package and is registered as an RViz display plugin at the bottom:

```cpp
PLUGINLIB_EXPORT_CLASS(cartographer_rviz::SubmapsDisplay, rviz_common::Display)
```

## Constants

- `kMaxOnGoingRequestsPerTrajectory = 6` — caps concurrent texture queries per trajectory.
- `kMaterialsDirectory`, `kGlsl120Directory`, `kScriptsDirectory` — sub-paths under the installed package share directory used to locate the OGRE resources.
- `kDefaultTrackingFrame = "base_link"` — default tracking frame.
- `kDefaultSubmapQueryServiceName = "/submap_query"` — default service used to fetch textures.

## Constructor

The constructor sets up the RViz properties:

- `Submap query service` (StringProperty) — triggers `Reset()` when changed.
- `Tracking frame` (StringProperty) — used for fading out submaps.
- `High Resolution` (BoolProperty, default `true`) and `Low Resolution` (BoolProperty, default `false`) — both connected to `ResolutionToggled()`.
- `Submaps` category with `All` and `All Submap Pose Markers` toggles.
- `Fade-out distance` (FloatProperty, default `1.f`).

It creates a mutually-exclusive callback group and a dedicated `SingleThreadedExecutor`, then creates the `SubmapQuery` service client (QoS defaults differ by `rclcpp` version). It registers the package's `ogre_media/materials`, `.../glsl120`, and `.../scripts` directories with the OGRE resource manager and initialises the resource groups. Finally it creates a TF2 buffer and transform listener.

## Lifecycle

- `onInitialize()` calls the base class, creates the `map_node_` scene node at the root, and creates the client.
- `reset()` clears the client and all trajectories, then re-creates the client.
- The destructor resets the client, clears trajectories, and destroys `map_node_`.

## processMessage

Called for every `SubmapList` message:

1. Records the map frame from the header.
2. If any listed submap reports a version older than what is already displayed (meaning the Cartographer node was relaunched), all trajectories are cleared.
3. For every `SubmapEntry`, it creates a `Trajectory` (if new) and a `DrawableSubmap` (if new), enabling the high/low resolution slices per the current property values, and calls `Update()` with the header and entry.
4. Trajectories and submaps no longer present in the message are removed.

## update

Called each render frame:

- Iterates trajectories, counting in-flight queries, and calls `MaybeFetchTexture()` on submaps in reverse order until `kMaxOnGoingRequestsPerTrajectory` is reached.
- Looks up the transform from the map frame to the tracking frame (with a 100 ms timeout) and calls `SetAlpha()` on every submap to fade by z distance; logs a warning if the transform fails.
- Applies the map-frame-to-fixed-frame transform to `map_node_`.

## Property toggles

- `AllEnabledToggled()` / `PoseMarkersEnabledToggled()` propagate the global toggles to all trajectories.
- `ResolutionToggled()` sets slice visibility on every submap.

## Trajectory

`Trajectory::Trajectory(...)` moves the visibility property in, connects its `changed()` signal to `AllEnabledToggled()`, and adds a `Submap Pose Markers` child property connected to `PoseMarkersEnabledToggled()`. Both slots propagate the toggle to each `DrawableSubmap` in the trajectory.