C++ example for mcap using RangedPlayback

[ericmlujan]

Changelog

• Add C++ example for using the RangedPlayback capability

Docs

• This is an example.

Description

Add a C++ example using the RangedPlayback websocket capability to load and play back an mcap file. This example introduces an annotated PlaybackSource base class, which others can pattern match to when implementing their own loaders for custom data formats.

This PR ports #859.

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

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[cursor]

Incomplete status check in pause function

Low Severity

The pause() function checks status_ == foxglove::PlaybackStatus::Ended but not whether status is already Paused. When called while already paused, it unnecessarily calls time_tracker_->pause() and redundantly sets status_. The condition should be status_ != foxglove::PlaybackStatus::Playing to properly short-circuit when not actively playing. This matches the semantic intent of "pause playback" which only applies when playback is happening.

 

[cursor]

Incomplete status check in play function

Low Severity

The play() function checks status_ == foxglove::PlaybackStatus::Ended but not whether status is already Playing. When called while already playing, it unnecessarily calls time_tracker_->resume() and redundantly sets status_. The condition should be status_ != foxglove::PlaybackStatus::Paused to properly short-circuit when not in a paused state. This is the same logical incompleteness as the pause() function.