Performer count

[nkoenig]

🎉 New feature

Summary

The performer detector will send information about when a performer enters or leaves a region, but does not include the number of entities in the region. The count is useful when, for example, a user wants to turn off a fog emitter only when the last robot leaves a region.

Test it

1. ign gazebo -v 4 performer_detector.sdf
2. ign topic -t "/model/vehicle_blue/cmd_vel" -m ignition.msgs.Twist -p "linear: {x: 0.5}"
3. ign topic -et /performer_detector

You should see the following when the robot enters the region:

   data {
    key: "count"
    value: "1"
  }

and this when the robot leaves

   data {
    key: "count"
    value: "0"
  }

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[iche033]

fixed a small typo. 7554335

Looks good to me.

[codecov]

Codecov Report

Merging #652 (a38ff58) into ign-gazebo4 (1a16084) will decrease coverage by 0.03%.
The diff coverage is 73.94%.

@@               Coverage Diff               @@
##           ign-gazebo4     #652      +/-   ##
===============================================
- Coverage        64.77%   64.74%   -0.04%     
===============================================
  Files              232      232              
  Lines            16590    16619      +29     
===============================================
+ Hits             10747    10760      +13     
- Misses            5843     5859      +16     

Impacted Files	Coverage Δ
...rc/systems/performer_detector/PerformerDetector.hh	100.00% <ø> (ø)
src/systems/physics/Physics.cc	71.15% <73.27%> (-0.30%)	⬇️
...rc/systems/performer_detector/PerformerDetector.cc	88.07% <100.00%> (+0.33%)	⬆️
src/SimulationRunner.cc	92.88% <0.00%> (-1.07%)	⬇️

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