Add view control reference visual

[iche033]

Signed-off-by: Ian Chen ichen@osrfoundation.org

🎉 New feature

related issue: https://github.com/gazebosim/gz-rendering/issues/265

related PR: https://github.com/gazebosim/gz-sim/pull/1788

Summary

Adds a reference visual to help visualize the anchor point for view control operations.

The implementation is done in gz-gui instead of gz-rendering as it's easier to do since we need to toggle visibility depending on mouse events, and also we don't need to write the same code twice for different view controllers.

By default, the visual is enabled. You can enable / disable this visual with https://github.com/gazebosim/gz-sim/pull/1788.

side note: I tried testing with the orthographic view controller, but the controller seems to be broken

Test it

Launch gazebo and try panning, orbiting, zooming with the mouse and you should see a small yellow ellipsoid rendered at the mouse press position.

Checklist

• [x] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] Consider updating Python bindings (if the library has them)
• [ ] 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 and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov[bot]]

Codecov Report

Merging #500 (69e3089) into ign-gui6 (4232d2a) will decrease coverage by 0.51%. The diff coverage is 10.63%.

@@             Coverage Diff              @@
##           ign-gui6     #500      +/-   ##
============================================
- Coverage     68.00%   67.49%   -0.52%     
============================================
  Files            39       39              
  Lines          5239     5286      +47     
============================================
+ Hits           3563     3568       +5     
- Misses         1676     1718      +42     

Impacted Files	Coverage Δ
...interactive_view_control/InteractiveViewControl.cc	15.88% <10.63%> (-2.01%)	:arrow_down:

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