Make particle emitter invisible in thermal camera image

[iche033]

Summary

Achieved by setting visibility mask and flags. The thermal camera now has a visibility mask that does not match with the visibility flags of the particle emitter.

Example output in ign-gazebo. Left: RGBD camera that sees the particles. Right: Thermal camera that only sees Rescue Randy but not the particles emitted by the particle emitter.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See
  contributing)
• All tests passed (See test coverage)
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[codecov]

Codecov Report

Merging #240 (c0d4ef0) into ign-rendering4 (938e42c) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@                Coverage Diff                 @@
##           ign-rendering4     #240      +/-   ##
==================================================
+ Coverage           52.88%   52.92%   +0.03%     
==================================================
  Files                 143      143              
  Lines               13563    13566       +3     
==================================================
+ Hits                 7173     7180       +7     
+ Misses               6390     6386       -4     

Impacted Files	Coverage Δ
ogre2/src/Ogre2ParticleEmitter.cc	77.77% <100.00%> (+1.12%)	⬆️
ogre2/src/Ogre2ThermalCamera.cc	90.75% <100.00%> (+0.05%)	⬆️
...ude/ignition/rendering/base/BaseParticleEmitter.hh	44.15% <0.00%> (+2.59%)	⬆️

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[adlarkin]

Changes look good. Is there an example world you used to test this, and are any other PRs required to test these changes? I'd like to run a local test as a sanity check before approving.

[iche033]

here's the world sdf file I used for testing: https://gist.githubusercontent.com/iche033/2be422b8c527461b1a9cf9788ccf3967/raw/7f2c36757a28c5cda43442016732dd058df6310e/thermal_particles.sdf

[adlarkin]

I'm seeing some weird rendering effects - it looks like the shape of the particles are always rendered relative to the way I view it in the GUI (animation attached below - notice how the box seems to rotate with the GUI display). I don't think this is related to this PR, but do you see something like this as well? Or is this expected behavior?

[iche033]

yes that's the expected behavior. Particles are rendered as 2D sprites / billboards in ogre (and also commonly done in other render engines, e.g. threejs example). They always face the camera and are always upright.