Be consistent in RGB channel notation for ogre2 segmentation camera

[adlarkin]

Signed-off-by: Ashton Larkin ashton@openrobotics.org

🦟 Bug fix

Summary

When we updated the segmentation sensor (#329) to ogre2.2, it looks like inconsistencies were introduced in what pixel channels were considered RGB.

In Ogre2SegmentationCamera::LabelMapFromColoredBuffer, the notation is GBR: https://github.com/ignitionrobotics/ign-rendering/blob/7aade51f83171f2ada47089e6f8594fc3ccdddc5/ogre2/src/Ogre2SegmentationCamera.cc#L371-L373

But, in the material switcher, RGB is used:
https://github.com/ignitionrobotics/ign-rendering/blob/7aade51f83171f2ada47089e6f8594fc3ccdddc5/ogre2/src/Ogre2SegmentationMaterialSwitcher.cc#L233-L234
https://github.com/ignitionrobotics/ign-rendering/blob/7aade51f83171f2ada47089e6f8594fc3ccdddc5/ogre2/src/Ogre2SegmentationMaterialSwitcher.cc#L280-L281

This PR updates the indexing in Ogre2SegmentationCamera::LabelMapFromColoredBuffer to RGB instead of GBR.

Making this update fixes the label map data produced in gazebosim/gz-sensors#133. Before, the segmentation labels map was an image with all pixels set to the background label. Now, labels appear correctly:

Checklist

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

@iche033 do you think it's better to update the Ogre::Vector4s in the material switcher to be GBR instead of RGB, or is it best to leave those as RGB and update the indexing in Ogre2SegmentationCamera::LabelMapFromColoredBuffer? I tested both, and they each seem to work fine.

[codecov]

Codecov Report

Merging #419 (d2945ca) into main (8e7c876) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main     #419   +/-   ##
=======================================
  Coverage   55.06%   55.06%           
=======================================
  Files         191      191           
  Lines       19265    19265           
=======================================
  Hits        10608    10608           
  Misses       8657     8657           

Impacted Files	Coverage Δ
ogre2/src/Ogre2SegmentationCamera.cc	75.67% <0.00%> (ø)

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