Fix loading grayscale emissive map

[iche033]

🦟 Bug fix

Fixes #499

Summary

Continuing the effort from #501, this PR fixes loading grayscale emissive map by converting it to RGB color texture so that the visual with the emissive map is not incorrectly rendered as red color.

Test by lauching ign gazebo with the fuel_textured_mesh.sdf world file.

Before:

After:

Alternative considered

The other option considered is to some customization in the Pbs Hlms pixel shader and just apply only the r channel of the emissive texture to the final color, .e.g. changing the code here to finalColour += emissiveCol.rrr;.

I went with the approach in this PR mainly to keep the changes within one function without touching the shaders so we don't deviate too much from the original Pbs shader code we took from ogre. This approach was also easier for me to to implement.

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)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[codecov]

Codecov Report

Merging #503 (a6796ac) into ign-rendering6 (f025610) will decrease coverage by 0.08%.
The diff coverage is 15.00%.

@@                Coverage Diff                 @@
##           ign-rendering6     #503      +/-   ##
==================================================
- Coverage           55.53%   55.44%   -0.09%     
==================================================
  Files                 195      195              
  Lines               19698    19736      +38     
==================================================
+ Hits                10939    10943       +4     
- Misses               8759     8793      +34     

Impacted Files	Coverage Δ
ogre2/src/Ogre2Material.cc	84.30% <15.00%> (-7.86%)	⬇️

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[darksylinc]

Sounds like this is something that should be fixed from Upstream?

Detect if emissive is greyscale, then use a shader with the right swizzle

Update: Added fix to upstream. Remember to update C++ and copy shader files to ignition's.

[iche033]

great, thanks for implementing grayscale emissive map support upstream! I'm going to try get this in first, and remove later when I get time to port the fix over to our fork (and package / release new debs etc)