Fix Ogre2RenderTarget::TargetFSAA method that caused black screen when used with llvmpipe (i.e. software rendering on Linux)

[traversaro]

The Ogre2RenderTarget::TargetFSAA method has a logic to check if the selected antialiasing level is supported.

If the requested antialiasing level is not supported, the 0 level is selected instead. Furthermore, a warning is printed only once for process. Before this PR, the 0 level was only set only when the warning was printed, resulting in an unsupported antialiasing being set if Ogre2RenderTarget::TargetFSAA was called two or more times.

🦟 Bug fix

Fixes gazebosim/gz-sim#1116 .

Summary

Before this fix, running LIBGL_ALWAYS_SOFTWARE=1 ign gazebo shapes.sdf --verbose with a recent enough mesa (for example the one provided by default in Ubuntu 22.04) resulted in a black screen in the render area. With this fix, everything works is rendered correctly.

Checklist

• Signed all commits for DCO
• Added tests
• 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.

[traversaro]

As the bug was introduced (I think) in https://github.com/gazebosim/gz-rendering/pull/272/files#diff-d0c4d95c8bb6f3ff2d80c1c9b72dc8c4d5635d31d3a71d4d75bb3b4dca632407L488, thecode in Ogre1 and Ignition Citadel is not affected by this problem, so no other PRs are required:

• https://github.com/gazebosim/gz-rendering/blob/ign-rendering3/ogre2/src/Ogre2RenderTarget.cc#L820
• https://github.com/gazebosim/gz-rendering/blob/ign-rendering6/ogre/src/OgreRenderTarget.cc#L364

Other parts of the code can be improved (the warning should be printed again if a SetAliasing with a different value is called or a SetAliasing on a different instance, why the aa value is hardcoded to 1 if 0 is actually selected). However, this problems can be discussed in a separated issue, as the point of this PR is to fix gazebosim/gz-sim#1116 with minimal modifications.

[codecov]

Codecov Report

Merging #661 (52b0b59) into ign-rendering6 (d773877) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@                Coverage Diff                 @@
##           ign-rendering6     #661      +/-   ##
==================================================
- Coverage           54.95%   54.93%   -0.02%     
==================================================
  Files                 202      202              
  Lines               21102    21102              
==================================================
- Hits                11596    11592       -4     
- Misses               9506     9510       +4     

Impacted Files	Coverage Δ
ogre2/src/Ogre2RenderTarget.cc	85.68% <100.00%> (-0.96%)	⬇️

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[traversaro]

FYI @srmainwaring as you recently modified this code in #470 .

[iche033]

looks good to me, thanks for the fix.

[srmainwaring]

as you recently modified this code in #470 .

@traversaro thanks! Checked this on an Ubuntu 22.04 VM (VMware Fusion) and running fine under llvmpipe (LLVM 13.0.1).