[Citadel] Update tutorials

[claireyywang]

• Use Doxygen code snippet and image
• Add example code
• Update tutorial titles and content

Will forward port this to Dome and main if approved.

[claireyywang]

@chapulina I addressed your tutorial comments in this PR. Feel free to take a look if you have time .

[codecov]

Codecov Report

Merging #204 (ac86f6f) into ign-physics2 (671ee8c) will increase coverage by 0.19%.
The diff coverage is n/a.

❗ Current head ac86f6f differs from pull request most recent head 5add03c. Consider uploading reports for the commit 5add03c to get more accurate results

@@               Coverage Diff                @@
##           ign-physics2     #204      +/-   ##
================================================
+ Coverage         82.94%   83.14%   +0.19%     
================================================
  Files               106      106              
  Lines              4034     3998      -36     
================================================
- Hits               3346     3324      -22     
+ Misses              688      674      -14     

Impacted Files	Coverage Δ
tpe/lib/src/Model.cc	98.36% <0.00%> (-0.03%)	⬇️
tpe/lib/src/Link.cc	100.00% <0.00%> (ø)
tpe/lib/src/Link.hh	100.00% <0.00%> (ø)
tpe/lib/src/World.cc	100.00% <0.00%> (ø)
tpe/plugin/src/SDFFeatures.cc	84.45% <0.00%> (+1.12%)	⬆️
tpe/plugin/src/FreeGroupFeatures.cc	79.68% <0.00%> (+12.58%)	⬆️

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[chapulina]

Can we add a CMakeLists file to examples/simple_tpe_plugin so that it's possible to compile it?

[claireyywang]

Can we add a CMakeLists file to examples/simple_tpe_plugin so that it's possible to compile it?

I added an example CMakeList but don't think it's working correctly yet. I'm still not sure how exactly CMake links different libraries so it'd take some time to figure that out. I think it'd be preferable to merge the tutorial part of the this PR first, and take the CMake part out for later improvement. What do you think?

[chapulina]

I added an example CMakeList but don't think it's working correctly yet.

The plugin fails to compile for me with:

/home/chapulina/ws_citadel/src/ign-physics/examples/simple_tpe_plugin/plugin.cc:20:10: fatal error: Base.hh: No such file or directory
 #include "Base.hh"
          ^~~~~~~~~

Looking through the code, I imagine this is supposed to refer to tpe/plugin/src/Base.hh, right? The reason that the example is not being able to find it, is that the header isn't being installed. I suspect this is on purpose though, because we don't need downstream users to be using tpe-plugin, only tpe-lib, right? I haven't looked closely enough to have a suggestion here, but I think that the example needs to be reworked to only use things from tpe-lib, not tpe-plugin.

I think it'd be preferable to merge the tutorial part of the this PR first, and take the CMake part out for later improvement.

I think that the CMake failure exposed a potential problem in the tutorial. I think it's worth it getting it to work before we publish it, so we're sure we're giving users working instructions.

[chapulina]

I pushed some tweaks to:

• Make the example and test compile
• Maintain the current tutorial URLs, so we don't break existing links to the site
• Fix snippets

LGTM!