[Metal] update custom_shaders_uniforms example

[srmainwaring]

This PR adds metal shaders to the custom_shaders_uniforms example.

🎉 New feature

Enhances #520

Summary

• Metal vertex and fragment shaders are added to the custom_shaders_uniforms example.
• Ogre2Material is modified to specify the render system being used when creating the GPU programs.
• Add an accessor for the graphics API to Ogre2RenderEngine

Test it

Run the example using ogre2 and specifying metal as the graphics API:

./custom_shaders_uniforms ogre2 metal

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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

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.

[srmainwaring]

@iche033 this PR is an intermediate step to getting the waves example working as it doesn't depend on textures.

Main design input I'd like is the best way to select the graphics API being used in Ogre2Material.cpp.

[codecov]

Codecov Report

Merging #554 (ed6f256) into main (1e711f6) will decrease coverage by 0.04%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #554      +/-   ##
==========================================
- Coverage   53.18%   53.14%   -0.05%     
==========================================
  Files         213      213              
  Lines       21200    21216      +16     
==========================================
  Hits        11276    11276              
- Misses       9924     9940      +16     

Impacted Files	Coverage Δ
...lude/ignition/rendering/ogre2/Ogre2RenderEngine.hh	100.00% <ø> (ø)
ogre2/src/Ogre2Material.cc	64.06% <0.00%> (-1.68%)	⬇️
ogre2/src/Ogre2RenderEngine.cc	78.36% <0.00%> (-0.35%)	⬇️

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[iche033]

Main design input I'd like is the best way to select the graphics API being used in Ogre2Material.cpp.

how about adding an accessor function to get the graphicsAPI var from Ogre2RenderEngine?

[srmainwaring]

how about adding an accessor function to get the graphicsAPI var from Ogre2RenderEngine?

Yes that works for me, the variable is already available in the private data. I'll have to check if Ogre2Material has access to the render engine as well.

[iche033]

I think you should be able to get the engine by doing:

auto engine = Ogre2RenderEngine::Instance();

[iche033]

There is a compile error in CI due to conflict between enum and function name. This fixes the issue for me:

patch

diff --git a/ogre2/include/ignition/rendering/ogre2/Ogre2RenderEngine.hh b/ogre2/include/ignition/rendering/ogre2/Ogre2RenderEngine.hh
index c1ee131b..a1a69867 100644
--- a/ogre2/include/ignition/rendering/ogre2/Ogre2RenderEngine.hh
+++ b/ogre2/include/ignition/rendering/ogre2/Ogre2RenderEngine.hh
@@ -216,7 +216,7 @@ namespace ignition
 
       /// \brief Get the render engine's graphics API
       /// \return The graphics API enum class
-      public: GraphicsAPI GraphicsAPI() const;
+      public: rendering::GraphicsAPI GraphicsAPI() const;
 
       /// \brief Pointer to the ogre's overlay system
       private: Ogre::v1::OverlaySystem *ogreOverlaySystem = nullptr;

[srmainwaring]

Updated.

[iche033]

looks good to me!