Migrating OpenSceneGraph master to MeshShaders branch

[robertosfield]

One of my plans for the future OpenSceneGraph-3.8 release is to use the MeshShaders branch as a base rather than master branch. I want to do this because after the 3.6.5 maintenance release I merged merge my 3/4's completed experimental shader_pipeline work into master, but this now realize was a serious mistake.

Reality is I will never complete this experimental work, I neither have the time and technically now feel trying to solve integration of OpenGL fixed function pipeline with shaders has little point - the future is shaders. This mistake in merging a large block of experiment work left OpenSceneGraph master is a dangling, difficult to support state. I am now trying to navigate a way of creating a new master that doesn't contain this shader_pipeline work.

The steps I have taken so far:

1. Created a Deprecated_master_20th_November_2022 branch to capture the state of master with the problem merges. This will give us a reference point for any code/functionality that we might loose in moving to a new master so we can pull it into the new master.
2. Created a new_master branch (originally named Experimental_master) that essentially resets master to the current state of the MeshShaders branch. The MeshShaders branch is essentially OpenSceneGraph-3.6 with the OpenGL MultiView and OpenGL MeshShader extension supported added.

My next steps will be:

3. Reviewing the differences between master and the new_master to see what elements in the current master are suitable with merging into the new_master. The difference between the two can be see with this github comparisons across branches.
4. Call for input from the community about what elements from master they'd like to see migrated into the new_master.
5. Merge useful parts from current master into new_master.
6. Create a PR for the Experimental_master, and call for feedback.
7. Merge the PR so that master now becomes the basis for ongoing work without any of the shader_pipeline and other experimental work.
8. Work through the Issues and PRs from the community, with such a big set of changes to master due to step 7 I am expecting a few PRs to break, or perhaps not be appropriate anymore. Where required these will need to be modified, or abandoned.

With all this work I am trying to get the OpenSceneGraph back into a place where we can move forward and get new stable releases out. My guideline for all this is to maintain stability and ease of maintenance for a body of software that is now focused on maintaining a stable and reliable base, whilst minimizing the burden on myself and members of the community to keep things working as hardware, OS's and software stacks evolve over the coming years.

Thanks in advance with your help during this transition.
Robert.

[robertosfield]

This afternoon I merged the @mxgrey's modernize_cmake work that I previous merged with OSG master, I could easily get git/github to do this against the Experimental_master branch so it was a bit more manual a merge than I would have liked, hence why it took so long. The changes are: b628f53

Not all merging of functionality that is only presently in master into the what will be the new master shouldn't be this difficult, so I'm hoping this task won't break me. I don't want to leave the old master in place for too long though as folks will be checking out the old master and basing their work on it, only for me to go change the rug from underneath them. Doing it sooner will mean only merging a small number of changes in OSG master than weren't in the MeshShaders/3.6 branch that I have used with the Experimental_master.

The name of the Experimental_master branch made sense for my initial experiments but now that is evolving towards something suitable to make the new master I will probably renamed it so something more suitable.