Hey thanks a lot and cool that it already works :)

I think we need to design this a bit more to make it more in line in the way that it is supposed to be used, i.e. by putting these snippets as files somewhere and merging the shader code better.

I'll think about it and will come back to you with more ideas.

Okay, I finally have time to respond here :D As said before, I like the direction where this is going, but I have a few requests for how commands should be integrated.

1. If shader source code is supposed to be templated, I don't think it should be loaded as ShaderSource at the start as the code may be incomplete. Instead, there should probably be a ShaderTemplate class that the template is loaded into which can be fed with ShaderSnippets to insert into placeholder in the template. Once ShaderTemplate is configured with snippets, it should be able to create the final source code which can then be passed to the ShaderSource constructor. This additional layer would probably prevent a lot of problems for templates that are not properly initialized.
2. I think we can already make the feature more versatile and extendable by not having a generic INSERT_POINT in the shader source code and instead assigning placeholder IDs. Multiple shader snippets could then be inserted into different position in the shader template based on their ID.
3. I don't think the logic for creating shader code should be hardcoded, e.g. in WorldShaderCommands, because it defeats the point of making the commands configurable. The command code should be loadable from a file that the user can create. If we have to recompile the engine every time you want to change the commands, we might ass well just use the current solution.
4. It's probably better to create a renderer demo for this feature rather than using it in the actual renderer. This way, we can test the design and change it without having to worry about it affecting the main rendering loop just yet.