wow , tanks a lot MasterQ32 !

We don't see the effect a lot, i think it's because of blue background and textures you used ; i'll gonna try it right now

That's strange your code takls about terrain and lights ?
And where do i put the shader code ?

Arrrghhhhh .... The day 3DGS will evolve a bit more instead of beeing so prehistoric, and allow direct integration of shader code without coding , drag and drop and menu select for shaders ....
One of the many reasons it is hard for 3D artists to go for 3DGS.