I have a program where I draw the movements of an item in 3 dimensions. This can be a submarine, car of airplane.
I would like to draw the sea surface all over my scene. I mean kind of a square all over the place where z=0. How can I do this?
I’m not entirely sure if I get what you mean, but from the sound of it, you probably only need to draw a huge QUAD the color of the water over the dimensions of your world. OpenGL will crop and cull as needed.
If you need to blend it, or texture it, you should be able to figure that out on your own.