Where can I find a full shader example with map_vertex and map_frag_data?

[Boscop]

1. Where can I find a full shader example with map_vertex and map_frag_data?

2. And how to write fragment depth?

3. Apart from these special functions and imports, does cheddar support everything that GLSL does? I'm asking because here you wrote:

   We need more built-ins, such as PI, PI_2, etc.

[Boscop]

4. If at some time you come to the realization that you also need the position information in the result, you just have to change the above code to:

   
   struct Vertex {
   vec4 chdr_Position;
   vec3 position;
   vec4 color;
   };

Vertex map_vertex(vec3 position, vec4 color) { return Vertex(vec4(position, 1.), position, color); }

Why can't I just use `chdr_Position` in my fragment shader? Why do I have to add another `position` field?