A shader library right in the playground source -- you can replace these shaders to experiment more!

shaders.swift

// create a shader library in source (not precompiled)
let runtimeLibrary = try device?.makeLibrary(source: """
    #include <metal_stdlib>
    using namespace metal;
	
    vertex float4 copy_vertex(
        const device packed_float3* vertex_array [[buffer(0)]],
                                 unsigned int vid [[vertex_id]]) {
        return float4(vertex_array[vid], 1.0);
    }
	
    fragment half4 constant_color() {
        return half4(0.75,0.95,0.35,1.0);
    }
""", options: nil)