//
// subroutine call example
//
// vertex shader with per-vertex diffuse lighting for a 4 directional
//   lights + ambient
//
// written assuming that the lightcolor has been premultiplied by the
// diffuse coefficient and that the ambientcolor has been premultiplied
// by the ambient coefficient

struct appdata {
    float4 position : POSITION;
    float3 normal   : NORMAL;
    float4 color    : COLOR0;
};

struct v2f {
    float4 HPOS : POSITION;
    float4 COL0 : COLOR0;
};

float3 diffuse(float3 normal, float3 lightv, float3 color)
{
    return max(dot(normal, lightv), 0) * color;
}

v2f main(appdata I,
         uniform float3x3 object_matrix,
         uniform float4x4 objviewproj_matrix,
         uniform float3 lightdir[4],
         uniform float3 lightcolor[4],
         uniform float3 ambientcolor)
{
    v2f O;
    float3 norm;

    // transform vertices into projection space using the pre-multiplied matrix
    O.HPOS = mul(objviewproj_matrix, I.position);

    norm = mul(object_matrix, I.normal); // transform normal to world space

    O.COL0.rgb = I.color.rgb *
        diffuse(norm, lightdir[0], lightcolor[0]) *
        diffuse(norm, lightdir[1], lightcolor[1]) *
        diffuse(norm, lightdir[2], lightcolor[2]) *
        diffuse(norm, lightdir[3], lightcolor[3]) + ambientcolor;
    O.COL0.a = I.color.a;

    return O;
} // main

