// vertex shader with per-vertex diffuse lighting for a single directional
//   light + 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 : ATTRIB0;
    float3 normal : ATTRIB1;
    float4 color : ATTRIB2;
};

struct vf20 {
    float4      HPOS : POSITION;
    float4      COL0 : COLOR0;
    float4      TEX0 : TEXCOORD0;
};

vf20 main(appdata I,
          uniform float3x3 object_matrix,
          uniform float4x4 objviewproj_matrix,
          uniform float3 lightdir,
          uniform float3 lightcolor,
          uniform float3 ambientcolor)
{
    vf20 O;
    float diffuse;

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

    // transform the normal to world space, use the dot product to
    // calculate the diffuse intensity, if facing away from the light
    // make it 0

    diffuse = max(0, dot(mul(object_matrix, I.normal), lightdir));

    O.COL0.rgb = I.color.rgb * diffuse * lightcolor + ambientcolor;
    O.COL0.a = I.color.a;

    return O;
} // main