CG: Packing 3 floats into 1 for shaders

// Modification of Cameron.'s code from http://forum.unity3d.com/threads/can-i-send-data-as-w-via-vertex-data.114111/#post-769621
// by Alex May 2015

// Packs a normalised direction vector into a single float
float PackVector3(Vector3 vector3)
{
    // Scale  Bias values to 8 bit bytes in range of 0 to 255
    int x = PackFloat(vector3.x);
    int y = PackFloat(vector3.y);
    int z = PackFloat(vector3.z);

    uint  packedByte  = (uint)((x << 20) | (y << 10) | z);
    float packedFloat = (float)((double)packedByte / (double)(1<<30));

    return packedFloat;
}

// UnPack normal from float
Vector3 UnPackVector3(float src)
{
    Vector3 output = Vector3.zero;

    // Unpack to 0...1 range
    output.x = Frac(src);
    output.y = Frac(src * 1024.0f);
    output.z = Frac(src * 1048576.0f);

    // Bias to -1..1 range
    output = (output * 2f) - Vector3.one;

    return output;
}



void TestPackVector3(Vector3 normal)
{
    normal.Normalize();

    float f = PackVector3(normal);
    Vector3 result = UnPackVector3(f).normalized;
    Vector3 error  = normal - result;

    string s = "";

    s += "Testing: (" + normal.x + ", " + normal.y + ", " + normal.z + ")\n";
    s += "Result : (" + result.x + ", " + result.y + ", " + result.z + ")\n";
    s += "Error  : (" + error.x  + ", " + error.y  + ", " + error.z  + ")\n";

    Debug.Log(s);
}


// Helper method that converts a float in the
// range(-1..1) to a 10 bit int in range(0..1023)
int PackFloat(float x)
{
    x = (x + 1.0f) * 0.5f;   // Bias

    return (int)(x*1023.0f); // Scale
}


// Helper method to emulate CG's frac(x)
float Frac(float x)
{
    return x - Mathf.Floor(x);
}


/* Cg code for your shader

inline float3 UnPackVector3(float src) {
    return (frac(float3(1.0f, 1024.0f, 1048576.0f) * src) * 2) - 1;
}

*/