Compute normal based on Voronoi pattern - opengl

Question

I am applying a 3D Voronoi pattern on a mesh. Using those loops, I am able to compute the cell position, an id and the distance.
But I would like to compute a normal based on the generated pattern.
How can I generate a normal or reorient the current normal based on this pattern and associated cells ?
The aim is to provide a faced look for the mesh. Each cell's normal should point in the same direction and adjacent cells point in different directions. Those directions should be based on the original mesh normals, I don't want to totally break mesh normals and have those points in random directions.
Here's how I generate the Voronoi pattern.
float3 p = floor(position);
float3 f = frac(position);
float id = 0.0;
float distance = 10.0;
for (int k = -1; k <= 1; k++)
{
for (int j = -1; j <= 1; j++)
{
for (int i = -1; i <= 1; i++)
{
float3 cell = float3(float(i), float(j), float(k));
float3 random = hash3(p + cell);
float3 r = cell - f + random * angleOffset;
float d = dot(r, r);
if (d < distance)
{
id = random;
distance = d;
cellPosition = cell + p;
normal = ?
}
}
}
}
And here's the hash function :
float3 hash3(float3 x)
{
x = float3(dot(x, float3(127.1, 311.7, 74.7)),
dot(x, float3(269.5, 183.3, 246.1)),
dot(x, float3(113.5, 271.9, 124.6)));
return frac(sin(x)*43758.5453123);
}

Answer 1

This looks like a fairly expensive fragment shader, it might more sense to bake out a normal map than to try to do this in real time.
It's hard to tell what your shader is doing but I think it's checking every pixel against a 3x3 grid of voronoi cells. One weird thing is that random is a vec3 that somehow gets assigned to id, which is just a scalar.
Anyway, it sounds like you would like to perturb the mesh-supplied normal by a random vector, but you'd like all pixels corresponding to a particular voronoi cell to be perturbed in the same way.
Since you already have a variable called random which presumably represents a random value generated deterministically as a function of the voronoi cell, you could just use that. For example, the following would perturb the normal by a small amount:
normal = normalize(meshNormal + 0.2 * normalize(random));
If you want to give more weight to the random component, just increase the 0.2 constant.