I am learning vertex animation textures. Already used UV.x as normalised vertex index to animate a flag and it works great. 

[![enter image description here][1]][1]

I don't have access to uv2 ("game" engine still under in dev stage) but I want to apply textures. I found a [technique][2] for packing float32 in [0,1) range into a texture (in my case vertex color) so I can free my uv space. Here is my code :

```python
# Blender side. Not sure if 255.0 is correct shift, in some sources i found 256.0

def frac(x):
    return x - np.floor(x)

def pack_float32_to_vec4(v):
    enc = np.float32((1.0, 255.0, 65025.0, 16581375.0)) * v
    enc = frac(enc)
    enc -= (enc[1], enc[2], enc[3], enc[3]) * np.float32((1.0/255.0, 1.0/255.0, 1.0/255.0, 0.0))
    return enc


def write_vertex_ind_to_vertex_color(me, image_size):
    if (len(me.vertex_colors) <= 0 ) :
        me.vertex_colors.new()

    v_col = me.vertex_colors.active.data
    uv_layer = me.uv_layers[0]
    
    for loop in me.loops:
        data = (loop.vertex_index + 0.5) / image_size
        color = pack_float32_to_vec4(data)
        v_col[loop.index].color = color

        uv_layer.data[loop.index].uv = (
            (loop.vertex_index + 0.5) / image_size, 128/255 
        )

```
And in shader I try to unpack :
```glsl
// shader side, again I am not sure on 255 here
float unpackFloatFromVec4(const vec4 value) {
  vec4 bitSh =  vec4(1.0, 1.0 / 255.0, 1.0 / 65025.0, 1.0 /  16581375.0);
  return dot(value, bitSh);
}
```

Here is the difference for UV.x and my unpacked value : 

``` glsl
float u = unpackFloatFromVec4(vCol);
Color = abs((uv.x - u)).xxx1;

```


[![uv.x vs unpacked][3]][3]

Vertex color seems to have sRGB correction, which I've tried to fix in python and shader by pow(1.0 / 2.2), but with no luck. It feels like I loose some precision.

``` glsl
vCol = vec4(pow(vCol.xyz, vec3(1.0 / 2.2)) , vCol.w);
float u = unpackFloatFromVec4(vCol);
Color = abs( (uv.x - u) * 100.0).xxx1; # mul 100.0 to see difference

```
[![uv.x vs unpacked \w gamma correction][4]][4]

So the even this difference is enough to sample the wrong texel: 

[![just garbage][5]][5]

 I use glTF file format for the model. 


  [1]: https://i.sstatic.net/IHLbIm.png
  [2]: http://marcodiiga.github.io/encoding-normalized-floats-to-rgba8-vectors
  [3]: https://i.sstatic.net/UIZD1m.png
  [4]: https://i.sstatic.net/0cbOqm.png
  [5]: https://i.sstatic.net/wlchEm.png