Vertex Animation Textures

Prerequisites

• Normals
• UVs

Create orient attribute (allows us to update normals in the vertex shader)

• Create normal (N) attribute if missing
• Create tangentu attribute (preferably MikkT)
• Create matrix3 from N and tangentu
• Convert matrix3 to orient attribute (quaternion)

N = normalize(N);
vector tangentu = length(tangentu) > 0.01 ? normalize(tangentu) : {1, 0, 0};

matrix3 m = maketransform(normalize(cross(tangentu, N)), N);
quaternion orient = normalize(quaternion(m));

Calculate position delta

• For each point calculate the vector delta from the first frame to the current frame.

vector delta = P_current_frame[i] - P_first_frame[i]

• If no colour exists add a default vertex colour of 1,1,1

Create a copy of the geometry for every frame in the animation.

• This is just a way to access attributes for each frame when generating the texture. This could also be done as a loop when writing the values to the texture.
• It can also help with the next step of the process.

Calculate the min and max bounds for the entire animation.

Mesh Preparation

• Scale to match target platform (x100)
• Triangulate mesh (more consistent that trusting the target platform)
• Create uv2
  • Get max texture width (eg. 1024)
  • Get total frame count (end frame - start frame + 1)

  float max_width = 1024;
  float numpt = (total number of points); 
  float frame_count = 100;
  
  float width = min(max_width, numpt);
  float rows = ceil(numpt / max_width);
  
  float unit_size = 1.0 / width;
  float unit_size_y = 1.0 / rows / frame_count;
  
  float i = (float)point_index;
  
  uv2.x = (0.5 + i - floor(i / width ) * width) * unit_size;
  
  uv2.y = 1.0 - (floor(i / width) * unit_size_y) - 0.5 * unit_size_y;

• Add two triangles to the mesh. One at the min and one at the max bound value.
  • This helps us normalize value when exporting the texture, and then expanding them back to world space in the shader.
  • You might be tempted to add a single vertex but this can be problematic with some platforms that will automatically cull vertices that aren't associated with a triangle.
• Add tangentv attribute to geometry

vector tangentv = cross(N, tangentu);
vector tangentv = normalize(tangentv);

if ("binormal_mode" == 1) {
  tangentv *= -1.0;
}

• Export mesh as gltf/fbx

Generate position texture

• Dimensions = x: number of points in geo, y: number of frames in anim
• For each pixel in x get the P value of the corresponding point and for each pixel in y get the frames P value.

for x in texture_width:
  for y in total_frames:
    return getP_atFrame(x,y)
    //x is P index
    //y is Frame index

• You might need to swap components or flip coords depending on the handedness of the 3D software and the target platform.
  • eg. swap y with z, negate x
• Set alpha to 1 (white). Some platforms will premultiply alpha regardless of settings.
  • You could also use alpha to store pscale.

Generate orient texture

• Same approach as position texture except swapping and flipping the quaternion components can be a bit tricky.