THREE.js - Billboard Vertex Shader

Question

I have the need to orientate an instance of THREE.Mesh to always face the camera. I know I could just use the [THREE.Mesh].lookAt() method, but I'm trying to work on my GLSL chops a bit more and want to be able to do this in a vertex shader.

I've read through NeHe's Billboarding tutorial, and it makes sense to me. Well, all apart from the bit where one applies these orientation vectors to each vertex.

I feel like I'm very close to getting this working, but as it stands at the moment, my vertex shader is looking more like a 90s rave video than a billboard:

Progress so far fiddle: http://jsfiddle.net/RZ4XE/2/

Below is my vertex shader (the fragment shader just assigns a vec4 color). It's making use of various default uniforms / attributes that THREE.js provides, listed below just in case someone unfamiliar with THREE.js is reading this :)

• cameraPosition (vec3),
• position (vertex position, another vec3),
• projectionMatrix (camera's projectionMatrix, mat4),

• modelViewMatrix (camera.matrixWorldInverse * object.matrixWorld, mat4)

  void main() {
  
      vec3 look = normalize( cameraPosition - position );
  
      if( length( look ) == 0.0 ) {
          look.z = 1.0;
      }
  
      vec3 up = vec3( 0.0, 1.0, 0.0 );
      vec3 right = normalize( cross( up, look ) );
      up = normalize( cross( look, right ) );
  
  
      mat4 transformMatrix;
  
      transformMatrix[0][0] = right.x;
      transformMatrix[0][1] = right.y;
      transformMatrix[0][2] = right.z;
  
      transformMatrix[1][0] = up.x;
      transformMatrix[1][1] = up.y;
      transformMatrix[1][2] = up.z;
  
      transformMatrix[2][0] = look.x;
      transformMatrix[2][1] = look.y;
      transformMatrix[2][2] = look.z;
  
      gl_Position = projectionMatrix * modelViewMatrix * transformMatrix * vec4( position, 1.0 );
  }
  

Thanks in advance.

Answer 1

Apparently this works:

gl_Position = projectionMatrix * (modelViewMatrix * vec4(0.0, 0.0, 0.0, 1.0) + vec4(position.x, position.y, 0.0, 0.0));

I'm actually trying to figure out how to do axis aligned billboards.