I have succesfully created a GLSL shader for a billboarding effect. I want to tweak this to restrict the billboarding to an arbitrary axis, i.e. a billboarded quad only rotates itself about the y-axis. I use the y-axis as an example, but essentially I would like this to be an arbitrary axis. Can anyone show me how to modify my existing shader below, or if I need to start from scratch, point me towards some resources that could be helpful?

precision mediump float; 

uniform mat4 u_modelViewProjectionMat;      
uniform mat4 u_modelMat;               
uniform mat4 u_viewTransposeMat;   

uniform vec3 u_axis; // <------------ !!! the arbitrary axis to restrict rotation around

attribute vec3 a_position0;     
attribute vec2 a_texCoord0;     

varying vec2 v_texCoord0;      

void main()
{
    vec3 pos = (a_position0.x * u_viewTransposeMat[0] + a_position0.y * u_viewTransposeMat[1]).xyz;
    vec4 position = vec4(pos, 1.0);

    v_texCoord0 = a_texCoord0;

    gl_Position = u_modelViewProjectionMat *  position;
}