Struggling with billboarded quads

[stiff tide]

I am trying to render quads that always face the camera. I currently extract the rotation part of the 4x4 view matrix like this:

glm::mat3 rotationOnly = viewonly;
                    
QuadParticleData quadData{
    .viewProj = viewproj,
    .billboard = glm::transpose(rotationOnly)
};

Then, in the shader, I take the quad point (a vec2), scale it, apply the bilboard matrix, and finally apply the billboard matrix:

 vec3 localPoint = vec3(inVertex * data.scale, 0);
localPoint = matrices.billboard * localPoint;

vec4 vert = vec4(localPoint + data.pos, 1);

vert = matrices.viewProj * vert;

However, the quads do not face the camera. If I remove the bilboard operation, then the quads are aligned to the XY axes. How can I fix my math so that the billboarding works?

[sleek wren]

I remember struggling with this too and in fact I just do my particles in screen space

Or rather view space

I transform the center of the particle into view space with the mv matrix and then simply construct the quad vertices there

And then project the result

Much easier than trying to transform some fake world-space mesh that doesn't actually exist in the first place

[stiff tide]

I decided to try this:

const vec3 centerInViewSpace = (matrices.view * vec4(data.pos,1)).xyz;

const vec3 offsetPoint = vec3(inVertex * data.scale, 0);

vec4 vert = vec4(centerInViewSpace + offsetPoint,1);

vert = matrices.proj * vert;

However, it appears that the particles are ending up behind the camera
inVertex is a vec2 with (-1,-1),{-1,1),(1,1),(1,-1) as possible values