how do i skip spawn if alpha of a position map is zero?

[laurentlavigne]

I create a position map by shooting rays down to the world and setting x,y,z in a texture map’s r,g,b
if the raycast hits nothing i set the alpha to zero
how do i skip a spawn if the alpha is zero?
to avoid this

here is the graph

[JulienF_Unity]

Hi, you can use the alive attribute in Init context to reject the particle. Setting alive attribute to false, depending on contexts, means:

• In Init: discard particle and don’t spawn it
• In Update: kill particle
• In Output: cull particle (particle is not visible but still alive)

[laurentlavigne]

How do I get the alpha from a texture object? There is no split channel operator
let me rephrase:
how do i get an alpha from this node

which is what that block reads

without having to use that node

which requires me to compute uv from index (trying to avoid that as it’s super costly in mods and divs… and also doesn’t work for me)