Thx for your reply
For vertex visibility you need to render again outputted vertices (maybe as points?) and check if Z test pass/fail or use occlusion query. If you want indices of those vertices you just have to add a vertex attribute that store the index
- how can I perform this Z test and/or occlusion query?
- should I use GL_PASS_THROUGH_TOKEN to assign index or there is other/better way?