Dockerhub Automated Build With Git Commit Hash

I have search and try this before i ask in this forum.
I have setup my private registry on Dockerhub, and use Build image on Dockerhub Infrastructure.
For static git branch , it is working perfectly.

But the documentation is really confusing for build an image based on git commit hash.
I know that there is build “Environment variables for building and testing”
but how to use it on Dockerhub?

My case is i want to build every commit on git branch and using git commit hash as my image tag.
Please advice

Thank You

no need to answer it guys
its solved

How did you do this?