I have taken a look at BlockStairs.java, but I'm not sure I understand what's going on. Basically I just want to change a neighboring block based on the direction and position of the just-placed block. I don't know what I should use to do this (neighborChanged method?) so a point in the right direction would be appreciated. Thanks.

Override neighborChanged and modify the blockstate based on the neighbor blockstate, and then go in your blockstate JSON (in your assets) and add a model for the state you made.

1 hour ago, hiotewdew said:

Override neighborChanged and modify the blockstate based on the neighbor blockstate, and then go in your blockstate JSON (in your assets) and add a model for the state you made.

Thanks, this is what I was looking for. Is there an example of how I should modify the blockstate in the neighborChanged method?

20 hours ago, Siqhter said:

Thanks, this is what I was looking for. Is there an example of how I should modify the blockstate in the neighborChanged method?

Try looking at getStateForPlacement in BlockStairs. It gets the neighbor's blockstate and then uses withProperty to adjust the current one to match the others.

Thanks, I think I breezed over that but I'll take a closer look at it now.