fix cave mode for caves below 0 (#276)
fix cave mode for caves below 0 (#276)

... as they where not shown before.
Also the depth gradient was not working at exactly depth -1.

Rest of the changes is just naming refactor and slight performance improvement due to getting code out of the main render loop.
mrkite/minutor,EtlamGit/minutor,mrkite/minutor,EtlamGit/minutor,EtlamGit/minutor,EtlamGit/minutor,mrkite/minutor,mrkite/minutor,mrkite/minutor,EtlamGit/minutor