mapfix

Fix some map errors (flow and light problems)

Look at the water and the jungle trunk at the center.

minetest.conf settings

• mapfix_default_size (by default 40) : size used when omitted
• mapfix_max_size (by default 50) : maximum size allowed for players
• mapfix_delay (by default 15) : minimal delay in seconds between 2 "/mapfix" (to avoid server freezing)