- Mob Cap of 15 passive creatures in a 17x17 area (unlimited height... not quite a chunk but slightly larger)
- Blocks they spawn on must be grass blocks, with light level 9 or higher (fully open to the sky is fine, or lit with torches/glowstone/jack o'lanterns should work too)
- With multiple eligible blocks, the "highest" block in a column of blocks gets preference for spawning
- No player can be within 24 blocks of the block
- Passive mobs only spawn every 20 seconds (or an attempt happens about every 20 seconds)
- Can't be a desert, beach, river, and ocean biomes
- Must have at least two air blocks above grass blocks
- Be in the overworld (where you start to play vanilla Minecraft)
I'm trying to set up a passive mob spawning area but it seems to me that even if following all of these spawning rules, I'm still having problems getting passive mobs to spawn. Where I'm especially suspect is that the 24 block distance for having passive mobs spawn is something I don't think is happening. While hostile mobs will certainly spawn in a 24+ block distance (meeting their rules for spawning) I think it may be a fair bit further. Having the grass blocks much further away doesn't seem to have an impact either, so I think you must be at some distance between 24 and about 100 blocks away for them to spawn.
I don't know what the specific distance range is for this to happen is at, and digging through the Minecraft source code (through MCP) doesn't seem to help for me either. In these survival type maps, you are limited on how much dirt you have available, so getting the specific distances is a bit important, where you can hang out and do crafting, mining cobblestone with a lava+water generator, or collecting stuff from a hostile mob farm. I know that you can spawn passive mobs in these kind of maps or situations, I'm just trying to nail down what other conditions might be needed for getting these kind of very useful creatures to spawn for players in survival mode.
Any help to solve this "problem" would be useful.