I – Unity Limits (Yes I finally reached some)<\/h3>\n
I use Unity to create my game and (luckily?), Unity provides 2 functions to load a new level “in the background” so that you don’t notice any lag:<\/p>\n
- \n
- LoadLevelAsync<\/b>: loads a new level in background. Once loaded, the new level replaces the current one.<\/li>\n
- LoadLevelAdditiveAsync<\/b>: Same thing, but adds the content of the new level to the current one. This is obviously what I’m going for here.<\/li>\n<\/ul>\n
But this is theoretical only. Unity is a great software, but some points are still under heavy development. These ones are. And it impacts the game in a way I didn’t think about: after using LoadLevelAdditiveAsync, all the IA agents of the new level crash.<\/p>\n
This occurs because the IA uses a “NavMesh<\/b>” (= Navigation Mesh) to represent the walkable areas in the level. The IA can only walk\/move\/search a path on the NavMesh. Problem is, Unity only authorizes 1 NavMesh to be loaded in memory at a time, and you can’t load a NavMesh using LoadLevelAdditiveAsync. Technical limitation. I can’t argue.<\/p>\n
![\"\"](\"http:\/\/3.bp.blogspot.com\/-SIXRJn8i_CM\/UwZp6vAIGRI\/AAAAAAAAHo4\/VyCYYkHfB1U\/s1600\/20140220_navMesh.jpg\")
<\/a><\/div>\nThe NavMesh: enemies can only walk on the blue zone. The computation of this 3D NavMesh is a quite complex task… <\/i><\/div>\n<\/p>\n
II – Time for Hacks<\/h3>\n
I found a hack on a forum post<\/a> : using LoadLevelAsync (which actually loads the new NavMesh in memory) and tagging all objects of the current level not to be destroyed (a cool feature I discovered while reading the forums. Great community by the way).
\nThis is supposed to do the trick but it rises 2 more problems:<\/p>\n- \n
- LoadLevelAsync is not actually a background task. It really freezes the game for a few ms, and it IS visible.<\/li>\n
- Cool, the NavMesh of the new level is OK, and the IA too, but what happens if I go back towards the 1st level (which is still visible but with no corresponding NavMesh and no IA)? If I wan’t to reload only the NavMesh of the 1st level… I can’t without reloading the whole level, which may result in objects flickering during the reload.<\/li>\n<\/ul>\n
At this point, I’m faced with Unity bugs I can’t fix and I’m left with a few options:<\/p>\n
- \n
- Wait for a bug fix<\/b> from Unity about the NavMesh+LoadLevelAdditiveAsync problem. I don’t think it will come before I release my game, the Unity guys have loads to do and this is not a priority.<\/li>\n
- Use a 3rd-party library<\/b>. I must find one that does NavMesh generation and path-finding, is real-time, and dynamically loads levels.<\/li>\n
- Recode everything<\/b> that is not working. Not impossible (I already coded a real-time A* path-finding algorithm for World of Ninjas<\/a>, but it works only on a 2D grid)… but hardly realistic. Good guys spent months developping systems much more reliable than anything I could do in a few weeks.<\/li>\n
- Find another workaround<\/b>. I didn’t find any when I spent a few hours on forums and faqs.<\/li>\n
- Give up<\/b>. This is a serious option. I can perform the navigation part on a 2D map where you click where you wan’t to go. All islands would be accessible too, and it won’t change the gameplay on each island. Maybe I’ll even consider that if I achieve to create\u00a0 a “real” open world but it’s not fun to explore.<\/li>\n<\/ul>\n
But before giving up I heard a lot of good things about a 3rd-party library implementing the classical A* path-finding algorithm: Aron Granberg A* path-finding library.<\/p>\n
<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n![\"\"](\"http:\/\/2.bp.blogspot.com\/-ICg8nAOpF14\/UwZs5dTiPrI\/AAAAAAAAHpI\/kpNqbHCg_gs\/s1600\/20140213_172417.png\")
<\/a><\/div>\n\u00a0Lots of levels loaded together!<\/i><\/div>\n<\/p>\n
III – A new lib: A*<\/h3>\n
Cool! A new library full of promises. But before commiting to this, I have to test that every basic IA feature already provided by Unity is implemented in this library.<\/p>\n
I start with the free version of the library, which means… there is no NavMesh generation available (only on the full 100$ version). Of course, I can buy the full version, but I’m not sure this library solves my “dynamic loading” problem. I must first test it on this specific point.<\/p>\n
I know that Unity can generate NavMeshes<\/b> (I used them before). So I write a script to convert Unity NavMeshes to the library NavMesh format, which enables me to use the library path-finding on NavMeshes from my real levels.<\/p>\n
But there is already a problem: the path-finding behaves weirdly and sometimes IA makes huge detours to get to some point. It seems to be a known issue… This is because of the NavMesh topology: a “good” NavMesh for the A* library is supposed to have some kind of grid pattern on it to avoid big triangles next to small triangles. Unluckily, NavMesh generation in Unity doesn’t expose some “grid size” or “max edge length” parameters, which means I can’t test that the path-finding behaves correctly with a “good” NavMesh.<\/p>\n
IV – Another new lib : RAIN<\/h3>\n
I heard about another path-finding library: RAIN. Totally Free, but sparse documentation. I tested it mainly to assess its NavMesh generation algorithm and hurrah! It can generated “grid”-NavMeshes. So I write another script to convert RAIN NavMeshes to A* NavMeshes, with very few documentation… Tough time! And… I get a few errors during the convertion but the NavMesh seems to be generated anyway. I test it with the A* path-finding, and it seems OK! The IA behaves well.<\/p>\n
Now, by combining 2 external libs, I have some basic IA behavior. I am at the same point that with Unity path-finding before.
\nI must now tackle the REAL problem: dynamic NavMesh\/IA loading.<\/p>\nV – NavMesh dynamic loading<\/h3>\n
It seems the A* library provides a way to export a NavMesh in a text file to load it dynamically at run time. Exactly what I need (theorically \ud83d\ude09 ). After a few tests, it seems to work at least for “little” files. But of course loading a new NavMesh gets rid of the previous one. I have to be cautious while activating\/deactivating IA agents. But this means I need to write another script to convert the A* NavMesh in a text file during level generation.<\/p>\n
- Use a 3rd-party library<\/b>. I must find one that does NavMesh generation and path-finding, is real-time, and dynamically loads levels.<\/li>\n
- Wait for a bug fix<\/b> from Unity about the NavMesh+LoadLevelAdditiveAsync problem. I don’t think it will come before I release my game, the Unity guys have loads to do and this is not a priority.<\/li>\n
- LoadLevelAdditiveAsync<\/b>: Same thing, but adds the content of the new level to the current one. This is obviously what I’m going for here.<\/li>\n<\/ul>\n
![\"\"](\"http:\/\/3.bp.blogspot.com\/-w9pdyuPfX-E\/UwZuoqHTWII\/AAAAAAAAHpU\/9sBsfWyxJlA\/s1600\/20140220_220709.png\")
<\/a><\/div>\n![\"\"](\"http:\/\/1.bp.blogspot.com\/-fco-vNu-xVo\/UwZ4p0N7Y2I\/AAAAAAAAHp4\/dYYW6JPEs_8\/s1600\/20140220_worldMesh.jpg\")
<\/a><\/div>\n