Originally posted by Mind Maze
No, the question wasn´t what is BSP was:
What are BSP holes many people talk around?
What to do with rebuild BSP (Optimal, lame, good and minimize cuts or optimal)
I made a room with slime and a bridge there but there´s a "crack" which I don´t know what is it. In some angles viewing the slime at one side I see the HOM effect in a small part there.
Hi Mind Maze,
BSP stands for Binary Space Partitioning. When you compile your map, the computer takes the geometry you've supplied (Add and Subtract brushes) and creates a 'BSP Map.'
During compilation, the valid player space is recursively subdivided and the results are stored in a binary tree which tells the Unreal Engine where the player can and can't go (collision map) and what he can or can't see depending on his location in the map. Because of the need to keep map file sizes managable, you can only recursively subdivide the player space a certain number of times, since the BSP map grows exponentially with each iteration. So sometimes it's possible to make NO mistakes while building a map and to still get BSP holes. Like Zodiak mentioned, this often happens in the vicinity of very complex brushes. The brushes complexity exceeds the number of BSP iterations, and so the engine can't tell if the area is actually inside or outside the map. Because of the way decorative brushes interact, sometimes moving the brush slightly can help.
Try moving the detail brush slightly and rebuilding. This can change the way the engine partitions up the space around the brush and get rid of those BSP holes. The BSP view in the 3D window can help find these holes for you. (You'll need to re-build to update the BSP.)
You can also position the brush so it doesn't actually come into contact with the wall or floor (make it "float" 1 or 2 units above the floor or away from the wall). If the Add brush doesn't actually touch the floor/wall then it won't cut up the floor/walls BSP. This is a good trick to use with decorations like boxes, light fixtures, etc)
You can make the brush a semi-solid. Only Add brushes can be made semi-solid. Switch to the wire-frame view and left click on your brush to highlight it. Then right click on it and select "Make semi-solid" from the Solidity sub-menu. The brush will turn pink if you did it correctly. Now switch to the BSP view. Remember that this BSP view was generated the last time you re-built the map so, it won't show the changes you just made(this is why it's so important to re-build after changing your map geometry). Re-Build. You should see a BIG reduction in the number of BSP cuts. Fewer cuts means the map will run faster, so this is a great way to optimize your map for speed.
The only downside to semi-solid brushes is that they don't have proper collision maps, so it's possible under certain circumstances to fall through or walk through a semi-solid brush (usually if you're touching different parts of the same brush at once, like a single brush that serves as a ledge AND a wall). You can always change a semi-solid brush back to solid if any weirdness happens.
Last of all, you can always cover up a BSP hole by covering it up with an Add brush (add a thin rectangular Add brush over the hole). It's not an elegant solution, but it works.
--Nut
When life gives you a lemon, say 'Lemons? I like lemons. What else have you got?'