From Valve Developer Community
What is a leak?
Levels created with the Source Engine must be completely internally sealed. No part of the interior of the level, the "world", must connect with the outside, the "Void". Even the sky must be sealed off with a brush using the
tools/toolsskybox texture. When there is any kind of gap to the void, a leak is generated when the map is compiled by
vbsp. When a leak occurs, the tools cannot know which part of the level is inside, and what part is outside, and
vvis cannot be run. If vvis is not run several effects may not work or look right including water and some surface properties like dust puffs.
This example shows a map with an obvious gap in the geometry, leading to the void. This will generate a leak error message when it is compiled:
When a map like this is compiled, with a gap to the void, vbsp generates an error similar to this in the compile log:
ProcessBlock_Thread: 0...1...2...3...4...5...6...7...8...9...10 (0) **** leaked **** Entity light (-1607.69 -1094.12 -183.00) leaked!
With this error message, vbsp is telling you that there has been a leak in the level, and the first entity it found when attempting to get into the level from the void (in this case, a light entity). It also gives you the location of that entity, expressed in X, Y, and Z world unit coordinates.
Effects of leaks
A leak in a level has a number of bad effects. First, the
vbsp process will report the leak, and it will not produce a portal file (
mapname.prt). The portal file is used by the
vvis process to perform its visibility calculations. Since there is no portal file,
vvis will not run at all. When
vvis doesn't run, it doesn't produce the files necessary for the
vrad process to calculate its light bounces. Due to this, the
vrad process will only perform direct lighting - no light bounces.
The most serious effect by far is that the
vvis process will not run when a leak is present. When the level is run in the game, the rendering engine will not have any visibility info available with which to limit itself, so it will attempt to draw the entire level. This will most certainly lead to high polygon counts and may lead to sections of the map to render incorrectly or not at all.
Checking for leaks the fast way
The BSP part of your compile will always report any leaks it finds, but spending hours of full compile time and game execution just to find out that your map is broken after compilation, simply isn't efficient. If you have the slightest suspicion that your map might have a leak - normally when you've expanded the brushwork borders of the map - you can run a fast compile to check for BSP errors by opening the Run Map dialog, turning off VIS and RAD compile tools, and checking the Don't run game after compiling flag. The process of checking your entire map for leaks will only take about 8 seconds with this method.
Alternatively, you can use the advanced compilation mode and take advantage of the "check if file exists afterwards" feature. You can then simply check if the portal file was created or not. This will let you abort the compile, skipping vvis, vrad and launching the game, if there were any leaks. Note that this does not catch area portal leaks, but those are relatively rare.
Sometimes these gaps aren't quite as obvious as the above example. They can be as little as one unit wide and still cause a leak. The compile tools provide you with a pointfile to help you locate the leak. A pointfile is a file generated by
vbsp that draws a line between the void of the map to the entity it found during the leak check. After receiving a leak error in
mapname.lin file will be created in the same directory as your .vmf map file.
Loading a Pointfile
The pointfile can be loaded into the Hammer Editor to show you precisely where the leak is inside the level. To load a pointfile for the level, use the Load Pointfile command in the Map menu.
This image shows the pointfile loaded into the previous example. Notice that the red line appears in both the 3D and 2D views, and is traced back from the entity through the gap.Using this visual aid, you can find the source of the leak by following the red line to the outside of the level. It's best to start at the entity specified in the
vbsperror message, and then follow the line until you find the gap in the geometry. Close the gap and recompile the level to see if you have fixed the leak.
Finding the endpoint
If you're having trouble locating the start entity, you can use the Go to Coordinates command on the View menu to find the entity and the start of the pointfile line. Simply enter the coordinates given by
vbsp for the entity location, and the 2D and 3D views will be centered on that location. Follow the line to find your leak.
Another method to find the source of the leak is to zoom out in one or more of the 2D views. After loading the pointfile, zoom out until you see the red line. Follow the line until you reach the entity at the one of the endpoints. Then select the entity, and choose Center 3D Views on Selection from the View menu. Now you can follow the pointfile line to find the leak.
Other causes of leaks
Besides gaps in outside geometry, there are other map errors that can cause vbsp to generate a leak error.
Entities outside the level
func_door.Since brush entities do not block visibility, this will create the same condition as if there were a gap in their place. All entities must be inside valid level space, or the map will generate a leak. This is because vbsp determines the inside of the level depending on where it finds entities.
Improperly constructed areaportals
Leak error messages can also be generated when an areaportal does not properly seal the two areas it connects. Find leaks with areaportals using the same methods as geometry gap leaks.See areaportal for more information on the uses of areaportals.
Non-solid geometry does not seal the world
func_detailbrushes. None of these non-solid brush types will block visibility and seal the world. Attempting to use them in this way will generate a leak. You can fix this type of leak by adding a solid brush behind them to seal the map. Using a brush with the
tools/toolsnodrawmaterial will seal the map, but not add any additional rendering cost, so it's a great way to seal the map behind non-solid geometry.
Mismatched entity origins
A more subtle cause of leaks can be with any entities that have origin helpers, such as func_door_rotating or func_rot_button. While the entity itself may be inside the world, if the origin helper is outside the map, the entity will cause a leak. If you find a pointfile heading to a empty spot outside of the map, and there is no entity there, an origin helper is a good thing to look for.
One way to quickly tell if an entity origin is causing the leak is to:
- Load the pointfile.
- Find the endpoint(s) of the pointfile.
- Choose Select All from the Edit Menu.
- Make sure Show Helpers is checked on the View Menu.
- If you see an origin helper appear at the pointfile, you know that's the problem.
If you have an origin helper causing a leak, you can select the object and manually move the origin back into the world, use the Center Origins command from the Tools Menu, or simply right-click on the origin helper and select Center on entity.Mismatched entity origins usually occur when a brush entity with one of these helpers is moved while in Solids mode. Moving a brush entity in solids mode does not move the entity's origin helper.
There is a particular case where your geometry could be entirely sealed and yet a leak would constantly appear, even if you have absolutely no entity around the leak. If loading the pointfile doesn't help you at all, then you might be facing this particular situation. In this case, the red line would be passing through solid geometry. The cause is pretty simple - it is most likely that you have at least one of the brush sides textured with a translucent material. When this situation appears, the brush isn't able to seal anything anymore. In most cases, this will cause problems with areaportals that wouldn't be able to seal rooms. Remember that the sides in question could be located anywhere, even between other brushes.
Func_viscluster can also cause leaks, when they cross areaportal surfaces, or are too close to them. Disabling all func_visclusters and compiling to see if the leak is gone should be done, at least at last resort.
Conclusion: An ounce of prevention
Using the pointfile tools makes finding leaks relatively painless, but one of the most important ways to fix leaks is by preventing them in the first place. Taking your time when building, and making sure brushes are snapped properly to the grid can go a long way towards eliminating leaks before they occur. The cleaner and more organized your geometry, the more likely you are to be able to spot leaks when they occur, or even prevent them from happening in the first place. You can also help prevent lots of extra work by compiling your level as you go along, instead of building your whole level before trying to compile it. Finding one leak at a time while the map is only partially complete is a lot easier and faster than finding leaks in a complete map that is full of geometry.