Hint brush
Hint planes are used to split visleafs during compile time and, as such, are a way of optimising the results of the Vis map compile stage.
They are commonly referred to as hint "brushes" since they are placed in a map in the same way as a normal world brush. The hint plane is defined by the side of the brush that is covered with the tools/toolshint texture. Multiple hint planes can be defined by texturing multiple sides of the brush, or by using multiple brushes. The other sides of the brush that are not acting as hint planes must be covered with the tools/toolsskip texture; these faces will be ignored by the compiler.
Hints are automatically tied to their own visgroup, so you can easily hide them.
A number of example maps and a tutorial discussing their use can be found below.
Why and when to split visleafs
Note:Learning how visleafs work may aid the understanding of this article. (See that link.)Sometimes, certain leaf shapes are preferred over others simply because that shape makes those leafs see less other leafs. (which means less stuff to be rendered, thus a faster map).
The following illustrates the importance of visleaf cutting, and, at the same time, provides examples on where hints are useful.
The first example is almost the same as the SDK example map. This is a side view of a single room with players and pipes separated by a wall:
When a player is at either of the two player_starts, the Source engine, while rendering each frame, must consider whether the brushes (pipes) to the right of the wall should be drawn. That occurs because vbsp.exe did not do what would be the most efficient way of dividing our level into leafs:
From the leaf the players are in, the leaf the pipes are in can be seen and the pipes are drawn. Quite a shame, because those pipes cannot be seen from the players perspective (they are behind the wall in the center). We can use hints to steer the process of leaf-making, like so:
The white line is a side of a brush with the tools/toolshint texture. It forces vbsp.exe to divide our map into three leafs. In this case, there can be no straight line drawn from the leaf the players are in to the leaf the pipes are in. That is the essence of hinting.
Skyboxes are sometimes a bit high, causing a player to see a lot of stuff in the city because the leaf he is in can see over the houses. (like in the above example). That also is a good situation where one can use hints to stop the visibility.
Here are more examples:
Above is top view of a typical corner. There are two players (the green boxes) and the cylinders at each end represent a lot of stuff to be drawn for the engine. The goal with hinting in this case is avoid rendering objects when unnecessary, e.g. when a player is "around" the corner from the objects.
One may think vbsp.exe will make sure each player won't see the objects belonging to the other player. This is wrong. It will divide this "level" into two leaves, either cutting the leaves along the brown or pink line (vbsp.exe is not very predictable). Either way, one can see from one leaf to the other and the other player's stuff will be drawn. However, this situation can be greatly improved by simply by placing a hint at the corner, dividing our level into three leaves, (making a total of three instead of two) but making sure one player's stuff doesn't get rendered from the other player's point of view:
There is no direct line-of-sight between the red and brown leaves so unnecessary rendering is avoided. However, if one of the players moves into the green leaf, he will see both his and the other player's stuff rendered. You cannot stop that using hints. The only way to stop this would be by changing the level layout or by using other methods, like the ones described in Controlling Geometry Visibility and Compile Times
A last few examples:
Here a few examples of when and how to use Hints. In all cases the goal is to hide the green players from each other. The upper three work as they should. The left one illustrates that it doesn't even matter if its one hint-brush spanning the corner, as long as its angle is > 180 degrees the two players will not "see" each other's leaves because no straight line can be drawn between their leaves. The bottom-left example shows you that can happen when the angle is less than 180 degrees. One can easily draw a straight line from leaf to leaf, resulting in non-functional hints.
When the corner in the hallway is 180 degrees, as in the middle top picture, two hints will suffice. In fact, they can even be closer to the players, but that would increase their effectivity (more stuff will be drawn "around the corner". ) see the example below the middle. Because you lowered the hints, vbsp.exe is forces to cut up the top visleaf because visleafs can't be concave. No matter how vbsp.exe cuts up this corner, the hints will always work less effective AND create extra leafs (more work for vvis.exe). In our example, the left player can see leafs 1 and 2 (same surfaces as above), but the right player will see all three numbered leafs (which is more than the top example.).
The two right pictures show you you should keep things as simple as possible. If you can suffice using one hint, like in the top example, do so. And, don't use hints if you don't need to, like in the bottom picture. there is absolutely no way vbsp.exe can create leafs that enable both players to see each other, so there's no need to use hints here to hide the players from each other (you can offcourse use hints to hide parts of the hallways). In the same example you can also see a nice wall (the middle one) that should NEVER be a func_detail: because func_details don't exist according to vvis.exe, it will think both players will see each other and thats not what we want. vbsp.exe may even make it so both players here are in the same leaf.
A last example on when to use hints, is for simplifying your map. Sometimes, vbsp.exe cuts up your level into more leafs than neccesairy. This will only add to the compile time, so you don't want this. You can use hints to counteract this. For instance, place hints in doorways to stop the doorways to cut up the rooms they connect. Or, if you get an error that a certain visleaf is cornering too many other visleafs, you can use hints to cut that leaf into multiple leafs that corner a smaller amount of leafs.
In summary, since hints cost no extra power during the playing of your map, the are the primary way to speed up your map and controll your visibility.
See also
Examples
- sourcesdk_content\hl2\mapsrc\sdk_hints.vmf - The location of the SDK example map on how to make hint brushes, on your computer.
- http://www.akilling.org/akg/tutorials/wiseHINT.asp - Hint brush tutorial