The Brush Order is very important. Because brushes in the Unreal Engine are ordered, the BSP cuts are made following the brush order. Most commonly, there are two brushes that combine to create a final shape. Firstly the subtractive brush, then the additive brush. This seems simple, as the order is as follows:
The Subtractive Brush is first, creating the basic shape of the room to be created, then the Additive brush follows, creating the additional features for the room.
However, there is often the need for more than two brushes to make up a particular shape. Another example would be the following:
We want a simple room, with a pillar in the middle of it, with a hole in the pillar that a player can see through.
While the order of brushes is not often an issue, complex maps and possible display problems can sometimes warrant the need to change the order of brushes. The Unreal Editor will automatically set the order of brushes based on the order that they are created in making editing much easier, but the concept of brush order is an important one, so lets explain it in more detail.
Click here for a detailed explanation of a simple room
This example shows the room described above, and shows the potential pitfalls if the order of the brushes is not correct. Reading through this example will explain just how the brush order will affect the environment and what is created.
[ Click here for printable version ]