Concave Brushes

A concave object is something that has an inward angle. Such as the keys on a keyboard, they all have inward faces curved to your finger.

Here’s a concave object:

Concave objects are not allowed in maps. When compiling a map Hammer must be able to enter the brush face at one angle and exit it at the same angle. And if the brush is Concave it would collide with itself. This creates Invalid Objects. Here is an example of some Illegal Objects and there legal alternatives:

As you can see, all I did was split the brush into more brushes. To view a list of the Objects and other errors in the map press Alt + P  This brings up the Map Problems window.

As you can see from the three invalid brushes i made, they are illegal and have shown up as “Invalid Solid Structure”. You can just click Fix one them, but it would turn them all Convex; and this may ruin your brush, depending on how concave it is. You should try to make it convex yourself by clipping it into separate brushes.

As you can see in the pentagon, the light (blue lines) can pass over the face without hitting any other part of the brush. However, on the other object on the right, only three of the faces the light can pass over. On the other two faces the light hits itself.

When you are finishing mapping and about to close hammer, check your map for invalid solid structures. If you close a map with illegal objects in it Hammer will try and fix them the same way clicking ‘Fix’ on the Map Problems window does. Otherwise it will delete them and you will get a message when you re-open the file saying “for your information X objects were now loaded due to errors”.