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Intersecting and De-intersecting in UT Maps
by "Hook" - 7/3/02

Building maps is not restricted to just using cubes and cylinders, and intersecting brushes is not only useful to create movers.
First of all, I will describe the basic functions of the Intersect and De-Intersect buttons.
Intersect: Intersecting always leaves the part of the red builder brush that is into a solid object, whereas De-Intersecting always leaves the part of the red builder brush that is into a subtracted open area. I will give you an example for you to try so you will be able to understand this and see for yourself how these work.
Make a room subtracted out of the world such as a good-sized cube. Now resize the builder brush to about one third the size of the room cube. Move the red builder brush so that about one half of it is in one of the walls. Now hit the intersect button. The half of the red brush that was inside the solid wall is all that remains and is perfectly butting the wall edge. Now hit the subtract button. There will be a cube subtracted out of the wall and ONLY the wall. Now hit the build button on the cube dialog box again. The red brush is back to its original size again. Move the red brush so that it is half way into the wall in a different place in the room. Hit the De-Intersect button this time. The half of the red brush that was outside the solid wall is all that remains this time and is perfectly butting the wall edge. Now hit the add button. There will be a cube added outside of the wall and ONLY outside of the wall. Remember! You must NEVER add into any part of a solid area and you must NEVER subtract into any part of a subtracted open area! Never!

Intersect and De-Intersect can also be a very useful way of forcing complex brushes to conform to other awkward shapes in your maps and can be used to create shapes that aren't so easy to make using the 2D editor. To give you an example, I'm going to demonstrate making a staircase like the one in the picture below. Ordinarily it's not a brush you can create in the usual ways. (Picture not included, yet)

1) Create an ordinary room and place a large cylinder, upright in the center as in the screenshot. Rebuild the map.
2) Then create a staircase brush and position it so that the bottom half of the staircase overlaps the cylinder (as below)
3) Now, here's where the de-intersect or intersect icon comes in to play. Whether you click on intersect or de-intersect is dependent on where the pivot point (the vertex shaped like a small red star) is positioned. If it's positioned outside the solid cylinder, you need to click "de-intersect". If it's positioned inside the cylinder, you need to click on "intersect". You should see your brush look like the one in the picture below. If you made a mistake simply build the original staircase brush and choose the other icon instead. (Still not sure about this part. I included this part just to let you try it out. Hook)
4) Now add this brush to your world (obviously you need to select a texture first)
5) Next delete the large cylinder that was there in the first place and rebuild. You should now have your special staircase.

Intersecting is a useful tool to take a complex set of brushes and change them into just one brush. This will often improve performance, as fewer polygons will have to be drawn (even though the same amount of nodes will actually be visible).
See the Custom Objects tutorial for more information on using Intersecting to consolidate multi-brush objects into one custom object!

That is it! Any questions let me know!