# Knowledge Base - Using the Bridge Thing

## Using the Bridge Thing

Figure 1: A Working Bridge

Although ZDoom does not support true 3D sectors, the 3D effect can be achieved by using the new Bridge thing. The Bridge thing is an invisible, solid thing that the player can walk on and under to simulate a 3D environment.

The Bridge thing (9990) takes two parameters:

2. thickness: the thickness of the thing.

The radius will determine the width of your bridge. The thickness is how tall the bridge thing is and determines if the player can walk under the bridge.

Figure 2: Map Layout

To use a bridge thing simply place the thing on the map and set the radius and thickness. The Z height should be set so that the player can walk over the bridge. In Figure two the Z heights of the bridge things are 124. To calculate the proper Z height, subtract the thickness from the sector height.

In Figure 2, the thickness is set to 4 and they are placed over a sector that has a floor of -128. The bridge thing must have the same floor height as the right and left sectors to ensure a smooth transition across the bridge. Since the bridge sector is at -128, it is 128 below the 0 floors of the right and left sectors, so the Z height is 128 - 4 or 124. At this height, the bridge is at the same height as the left and right sectors. Since the bridge thing is invisible, textures were added to the bridge sectors to indicate the bridge direction.

The new bridge things are an easy way to add a 3D environment to any Doom map.

### Sources

ZDoom reference by Marisa Heit.

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