Knowledge Base - Spiral Stair Using K²Bridge

Spiral Stair Using K²Bridge

Spiral Stairs
Figure 1: Spiral Stairs

Figure 1 shows a simple spiral staircase using the K²Bridge technique developed by Kurt Kesler. The example wad, sscase.wad illustrates the technique. (Looks like ROTT doesn't it? :) This is a true spiral staircase since the step-things overlap each other as shown on Figure 2.

Map Detail
Figure 2: Map Detail

Building the staircase was quite easy. I simply replaced the blocking sprite with a non-transparent image. I used the top of the green marble column to make the steps of the stairs as shown in Figure 3.

Sprite Replacement in Wintex
Figure 3: Sprite Replacement in Wintex

When you walk on the blocking sprite, you are walking on top of the sprite. Since the step was drawn at the bottom of the sprite, it looked like you were walking on air. I offset the sprite by 64 to make the step draw at the top, like a real step. Since I am using an existing sprite, I cannot set the offset greater than the height of the sprite which is approximately 64 units high (I'm not sure of the exact height), hence the lift to actually get on the stairs.

The tricky part is setting the offset. The first step has a Z setting of 328 as shown in Figure 4.

Offset of Sprite
Figure 4: Offset of Sprite

This may seem odd at first, but the offset is calculated from the ceiling not the floor. Remember this sprite hangs from the ceiling. The room has a ceiling of 384. 384 - 328 = 56 so the sprite is just below the lift height of 64. The next step has an offset of 304 or 24 units "higher". The staircase proceeds in this fashion in a square circle, the steps overlapping. The only problem with this setup is the fact that when you overlap the steps, they need to be separated by enough space so that the player can go under them.

The K²Bridge is a wonderful discovery and this is only one of a number of applications utilizing this new technique.


The K²Bridge was developed by Kurt Kesler.