Linedef type 503
Linedef type 503, Scroll Tagged Wall (Accelerative), is a type of linedef special which scrolls the front side textures of every tagged linedef along a given direction and at a specified speed. Unlike linedef type 502, the speed can be changed in an accelerative/decelerative fashion. Note that it will also scroll any player climbing on the front side of any affected linedef.
The length of the linedef indicates the base scrolling speed (32 fracunits of length equal one fracunit per tic), however the actual visible scrolling speed is set differently as explained ahead. The direction of the linedef indicates the direction of the scrolling.
On its own, this linedef will not scroll the wall texture. Rather, the texture will move whenever either the floor or ceiling of the control sector moves, which can done by using linedef executors. The actual scrolling speed, in any given instant, is equal to the base speed × the distance the control sector has moved + the speed in the previous instant. In other words, every time the control sector's floor or ceiling rises, the scroller accelerates, and every time the floor or ceiling lowers, the scroller decelerates. If the floor and ceiling are returned to their original heights, the scroller will stop, and if they are lowered past this point, the scroller will accelerate in the reverse direction.
To keep things simple and easier to control, the best thing to do is just use a base speed of 1 fracunit per tic (by giving the control linedef a length of 32 fracunits), and control the scrolling speed by moving the floor or ceiling of the control sector.
- Example file: ex_ld503_scrollwall_accelerative.wad (MAP01)
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