Linedef type 515
Linedef type 515, Scroll Ceiling Texture (Displacement), is a type of linedef special which scrolls every tagged sector's ceiling flat without carrying Objects touching the ceiling. Unlike linedef type 513, it can be specifically set to start and stop at defined intervals.
The direction of the control linedef determines the direction the ceiling flat will scroll. 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.
On its own, this linedef will not scroll the ceiling. Rather, the flat will move whenever either the floor or ceiling of the control sector moves, which can done by using linedef executors. The actual scrolling speed is equal to the base speed × the control sector's movement speed. The direction of the scroll will be reversed if the floor or ceiling height of the control sector is lowered instead of raised.
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.
If this linedef is used in conjunction with linedef type 401, the scroller will immediately jump to the specified distance. If this linedef is used in conjunction with linedef type 404, the scroller will move continuously until the control sector reaches the given ceiling height. If this linedef is used in conjunction with linedef type 407, the scroller will only work as long as the linedef executor is being continuously triggered.
- Example file: ex_ld515_scrollceilingtexture_displacement.wad (MAP01)
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