Displacement Y
displace-y
The displace-y parameter sets how far a displace map may move pixels vertically. Without it — and without displace-x — the map is read but nothing moves.
The value is in output pixels, multiplied by dpr, and is clamped to ±999. Vertical movement is driven by the map’s green channel, where 127 is neutral.
Setting only one axis is common: a map of horizontal folds needs displace-y alone, and leaving displace-x unset keeps the design from smearing sideways.
The layer forms are mark-displace-y and blend-displace-y.