Default value
FLOAT_PLANE
Possible values
-10000 to 10000 (integers only),
FLOAT_PLANE+p
The value of plane overrides layer, and is mainly used for non-topdown map formats like isometric. Positive values are drawn on top, and negative values are drawn below. This mostly deprecates EFFECTS_LAYER and BACKGROUND_LAYER, but they can still be useful when using PLANE_MASTER for effects (see appearance_flags).
The special value FLOAT_PLANE can be used for images and overlays, to take on the plane of the parent atom. Whenever an icon or icon_state is used directly as an overlay, this is its plane. If there is no parent atom, the plane is 0.
You can also use FLOAT_PLANE as a relative value, so FLOAT_PLANE+1 adds 1 to the parent atom’s plane. This may be useful for some applications where an object is included in visual contents. The added value should still be kept in the range of -10000 to 10000, or preferably much smaller.