PlacementMount2D

Typed value object for how a placed 2D object is mounted. The 2D sibling of PlacementMount. That class carries a 3D column plus an EDGE/FACE/CORNER/TOP socket key because in 3D "on top of" is a half-space derived from the host's bounding box. In 2D the placement grid is a TileMapLayer in the X/Y plane and there is no third axis to hang a socket off, so this contract uses a second, explicit occupancy axis instead of reusing one: key = (host_cell, host_slot, slot_index) Why not z_index: z_index is a render property in 2D. It is already spent on indicator layering (IndicatorFactory2D.DEFAULT_Z_INDEX = 150, preview at 200), so a stacking feature built on it would be a drawing trick with no occupancy meaning. The slot key below is a real placement fact. Admitted by PlacementWorldRegistry: the shared registry gates every record on a mount validator chosen by PlacementWorldRecord.dimension. PlacementWorldRecord.Dimension.TWO_D routes to is_valid_dict() here, and THREE_D keeps the 3D PlacementMount.is_valid_dict() unchanged — the two contracts are never widened into each other, and an unknown dimension keeps the 3D behaviour. A mount from to_dict() is therefore accepted by PlacementWorldRegistry.register() and survives the save boundary (validate_saved_states(), PlacementWorldRecord.to_save_data()) like any other mount. Slot geometry is grid-local: surface_size_cells is measured in CELLS, not pixels, so the same catalog works at any tile size. seat_offset_pixels() converts with the live tile size at the moment of placement. Deliberately additive: Type.CELL is 0 and every existing 2D save record still reads as a CELL mount, so a world written by a build without this file restores unchanged.

Source: addons/grid_placement/systems/building/2d/placement_mount_2d.gd

Syntax

class PlacementMount2D extends RefCounted

Members

Name	Kind	Summary
KEY_TYPE	Field	How a 2D object attaches to its world. CELL is the default and the only member before surface stacking existed. String keys used by to_dict() / from_dict(). Centralized so the service, persistence layer, and demo never spell them inline.
KEY_HOST_CELL	Field
KEY_HOST_SLOT	Field
KEY_SLOT_INDEX	Field
MIN_SURFACE_SIZE_CELLS	Field	A host declares its top surface in whole cells (or a fraction of one) on each axis. The surface is the rectangle [0, size) measured from the host's own grid seat, so slot (0,0) always exists for any host of at least 1x1.
MAX_SURFACE_SIZE_CELLS	Field	A host may not declare a surface larger than this on either axis. Bounds the slot count a single host can create so a typo in a catalog resource cannot make the slot space explode.
MAX_SLOT_INDEX	Field	Largest slot_index a surface mount may claim. Bounds hostile save data: a record claiming slot 2^30 would otherwise allocate a validation loop that long. Real hosts stay far below this.
type	Property
host_cell	Property	The grid cell the HOST occupies (its minimum corner for a multi-cell host).
host_slot	Property	The host's stacked height in cells, counting from its own seat upward. 0 = a ground-level object that offers no surface.
slot_index	Property	Which slot of that height band the stacked object claims.
entry	Property	In-memory only. Not serialized: a Resource does not survive a JSON round-trip, so the restore side supplies it explicitly.
for_cell	Method
for_surface	Method
m	Property
is_surface	Method
slot_key	Method
band_key	Method
slot_count_for	Method
surface_extent_cells	Method
slot_cell_offset	Method
BAND_CLEARANCE_CELLS	Field	Cells of clear space one stacked band leaves above the surface it stacks on, on top of the surface's own depth. Exposed as a constant because it is the one number that makes the two occupancy axes resolve in the same unit: p_slot_index walks the surface in cells, and the band must do the same or the identity has no position at all.
band_lift_cells	Method
seat_offset_pixels	Method
extent	Property
col_row	Property
from_min_corner	Property
from_center	Property
to_dict	Method
from_dict	Method
is_valid_dict	Method
apply_to	Method