backend/app/modules/masking.py

"""Inpaint mask construction from a floor footprint + item height (stage 5).

The mask is the silhouette of the item's 3D bounding box: the floor footprint
quad plus the same quad raised by the item's pixel height. The image-conditioned
inpaint then paints the reference furniture into exactly this region.
"""
from __future__ import annotations

from PIL import Image, ImageDraw, ImageFilter
from shapely.geometry import Polygon


def build_mask(
    image_size: tuple[int, int],
    footprint_quad: list[list[float]],
    height_px: float,
    feather: int = 6,
) -> tuple[Image.Image, tuple[int, int, int, int]]:
    """Return (mask, bbox). ``mask`` is an 'L' image, 255 = region to inpaint."""
    w, h = image_size
    pts = [(float(x), float(y)) for x, y in footprint_quad]
    raised = [(x, y - height_px) for x, y in pts]
    hull = Polygon(pts + raised).convex_hull
    coords = [(float(x), float(y)) for x, y in hull.exterior.coords]

    mask = Image.new("L", (w, h), 0)
    ImageDraw.Draw(mask).polygon(coords, fill=255)
    if feather > 0:
        mask = mask.filter(ImageFilter.GaussianBlur(feather))

    xs = [c[0] for c in coords]
    ys = [c[1] for c in coords]
    bbox = (
        max(0, int(min(xs))),
        max(0, int(min(ys))),
        min(w, int(max(xs))),
        min(h, int(max(ys))),
    )
    return mask, bbox