Dithered sun

"""A sun and its halo in ordered Bayer dither."""

import numpy as np

from walldye import (
    ACCENT,
    ACCENT_3,
    ACCENT_4,
    ACCENT_7,
    BG,
    BG_ALT,
    Canvas,
    Rect,
    by_regime,
    design,
    mix,
)
from walldye.field import cells, falloff
from walldye.pixel import dither, grid_runs

CELL = 4  # a finer cell pushes the whole halo past the file-size limit
R_SUN, R_HALO = 170, 840  # the solid disc, and where the last dots give out
# The halo from the outside in. On paper BG_ALT would make the outermost step a veil darker
# than the one inside it, so there it is ACCENT_7 alone.
LAYERS = (
    by_regime(mix(BG_ALT, ACCENT_7, 0.47), ACCENT_7),
    mix(BG, ACCENT_4, 0.37),
    ACCENT_4,
    ACCENT_3,
    ACCENT,
)


@design(aspects="any")
def draw(s: Canvas) -> None:
    c = s.pick(landscape=(0.6875, 0.52), portrait=(0.56, 0.36), snap=CELL)
    # the grid is anchored on the sun, so the halo's dither stays put as the sun moves
    halo = Rect(-R_HALO, -R_HALO, 2 * R_HALO, 2 * R_HALO)
    xs, ys = cells(halo, CELL)
    r = np.hypot(xs, ys)
    # squared, so the rings crowd close to the sun and the last one spreads wide
    tone = falloff(r - R_SUN, R_HALO - R_SUN, power=2)
    level = dither(tone, len(LAYERS), method="bayer", matrix=8)
    level[r < R_SUN] = len(LAYERS)
    # Each layer is drawn whole over the one outside it, so its runs carry on under the next
    # and only its own ring breaks into cells: about half the runs of one flat index grid.
    with s.motif(c, R_HALO, handle=R_SUN, cell=CELL):
        for k, paint in enumerate(LAYERS, start=1):
            grid_runs(s, (level >= k).astype(np.int64), [None, paint], CELL, (-R_HALO, -R_HALO))