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#!/usr/bin/env python3
# udt-accent: pick a Catppuccin Macchiato accent matching a wallpaper.
# Copyright (C) 2026 Danilo M. <danix@danix.xyz>
# Licensed under the GNU General Public License v2 only.
"""Extract a wallpaper's signature color and snap it to a Macchiato accent.
Usage: udt-accent <wallpaper-path>
udt-accent --selftest
The extraction deliberately calls pywal's colorz backend directly rather than
running `wal -i`, because `wal -i` rewrites the whole ~/.cache/wal directory
including the terminal's ANSI colors. See the design spec for why that matters.
"""
import math
import os
import subprocess
import sys
import tempfile
from pathlib import Path
# The nine candidate accents. rosewater and flamingo are excluded as
# near-neutral tints that capture saturated inputs; maroon, sapphire and
# lavender are excluded as near-duplicate hues of red, sky and mauve.
ACCENTS = {
"pink": "#f5bde6",
"mauve": "#c6a0f6",
"red": "#ed8796",
"peach": "#f5a97f",
"yellow": "#eed49f",
"green": "#a6da95",
"teal": "#8bd5ca",
"sky": "#91d7e3",
"blue": "#8aadf4",
}
FALLBACK = "mauve"
MIN_CHROMA = 10.0
OUTPUT = Path.home() / ".cache" / "wal" / "udt-accent.rasi"
BORDER_OUTPUT = Path.home() / ".cache" / "wal" / "udt-border.lua"
def _to_lab(hexval):
"""Convert #rrggbb to CIELAB. sRGB D65, the standard conversion."""
r, g, b = (int(hexval[i:i + 2], 16) / 255 for i in (1, 3, 5))
def linear(c):
return c / 12.92 if c <= 0.04045 else ((c + 0.055) / 1.055) ** 2.4
r, g, b = linear(r), linear(g), linear(b)
x = (0.4124 * r + 0.3576 * g + 0.1805 * b) / 0.95047
y = (0.2126 * r + 0.7152 * g + 0.0722 * b)
z = (0.0193 * r + 0.1192 * g + 0.9505 * b) / 1.08883
def f(t):
return t ** (1 / 3) if t > 0.008856 else 7.787 * t + 16 / 116
fx, fy, fz = f(x), f(y), f(z)
return (116 * fy - 16, 500 * (fx - fy), 200 * (fy - fz))
def _hue(hexval):
"""Perceptual hue angle in radians."""
_, a, b = _to_lab(hexval)
return math.atan2(b, a)
def _chroma(hexval):
"""Distance from the neutral axis. Near-greys sit close to zero."""
_, a, b = _to_lab(hexval)
return math.hypot(a, b)
def snap(hexval):
"""Return the name of the nearest candidate accent by perceptual hue."""
if _chroma(hexval) < MIN_CHROMA:
return FALLBACK
target = _hue(hexval)
def distance(name):
delta = abs(_hue(ACCENTS[name]) - target)
return min(delta, 2 * math.pi - delta) # hue is circular
return min(ACCENTS, key=distance)
def signature_color(image):
"""Extract the image's most chromatic mid-tone color.
Calls the colorz backend directly. It returns a list and writes nothing,
which is what keeps the pywal cache (and so the terminal) untouched.
"""
from pywal.backends import colorz
colors = colorz.get(str(image), 16)
# Slot 0 trends near-black and the upper slots near-white; the signature
# color of an image lives in the middle.
return max(colors[1:7], key=_chroma)
def write_accent(name):
"""Write the accent rasi file atomically."""
hexval = ACCENTS[name]
content = (
"/* Generated by udt-accent. Do not edit. */\n"
f"* {{ accent: {hexval}ff; }}\n"
)
OUTPUT.parent.mkdir(parents=True, exist_ok=True)
# Write-then-rename: a rofi launch during a wallpaper change must never
# read a half-written file.
fd, tmp = tempfile.mkstemp(dir=str(OUTPUT.parent), suffix=".tmp")
try:
with os.fdopen(fd, "w") as handle:
handle.write(content)
os.replace(tmp, OUTPUT)
except BaseException:
if os.path.exists(tmp):
os.unlink(tmp)
raise
def hue_neighbours(name):
"""The accent either side of `name` on the perceptual hue wheel.
The animated border rotates a gradient, so it needs more than one colour to
show motion. Using the accent's own neighbours keeps the movement visible
while staying inside one region of the palette.
"""
order = sorted(ACCENTS, key=lambda n: _hue(ACCENTS[n]))
i = order.index(name)
return order[(i - 1) % len(order)], order[(i + 1) % len(order)]
def write_border(name):
"""Write the Hyprland border gradient, atomically.
Emitted as Lua rather than a .conf snippet: Hyprland's Lua parser refuses
`hyprctl keyword` ("keyword can't work with non-legacy parsers") and has no
source directive, so the config reads this file with dofile() instead.
"""
before, after = hue_neighbours(name)
stops = ", ".join(f'"rgb({ACCENTS[n].lstrip("#")})"' for n in (before, name, after))
content = (
"-- Generated by udt-accent. Do not edit.\n"
f"return {{ {stops} }}\n"
)
BORDER_OUTPUT.parent.mkdir(parents=True, exist_ok=True)
fd, tmp = tempfile.mkstemp(dir=str(BORDER_OUTPUT.parent), suffix=".tmp")
try:
with os.fdopen(fd, "w") as handle:
handle.write(content)
os.replace(tmp, BORDER_OUTPUT)
except BaseException:
if os.path.exists(tmp):
os.unlink(tmp)
raise
def main(image):
try:
name = snap(signature_color(image))
except Exception as exc:
# A broken image must still leave a working theme.
print(f"udt-accent: {exc}, falling back to {FALLBACK}", file=sys.stderr)
name = FALLBACK
write_accent(name)
write_border(name)
# Hyprland only rereads its config on request, and may not be running.
subprocess.run(["hyprctl", "reload"], capture_output=True, check=False)
before, after = hue_neighbours(name)
print(f"{name} {ACCENTS[name]} (border: {before} .. {name} .. {after})")
def selftest():
# Every accent must snap to itself, or the metric is not self-consistent.
for name, hexval in ACCENTS.items():
got = snap(hexval)
assert got == name, f"{name} ({hexval}) snapped to {got}"
# Representative real-world inputs.
assert snap("#ff8800") == "peach", snap("#ff8800")
assert snap("#00cc44") == "green", snap("#00cc44")
# A near-grey has an unstable hue angle and must take the fallback.
assert snap("#888888") == FALLBACK, snap("#888888")
# Border neighbours must be distinct from the accent and from each other,
# or the gradient has nothing to animate between.
for name in ACCENTS:
before, after = hue_neighbours(name)
assert len({before, name, after}) == 3, (name, before, after)
assert hue_neighbours("peach") == ("red", "yellow"), hue_neighbours("peach")
print("selftest OK")
if __name__ == "__main__":
if len(sys.argv) == 2 and sys.argv[1] == "--selftest":
selftest()
elif len(sys.argv) == 2:
main(sys.argv[1])
else:
print(__doc__, file=sys.stderr)
sys.exit(2)
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