vincentbernat.i3wm-configuration/bin/wallpaper

#!/usr/bin/env python3

# Build a multi screen wallpaper

# First argument is the directory where the wallpapers can be
# found. We use xinerama to know the dimension of each screen.

import os
import random
import argparse
import tempfile
import collections
import itertools

from Xlib import display
from Xlib.ext import randr

from PIL import Image

parser = argparse.ArgumentParser()
parser.add_argument(
    "-d",
    "--directory",
    default=".",
    help="search for images in DIRECTORY",
)
parser.add_argument(
    "-t",
    "--target",
    default="background.png",
    help="write background to FILE",
)
parser.add_argument(
    "--extra-images",
    default=3,
    metavar="N",
    help="consider N additional images to choose the best combination",
)
parser.add_argument(
    "--compression", default=0, type=int, help="compression level when saving"
)
options = parser.parse_args()
background = None

# Get display size
d = display.Display()
screen = d.screen()
window = screen.root.create_window(0, 0, 1, 1, 1, screen.root_depth)
background = Image.new("RGB", (screen.width_in_pixels, screen.height_in_pixels))

# Query randr extension
Output = collections.namedtuple("Output", ["x", "y", "width", "height"])
outputs = []
screen_resources = randr.get_screen_resources_current(window)
for output in screen_resources.outputs:
    output_info = randr.get_output_info(window, output, screen_resources.timestamp)
    if output_info.crtc == 0:
        continue
    crtc_info = randr.get_crtc_info(window, output_info.crtc, output_info.timestamp)
    outputs.append(Output(crtc_info.x, crtc_info.y, crtc_info.width, crtc_info.height))
if not outputs:
    outputs.append(Output(0, 0, (background.width, background.height)))

# Get all possible rectangles from outputs
candidates = []
for output in outputs:
    candidates.append(output)
    for ooutput in outputs:
        if ooutput == output:
            continue
        if output.x > ooutput.x or output.y > ooutput.y:
            continue
        candidates.append(
            Output(
                output.x,
                output.y,
                ooutput.x - output.x + ooutput.width,
                ooutput.y - output.y + ooutput.height,
            )
        )

# Get all rectangle combinations to cover outputs without overlapping
groups = []
for r in range(len(candidates)):
    for candidate in itertools.combinations(candidates, r + 1):
        for output in outputs:
            nb = 0
            for c in candidate:
                if c.x <= output.x < c.x + c.width and c.y <= output.y < c.y + c.height:
                    nb += 1
            if nb != 1:  # output not contained in a single rectangle
                break
        else:
            groups.append(candidate)

# Get random images
images = []
for base, _, files in os.walk(os.path.join(options.directory)):
    for i in files:
        if os.path.splitext(i)[1].lower() in (".jpg", ".jpeg", ".png", ".webp"):
            images.append(os.path.join(base, i))
images = random.sample(images, len(outputs) * options.extra_images)
images = [Image.open(image) for image in images]

# Find optimal combination for images
best_association = None
best_score = 0
for group in groups:
    for association in (zip(group, p) for p in itertools.permutations(images)):
        score = 0
        association = list(association)
        for output, image in association:
            # Similar ratio
            oratio = output.width * 100 // output.height
            iratio = image.width * 100 // image.height
            r = iratio / oratio
            if r > 1:
                r = 1 / r
            score += r * 100
            # Similar scale (when cropped)
            opixels = output.width * output.height
            ipixels = image.width * image.height * r
            r = ipixels / opixels
            if r >= 1:
                r = 1
            score += r * 50
        score /= len(group)
        if score > best_score or best_association is None:
            best_association = association
            best_score = score

print(
    "wallpaper: {}".format(
        " + ".join(
            "`{}` ({}×{})".format(
                image.filename[(len(options.directory) + 1) :], *image.size
            )
            for image in [couple[1] for couple in best_association]
        )
    )
)

for couple in best_association:
    output = couple[0]
    image = couple[1]

    # Find the right size for the screen
    imx, imy = output.width, image.height * output.width // image.width
    if imy < output.height:
        imx, imy = image.width * output.height // image.height, output.height
    if image.size != (imx, imy):
        image = image.resize((imx, imy), Image.LANCZOS)
    image = image.crop(
        (
            (imx - output.width) / 2,
            (imy - output.height) / 2,
            imx - (imx - output.width) / 2,
            imy - (imy - output.height) / 2,
        )
    )
    background.paste(image, (output.x, output.y))

# Save
assert background, "Don't know the size of the display area"
with tempfile.NamedTemporaryFile(
    delete=False, dir=os.path.dirname(os.path.realpath(options.target))
) as tmp:
    background.save(tmp, "png", compress_level=options.compression)
    os.rename(tmp.name, options.target)