From fd9d6dafd12348e7ecd0aab216dfeda1fe13a088 Mon Sep 17 00:00:00 2001
From: "Danilo M." <danix@danix.xyz>
Date: Mon, 9 Nov 2026 19:43:48 +0100
Subject: feat: paint the virtual monitor with the first monitor's swaybg
 wallpaper

---
 deck-it               |  1 +
 deckit/display.py     | 55 ++++++++++++++++++++++++++++++++++++++++++++-------
 tests/test_display.py | 11 +++++++++++
 3 files changed, 60 insertions(+), 7 deletions(-)

diff --git a/deck-it b/deck-it
index 1463b5e..56927e5 100755
--- a/deck-it
+++ b/deck-it
@@ -25,6 +25,7 @@ teardown() {
     pkill -f "^bash $SELF watch" 2>/dev/null
     pkill -x wayvnc
     pkill -f '^python3 -m deckit' 2>/dev/null
+    pkill -f "^[^ ]*swaybg -o $MON( |$)" 2>/dev/null
     hyprctl output remove "$MON" >/dev/null 2>&1
     local s
     for s in $(adb devices | awk 'NR > 1 && $2 == "device" {print $1}'); do
diff --git a/deckit/display.py b/deckit/display.py
index f4d85f4..50fa3f6 100644
--- a/deckit/display.py
+++ b/deckit/display.py
@@ -1,8 +1,10 @@
 """The virtual monitor half: a headless Hyprland output sized to the tablet."""
 
 import json
+import os
 import re
 import shutil
+import signal
 import subprocess
 import sys
 import time
@@ -35,8 +37,35 @@ def hypr_lua(cfg: dict) -> bool:
     return mode == "lua"
 
 
-def setup_display(cfg: dict, run_cmd=None) -> None:
+def _swaybg_for(output: str, proc: Path = Path("/proc")):
+    """(pid, image, mode) of the swaybg process painting `output`, from /proc."""
+    for cmdline in proc.glob("[0-9]*/cmdline"):
+        try:
+            argv = cmdline.read_bytes().decode(errors="replace").split("\0")
+        except OSError:
+            continue
+        if not argv or not argv[0].endswith("swaybg"):
+            continue
+        out = image = None
+        mode = "fill"
+        for i, arg in enumerate(argv):
+            if i + 1 >= len(argv):
+                break
+            if arg == "-o":
+                out = argv[i + 1]
+            elif arg == "-i":
+                image = argv[i + 1]
+            elif arg == "-m":
+                mode = argv[i + 1]
+        if out == output and image:
+            return int(cmdline.parent.name), image, mode
+    return None
+
+
+def setup_display(cfg: dict, run_cmd=None, popen=None) -> None:
     run_cmd = run_cmd or run
+    popen = popen or (lambda cmd: subprocess.Popen(
+        cmd, start_new_session=True, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL))
     d = cfg.get("display", {})
     mon = d.get("name", "TAB")
     monitors = json.loads(run_cmd(["hyprctl", "monitors", "-j"]) or "[]")
@@ -51,11 +80,23 @@ def setup_display(cfg: dict, run_cmd=None) -> None:
                  f'hl.monitor({{output="{mon}", mode="{mode}", position="{pos}", scale={scale}}})'])
     else:
         run_cmd(["hyprctl", "keyword", "monitor", f"{mon},{mode},{pos},{scale}"])
-    tool = shutil.which("awww") or shutil.which("swww")
-    if d.get("wallpaper", True) and tool:
+    if d.get("wallpaper", True):
         others = [m["name"] for m in monitors if m["name"] != mon]
-        for line in run_cmd([tool, "query"]).splitlines():
-            if others and others[0] in line and "image: " in line:
-                run_cmd([tool, "img", "-o", mon, line.split("image: ", 1)[1]], timeout=10)
-                break
+        tool = shutil.which("awww") or shutil.which("swww")
+        if tool:
+            for line in run_cmd([tool, "query"]).splitlines():
+                if others and others[0] in line and "image: " in line:
+                    run_cmd([tool, "img", "-o", mon, line.split("image: ", 1)[1]], timeout=10)
+                    break
+        elif shutil.which("swaybg"):
+            # swaybg runs one process per output; copy the first monitor's image.
+            source = next((found for name in others if (found := _swaybg_for(name))), None)
+            if source:
+                existing = _swaybg_for(mon)
+                if existing:
+                    try:
+                        os.kill(existing[0], signal.SIGTERM)
+                    except OSError:
+                        pass
+                popen(["swaybg", "-o", mon, "-i", source[1], "-m", source[2]])
     print(f"{mon}: {mode} at {pos}")
diff --git a/tests/test_display.py b/tests/test_display.py
index b5d5b11..b69759a 100644
--- a/tests/test_display.py
+++ b/tests/test_display.py
@@ -1,4 +1,5 @@
 import sys
+import tempfile
 from pathlib import Path
 
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
@@ -21,5 +22,15 @@ class Resolution(unittest.TestCase):
             "2560x1600")
 
 
+class Swaybg(unittest.TestCase):
+    def test_finds_the_image_for_an_output(self):
+        root = Path(tempfile.mkdtemp())
+        d = root / "123"
+        d.mkdir()
+        (d / "cmdline").write_bytes(b"/usr/bin/swaybg\0-o\0DP-1\0-i\0/a.png\0-m\0fill\0")
+        self.assertEqual(display._swaybg_for("DP-1", root), (123, "/a.png", "fill"))
+        self.assertIsNone(display._swaybg_for("TAB", root))
+
+
 if __name__ == "__main__":
     unittest.main()
-- 
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