Add Visualiser widget

Adds a new `Visualiser` widget to provide an audio visualiser in the
bar. The widget relies on `cava` for the audio analysis and offloads
then generation of the image data to a separate script which is not
constrained by qtile's event loop.

It's probably got lots of bugs in but is good enough to merge now!

CHANGELOG

@@ -1,3 +1,4 @@
+2022-09-19: [FEATURE] Add `Visualizer` widget
 2022-09-16: [BUGFIX] Fix transparency issue in `PowerLineDecoration`
 2022-09-13: [FEATURE] Add clipping to `RectDecoration`
 2022-09-11: [FEATURE] Add grouping to `RectDecoration`

qtile_extras/resources/visualiser/cava_draw.py

@@ -0,0 +1,137 @@
+#!/usr/bin/env python
+
+# Copyright (c) 2022, elParaguayo. All rights reserved.
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+import argparse
+import signal
+from contextlib import contextmanager
+from multiprocessing import shared_memory
+from pathlib import Path
+from time import sleep
+
+import cairocffi
+from libqtile.utils import rgb
+
+
+def draw_cava(width, height, num_bars, pad, bar_width, spacing, pipe, background):
+    mem_size = width * height * 4
+    shm = shared_memory.SharedMemory(name="qte_cava_visualiser", create=True, size=mem_size)
+    lock = shared_memory.SharedMemory(name="qte_cava_lock", create=True, size=1)
+
+    # Create a context manager to lock access to shared memory to prevent race conditions
+    @contextmanager
+    def lock_memory(buf):
+        while buf[0]:
+            sleep(0.001)
+        buf[0] = 1
+        yield
+        buf[0] = 0
+
+    # Handler to tidy up shared memory objects if script is terminated
+    def kill_shm():
+        try:
+            shm.close()
+            shm.unlink()
+        except FileNotFoundError:
+            pass
+
+        try:
+            lock.close()
+            lock.unlink()
+        except FileNotFoundError:
+            pass
+
+    signal.signal(signal.SIGTERM, kill_shm)
+
+    surface = cairocffi.ImageSurface(cairocffi.FORMAT_ARGB32, width, height)
+    ctx = cairocffi.Context(surface)
+    buffer = shm.buf
+    lock_buffer = lock.buf
+    lock_buffer[0] = 0
+
+    with open(pipe, "rb") as reader:
+
+        while True:
+            out = reader.read(num_bars)
+
+            while out:
+                ctx.set_operator(cairocffi.OPERATOR_CLEAR)
+                ctx.rectangle(0, 0, width, height)
+                # ctx.set_source_rgb(0, 0, 0)
+                ctx.fill()
+                ctx.set_operator(cairocffi.OPERATOR_SOURCE)
+                x = pad
+                for bar in out:
+                    ctx.move_to(x, height)
+                    h = int(bar * height / 255)
+                    ctx.line_to(x, height - h)
+                    x += bar_width
+                    ctx.line_to(x, height - h)
+                    ctx.line_to(x, height)
+                    x += spacing
+
+                ctx.close_path()
+
+                ctx.set_source_rgba(*background)
+                ctx.fill()
+
+                with lock_memory(lock_buffer):
+                    buffer[:] = bytearray(surface.get_data())
+
+                out = reader.read(num_bars)
+
+            break
+
+
+if __name__ == "__main__":
+    # Tidy up left over shared memory files
+    for shm in ["qte_cava_lock", "qte_cava_visualiser"]:
+        p = Path("/dev/shm") / shm
+        if p.is_file():
+            p.unlink()
+
+    parser = argparse.ArgumentParser(description="Script to offload visualiser image generation.")
+    parser.add_argument("--width", dest="width", type=int, help="Image width", required=True)
+    parser.add_argument("--height", dest="height", type=int, help="Image height", required=True)
+    parser.add_argument("--bars", dest="num_bars", type=int, help="Number of bars", required=True)
+    parser.add_argument(
+        "--spacing", dest="spacing", type=int, help="Spacing between bars", required=True
+    )
+    parser.add_argument("--background", dest="background", type=rgb, help="Background colour")
+    parser.add_argument(
+        "--pipe", dest="pipe", type=str, help="Pipe for cava output", required=True
+    )
+
+    args = parser.parse_args()
+
+    bar_width = args.width // args.num_bars
+    pad = (args.width - (bar_width * args.num_bars)) // 2
+    bar_width -= args.spacing
+
+    draw_cava(
+        args.width,
+        args.height,
+        args.num_bars,
+        pad,
+        bar_width,
+        args.spacing,
+        args.pipe,
+        args.background,
+    )

qtile_extras/widget/__init__.py

@@ -42,6 +42,8 @@
     "TVHWidget": "tvheadend",
     "UnitStatus": "unitstatus",
     "UPowerWidget": "upower",
+    "Visualiser": "visualiser",
+    "Visualizer": "visualiser",
     "WordClock": "wordclock",
 }