feat(launcher): restore custom SD background experience

Buildscripts/generate-launcher-background.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+
+"""Convert an image to an uncompressed LVGL RGB565 launcher background."""
+
+import argparse
+import shutil
+import struct
+import subprocess
+from pathlib import Path
+
+
+LV_IMAGE_HEADER_MAGIC = 0x19
+LV_COLOR_FORMAT_RGB565 = 0x12
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(
+        description=(
+            "Create an uncompressed LVGL .bin image for "
+            "/sdcard/tactility/launcher/background.bin. Use a square image sized "
+            "to the display's longest edge to support both orientations without scaling "
+            "(for example, 320x320 for a 320x240 display)."
+        )
+    )
+    parser.add_argument("input", type=Path, help="Source image")
+    parser.add_argument("output", type=Path, help="Destination .bin file")
+    parser.add_argument("--width", type=int, required=True, help="Output width")
+    parser.add_argument("--height", type=int, required=True, help="Output height")
+    return parser.parse_args()
+
+
+def main() -> None:
+    args = parse_args()
+    if args.width <= 0 or args.width > 65535 or args.height <= 0 or args.height > 65535:
+        raise SystemExit("width and height must be between 1 and 65535")
+
+    magick = shutil.which("magick")
+    if magick is None:
+        raise SystemExit("ImageMagick is required (the 'magick' command was not found)")
+
+    command = [
+        magick,
+        str(args.input),
+        "-resize",
+        f"{args.width}x{args.height}^",
+        "-gravity",
+        "center",
+        "-extent",
+        f"{args.width}x{args.height}",
+        "-depth",
+        "8",
+        "rgb:-",
+    ]
+    rgb888 = subprocess.run(command, check=True, stdout=subprocess.PIPE).stdout
+    expected_size = args.width * args.height * 3
+    if len(rgb888) != expected_size:
+        raise SystemExit(f"unexpected ImageMagick output: {len(rgb888)} bytes, expected {expected_size}")
+
+    rgb565 = bytearray(args.width * args.height * 2)
+    for source_offset in range(0, len(rgb888), 3):
+        r, g, b = rgb888[source_offset : source_offset + 3]
+        pixel = ((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3)
+        destination_offset = (source_offset // 3) * 2
+        struct.pack_into("<H", rgb565, destination_offset, pixel)
+
+    stride = args.width * 2
+    header = struct.pack(
+        "<BBHHHHH",
+        LV_IMAGE_HEADER_MAGIC,
+        LV_COLOR_FORMAT_RGB565,
+        0,
+        args.width,
+        args.height,
+        stride,
+        0,
+    )
+
+    args.output.parent.mkdir(parents=True, exist_ok=True)
+    args.output.write_bytes(header + rgb565)
+    print(
+        f"Wrote {args.output} ({args.width}x{args.height}, "
+        f"{len(header) + len(rgb565)} bytes, uncompressed RGB565)"
+    )
+
+
+if __name__ == "__main__":
+    main()