Common (Windows): optimises ico generation

src/common/windows/c-logo.sh

@@ -1,10 +1,34 @@
 #!/bin/sh
-# Convert logo.svg to logo.ico
-rsvg-convert -w 16 -h 16 logo.svg > logo16.png
-rsvg-convert -w 32 -h 32 logo.svg > logo32.png
-rsvg-convert -w 48 -h 48 logo.svg > logo48.png
-rsvg-convert -w 64 -h 64 logo.svg > logo64.png
-rsvg-convert -w 128 -h 128 logo.svg > logo128.png
-rsvg-convert -w 256 -h 256 logo.svg > logo256.png
-convert logo16.png logo32.png logo48.png logo64.png logo128.png logo256.png logo.ico
+# Convert logo.svg to logo.ico.
+#
+# Every frame is stored as PNG. ImageMagick's ICO writer only uses PNG for frames that are
+# 256x256 or larger and falls back to an uncompressed DIB for everything smaller, which
+# inflates the icon from ~19 KB to ~108 KB (and to ~370 KB on ImageMagick 7, which also
+# stores 256x256 as a DIB). Packing the frames here keeps the icon small and predictable.
+set -e
+
+cd "$(dirname "$0")"
+
+for size in 16 32 48 64 128 256; do
+    rsvg-convert -w "$size" -h "$size" ../../logo/logo.svg > "logo$size.png"
+done
+
+python3 - <<'PY'
+import struct
+
+sizes = [16, 32, 48, 64, 128, 256]
+frames = [open(f"logo{s}.png", "rb").read() for s in sizes]
+
+header = struct.pack("<HHH", 0, 1, len(sizes))
+offset = 6 + 16 * len(sizes)
+entries = b""
+for size, frame in zip(sizes, frames):
+    dim = 0 if size == 256 else size  # 0 means 256 in the ICO directory
+    entries += struct.pack("<BBBBHHII", dim, dim, 0, 0, 1, 32, len(frame), offset)
+    offset += len(frame)
+
+with open("logo.ico", "wb") as f:
+    f.write(header + entries + b"".join(frames))
+PY
+
 rm logo16.png logo32.png logo48.png logo64.png logo128.png logo256.png

src/common/windows/logo.svg

@@ -1 +0,0 @@
-../../logo/logo.svg