makeicns.sh: produce Big Sur+ style macOS app icon

The previous script generated a 1024x1024 icon from the SVG with no
squircle background and no transparent padding, which caused macOS
to render the Dock/Finder icon noticeably larger than first-party
apps and without the rounded-square shape users expect.

Rewrite the script to follow Apple's Big Sur+ icon template:

  - 1024x1024 canvas
  - 824x824 white squircle, centered (100px transparent padding outside)
  - Artwork rendered at 560x560, centered inside the squircle
  - Squircle corner radius ~22.5% of the squircle size

Use rsvg-convert to rasterize the SVG (ImageMagick crops this
particular SVG when rendering directly), then composite onto the
squircle background in two steps for reliability.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/makeicns.sh

@@ -3,8 +3,15 @@ set -e
 
 usage() {
     cat <<EOF
-$0: Make a macOS icns file from an SVG with ImageMagick and iconutil.
+$0: Make a macOS icns file from an SVG with rsvg-convert, ImageMagick and iconutil.
-usage: $0 [SVG [ICNS [ICONSET]]
+
+Follows the Big Sur+ icon template:
+  - 1024x1024 canvas with a rounded-square (squircle) background
+  - Icon artwork scaled to fit inside an 824x824 content area, centered
+  - Transparent padding outside the squircle so the Dock/Finder render it
+    like other first-party macOS apps.
+
+usage: $0 [SVG [ICNS [ICONSET]]]
 
 ARGUMENTS
     SVG     The SVG file to convert
@@ -28,15 +35,55 @@ iconset="${3:-./target/icon.iconset}"
 
 set -u
 
-mkdir -p "$iconset"
+workdir="$(dirname "$iconset")/icon-work"
-magick "$svg" -background none -resize 1024x1024 "$iconset"/icon_512x512@2x.png
+rm -rf "$iconset" "$workdir"
-magick "$svg" -background none -resize 512x512 "$iconset"/icon_512x512.png
+mkdir -p "$iconset" "$workdir"
-magick "$svg" -background none -resize 256x256 "$iconset"/icon_256x256.png
+
-magick "$svg" -background none -resize 128x128 "$iconset"/icon_128x128.png
+# Big Sur+ macOS icon template proportions (in a 1024 canvas):
-magick "$svg" -background none -resize 64x64 "$iconset"/icon_32x32@2x.png
+#   canvas  = 1024
-magick "$svg" -background none -resize 32x32 "$iconset"/icon_32x32.png
+#   squircle = 824  (the white rounded-square background, inset 100px)
-magick "$svg" -background none -resize 16x16 "$iconset"/icon_16x16.png
+#   content  = 560  (artwork inside the squircle, with generous margin)
-cp "$iconset"/icon_512x512.png "$iconset"/icon_256x256@2x.png
+#   radius   = 185  (~22.5% of the squircle, the characteristic curvature)
-cp "$iconset"/icon_256x256.png "$iconset"/icon_128x128@2x.png
+CANVAS=1024
-cp "$iconset"/icon_32x32.png "$iconset"/icon_16x16@2x.png
+SQUIRCLE=824
+CONTENT=560
+RADIUS=185
+BG_COLOR="#FFFFFF"
+SQUIRCLE_OFFSET=$(( (CANVAS - SQUIRCLE) / 2 ))
+CONTENT_OFFSET=$(( (CANVAS - CONTENT) / 2 ))
+
+# 1) Render the SVG to the content size at full fidelity.
+#    rsvg-convert handles our SVG correctly; ImageMagick sometimes crops it.
+rsvg-convert -w "$CONTENT" -h "$CONTENT" "$svg" -o "$workdir/content.png"
+
+# 2) Draw the rounded-square (squircle) background on a transparent canvas.
+#    The squircle is inset from the canvas edges (transparent padding), so the
+#    Dock/Finder render it at the same visual size as other first-party apps.
+magick -size ${CANVAS}x${CANVAS} xc:none \
+    -fill "$BG_COLOR" \
+    -draw "roundrectangle ${SQUIRCLE_OFFSET},${SQUIRCLE_OFFSET} $((CANVAS-SQUIRCLE_OFFSET-1)),$((CANVAS-SQUIRCLE_OFFSET-1)) $RADIUS,$RADIUS" \
+    "$workdir/background.png"
+
+# 3) Composite the artwork onto the background, centered inside the content area.
+magick "$workdir/background.png" \
+    "$workdir/content.png" -geometry +${CONTENT_OFFSET}+${CONTENT_OFFSET} -composite \
+    "$workdir/icon-1024.png"
+
+# 4) Generate each iconset size from the master so all sizes share the same
+#    squircle proportions and look consistent at every resolution.
+for size in 1024 512 256 128 64 32 16; do
+    magick "$workdir/icon-1024.png" -resize ${size}x${size} "$workdir/${size}.png"
+done
+
+cp "$workdir/1024.png" "$iconset"/icon_512x512@2x.png
+cp "$workdir/512.png"  "$iconset"/icon_512x512.png
+cp "$workdir/512.png"  "$iconset"/icon_256x256@2x.png
+cp "$workdir/256.png"  "$iconset"/icon_256x256.png
+cp "$workdir/256.png"  "$iconset"/icon_128x128@2x.png
+cp "$workdir/128.png"  "$iconset"/icon_128x128.png
+cp "$workdir/64.png"   "$iconset"/icon_32x32@2x.png
+cp "$workdir/32.png"   "$iconset"/icon_32x32.png
+cp "$workdir/32.png"   "$iconset"/icon_16x16@2x.png
+cp "$workdir/16.png"   "$iconset"/icon_16x16.png
+
 iconutil -c icns "$iconset" -o "$icns"