logo: Switch from Inkscape to rsvg-convert / librsvg

This SVG implementation is more convenient than Inkscape's for
several reasons:

 * It's faster -- the runtime for the whole script goes from about
   5.5s down to 1.5s.

 * It doesn't include a redundant alpha layer (of a constant 0xff)
   in the output.  That makes all the PNG outputs smaller, and
   better yet lets us cut out the mess of ImageMagick `convert`
   we'd been using for stripping that layer in the one file where
   Apple forbids it.

 * Most concretely: it supports the `transform` CSS property.
   That will come in very handy in the next commit, to help us
   stitch together different pieces of the new icon design.

   For a useful table of which SVG implementations support which
   features, see this page from resvg:
     https://linebender.org/resvg-test-suite/svg-support-table.html
   (At the moment resvg isn't in Debian stable, though -- presumably
   because Rust packaging is somewhat hard -- so resvg itself was
   less convenient for me to use.)

Just like with the last couple of commits, this produces a visually
imperceptible change in the output files.  Examining with `sng`
shows some pixels did change slightly, and also that some metadata
got simpler.  Here's from [email protected]:

     IHDR {
         width: 40; height: 40; bitdepth: 8;
    -    using color alpha;
    -}
    -pHYs {xpixels: 6299; ypixels: 6299; per: meter;}  # (160 dpi)
    -tEXt {
    -    keyword: "Software";
    -    text: "www.inkscape.org";
    +    using color;
     }
    +bKGD {red: 255;  green: 255;  blue: 255;}

Others are similar but with width, height, xpixels, ypixels, and
the DPI figure all scaled up; and in [email protected] the old
version had no "alpha" but did have sections cHRM and gAMA.

Like with a couple of previous commits in this series, we leave
those changes out for now, in order to bundle them with
substantive changes coming next.

Author: gnprice

tools/generate-logos

@@ -35,17 +35,15 @@ die() {
     exit 1
 }
 
-inkscape --version >/dev/null 2>&1 \
-    || die "Need inkscape -- try 'apt install inkscape'."
+rsvg-convert --version >/dev/null 2>&1 \
+    || die "Need rsvg-convert -- try 'apt install librsvg2-bin'."
 
 cwebp -version >/dev/null 2>&1 \
     || die "Need cwebp -- try 'apt install webp'."
 
 jq --version >/dev/null 2>&1 \
     || die "Need jq -- try 'apt install jq'."
 
-strip-nondeterminism --version >/dev/null 2>&1 \
-    || die "Need strip-nondeterminism -- try 'apt install strip-nondeterminism'."
 
 
 # Suppose (for comments below) this points to a zulip.git worktree.
@@ -74,7 +72,7 @@ make_one_ios_app_icon() {
     local output_basename=Icon-"${size_pt}x${size_pt}@${scale}x".png
     local output="${iconset}"/"${output_basename}"
     if [ ! -f "${output}" ]; then
-        inkscape "${src_icon_square_beta}" -w "${size_px}" -o "${output}"
+        rsvg-convert "${src_icon_square_beta}" -w "${size_px}" -o "${output}"
     fi
 
     printf >>"${contents}" \
@@ -102,15 +100,6 @@ make_ios_app_icon() {
     make_one_ios_app_icon 76 2 ipad
     make_one_ios_app_icon 1024 1 ios-marketing
 
-    # For the App Store logo, it's required to not have transparency.
-    # We already don't have any intentional transparency, so just
-    # cut out the alpha channel.
-    mv "${iconset}"/Icon-1024x1024@1x{,.1}.png
-    convert "${iconset}"/[email protected] \
-      -alpha deactivate "${iconset}"/[email protected]
-    strip-nondeterminism "${iconset}"/[email protected]
-    rm -f "${iconset}"/[email protected]
-
     # From "Spotlight, Settings, and Notification Icons"
     # in the same iOS doc
     make_one_ios_app_icon 40 3 iphone
@@ -135,7 +124,7 @@ make_ios() {
 
 make_webp() {
     local input="$1" size="$2" output="$3"
-    inkscape "${input}" -w "${size}" -o "${tmpdir}"/tmp.png
+    rsvg-convert "${input}" -w "${size}" -o "${tmpdir}"/tmp.png
     # `cwebp -z 9` means lossless, and max/slowest compression
     cwebp -z 9 "${tmpdir}"/tmp.png -o "${output}"
 }