Switch from Imagemagick to Graphicsmagick.

Note that GM doesn't support gradient:angle so we
have to use a direction. It's radial, not linear,
but is completely acceptable.

Imagemagick silently introduces artifacts and fails
to composite images when the underlying gradient is
of the form { #AAAAAA --> #BBBBBB }, where R=G=B.

Note that { #AAAAAA --> #BBBBBC } works fine. This
is a real bug but isn't a wallpapers problem.

Add a 'prepare-docker' wrapper script, which simply
builds the tarball using a known Graphicsmagick and
not whichever happens to be on the generating system.

4 files changed, 24 insertions, 13 deletions

diff --git a/.gitignore b/.gitignore
index de54eb5..54885f2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 .DS_Store
 adelie-wallpapers-*.tar.xz
+adelie-wallpapers-*/
 build/
 output/
diff --git a/README b/README
index 669925c..d28d8bc 100644
--- a/README
+++ b/README
@@ -17,6 +17,7 @@ The only choices a contributor has are '<slug>' and
              /image.<ext>  <-- image    file
              /MANIFEST     <-- metadata file
         /prepare           <-- generator script
+        /prepare-docker    <-- for production only*
 
 
 building
@@ -27,7 +28,10 @@ building
 (2) ensure that you are checked out at a tag that has
     been pushed to origin
 
-(3) run the 'prepare' script with no arguments
+(3) run the 'prepare'* script with no arguments, or run
+    the 'prepare-docker' script to do this in a container
+    with a known version of imagemagick or graphicsmagick
+    if you are preparing for a release
 
 (4) upload the resulting tarball, in 'output/', to the
     distfiles mirror, directly under 'source/'
diff --git a/prepare b/prepare
index 16d000a..b1c3aa1 100755
--- a/prepare
+++ b/prepare
@@ -124,7 +124,7 @@ cd "${HERE}";
 ##
 # Check for required tools.
 #
-for k in curl composite convert; do
+for k in curl gm; do
     if ! command -v ${k} 2>&1 >/dev/null; then
         printf "E: required utility '%s' not found!\n" "${k}";
         exit 1;
@@ -239,12 +239,12 @@ size_only ()
 
 
             # resized
-            convert "${image}/${from_x}x${from_y}.png" -resize ${x}x${y}^ "${KEEP}"/${name}/${x}x${y}.${type};
+            gm convert "${image}/${from_x}x${from_y}.png" -resize ${x}x${y}^ "${KEEP}"/${name}/${x}x${y}.${type} 2>/dev/null;
         done
 
         # screenshot
         printf "      - Generating screenshot\n";
-        convert "${image}/${from_x}x${from_y}.png" -resize 400x250^ "${KEEP}"/${name}/screenshot.jpg;
+        gm convert "${image}/${from_x}x${from_y}.png" -resize 400x250^ "${KEEP}"/${name}/screenshot.jpg 2>/dev/null;
     done
 }
 
@@ -293,27 +293,25 @@ make_fake ()
     args="${@}";        # all remaining arguments
 
     printf "Generating %5s ('%s')...\n" "${size}" "${name}";
-    convert \
-        -define gradient:angle=65 \
+    gm convert \
+        -define gradient:direction=NorthEast \
         -size ${size} \
         gradient:"${hexa}"-"${hexb}" \
         "${name}" \
         ;
 
     # FIXME: this is literal magic?
-    composite \
-        \( \
+    gm composite \
         -compose atop \
         -gravity southwest \
         -background none \
         -resize ${size%x*}x$((${size#*x}*80/100)) \
         "${TEMP}"/polyguin.svg \
         -geometry +0+100 \
-        \) \
         "${name}" \
         "${name}" \
         ;
-    composite \
+    gm composite \
         -compose atop \
         -gravity southeast \
         -background none \
@@ -322,7 +320,7 @@ make_fake ()
         "${name}" \
         "${name}" \
         ;
-    convert \
+    gm convert \
         ${args} \
         "${name}" \
         "${name}" \
@@ -345,7 +343,7 @@ printf "%s\n" "${MAKE}" | while read ratio scale _; do
         "#bbbbbb" "#eeeeee" \
         black_x200 \
         "${TEMP}"/generated/background/${x}x${y}.png \
-        -colorspace Gray -separate -average \
+        -colorspace Gray \
         ;
 
     # lockscreen (full color)
@@ -375,7 +373,7 @@ make_real ()
     # TODO: add filename extension checker?
 
     printf "Generating %5s ('%s')...\n" "${size}" "${name}";
-    convert "${file}" -resize ${size}^ "${name}";
+    gm convert "${file}" -resize ${size}^ "${name}" 2>/dev/null;
 }
 
 
diff --git a/prepare-docker b/prepare-docker
new file mode 100755
index 0000000..4bf519f
--- /dev/null
+++ b/prepare-docker
@@ -0,0 +1,8 @@
+#!/bin/sh -e
+
+docker run -e UIDGID=$(id -u):$(id -g) -v"$(dirname $(readlink -f "${0}"))":/x -w/x --rm -i alpine:3.18 <<'EOF'
+apk add curl git graphicsmagick xz;
+git config --global --add safe.directory /x;
+/x/prepare;
+chown "${UIDGID}" $(find . -mindepth 1 -maxdepth 1 -type f -name 'adelie-wallpapers-*.tar.xz');
+EOF