Make Ikiwiki resize images deterministically

As seen in #12566 (closed), if we do something like:

[[!img introduction_to_gnome_and_the_tails_desktop/keyboard.png size="267x" link="no" alt="Menu in the top-right corner of the desktop to switch between different keyboard layouts"]]

the resulting resized image contains a timestamp => breaks reproducibility.

Ikiwiki does the resizing in IkiWiki/Plugin/img.pm, using an interface to ImageMagick. I think Ikiwiki just have to tell PerlMagick to do the equivalent of convert +set date:create +set date:modify -define png:exclude-chunk=time to fix this.

The two +set ... things can be accomplished with:

--- a/IkiWiki/Plugin/img.pm
+++ b/IkiWiki/Plugin/img.pm
@@ -174,6 +174,9 @@ sub preprocess (@) {
                my $r = $im->Read("$format:$srcfile\[$pagenumber]");
                error sprintf(gettext("failed to read %s: %s"), $file, $r) if $r;

+                $im->Set('date:create' => NULL);
+                $im->Set('date:modify' => NULL);
+
                if (! defined $im->Get("width") || ! defined $im->Get("height")) {
                        error sprintf(gettext("failed to get dimensions of %s"), $file);
                }

but perhaps we only want to do this if SOURCE_DATE_EPOCH is set, and then set it to that value instead of NULL?

Note that we still may need to find how to tell PerlMagick to do -define png:exclude-chunk=time.

Parent Task: #5630 (closed)

Related issues

• Related to #12566 (closed)

Original created by @anonym on 12625 (Redmine)