I would like to use ikiwiki to build a static site which needs some transformations to be made on binary assets. A simple example is to translate a .odp presentation to .pdf using (e.g.) unoconv. If I add a new .odp attachment, or push one into the repo, I want the corresponding .pdf to appear in the generated site. What's the right place to hook in to do this?

I've made an experimental prototype which hooks into needsbuild, builds the pages then and there, and at the same time removes them from the list of pages to be built.

sub needsbuild {
    my $files=shift;
    my $nfiles=[];
    foreach my $f (@$files) {
        if ($f =~ /\.odp$/) {
            my $g = $f;
            $g =~ s/\.odp$/\.pdf/;
            debug("building $f to $g");
            will_render($f, $g);
            if (system("unoconv","-f","pdf","-o",IkiWiki::dirname("$config{destdir}/$g"),srcfile($f)) != 0) {
                error("unoconv: failed to translate $f to $g");
        else {
            push @$nfiles, $f;
    return $nfiles;

It appears to work, but is this the right way to do it, bearing in mind ikiwiki's dependency tracking and the like? And is the usage of will_render() correct?