* ssa-retime : implement 'drift' mode

bin/ssa-retime

@@ -8,6 +8,7 @@ use utf8;
 use Getopt::Long;
 use Subtitle::Format::SSA;
 use Subtitle::TimePoint;
+use Subtitle::Utils ':timing';
 
 my @points;
 
@@ -141,12 +142,45 @@ if ($mode eq 'framerate') {
 } elsif ($mode eq 'drift') {
   if ($points[0]->time >= 0.2) {
     # add starting point
-    my $p = Subtitle::TimePoint->new;
+    my $p = Subtitle::TimePoint->new(time => 0.0, shift => 0.0);
-    $p->parse('0/0');
     unshift @points, $p;
   }
-  # add endpoint
+  # add endpoint, if needed
-  ...;
+  my $maxtime = 0.0;
+  foreach my $e (@{ $ssa->events }) {
+    next unless $e->t_end > $maxtime;
+    $maxtime = $e->t_end;
+  }
+  if ($maxtime > $points[-1]->time) {
+    my $p = Subtitle::TimePoint->new(time => $maxtime, shift => 0.0);
+    push @points, $p;
+  }
+  # dump points list
+  print "Final points list:\n";
+  foreach my $p (@points) {
+    printf "- %d:%02d:%02d.%03d ~ %.3f\n", make_timing($p->time), $p->shift;
+  }
+  print "-" x 30, "\n";
+  # real retime
+  $ssa->sort_events;
+  foreach my $e (@{ $ssa->events }) {
+    while ($points[1]->time <= $e->t_start) {
+      printf "move timepoints: %d:%02d:%02d.%03d (endpoint) <= %d:%02d:%02d.%03d (event)\n",
+        make_timing($points[1]->time), make_timing($e->t_start);
+      shift @points;
+    }
+    my ($a, $b) = @points;
+    my $pct = ($e->t_start - $a->time) / ($b->time - $a->time);
+    my $abs = ($a->shift > $b->shift)
+            ? ($a->shift - $b->shift)
+            : ($b->shift - $a->shift);
+    my $mod = ($a->shift > $b->shift)
+            ? ($a->shift - $abs * $pct)
+            : ($a->shift + $abs * $pct);
+    $e->t_start($e->t_start + $mod);
+    $e->t_end  ($e->t_end   + $mod);
+    printf "- %d:%02d:%02d.%03d ~ %.3f\n", make_timing($e->t_start), $mod;
+  }
 }
 
 if ($opts{outfile}) {