+#no warnings qw(recursion);
+
+sub subdivide_triangle ($$) {
+ my ($t, $fn) = @_;
+
+ #print STDERR 'SUBDIV', Dumper($t, $fn);
+
+ my @mids;
+ foreach my $ix (0..2) {
+ my $jx = ($ix+1) % 3;
+ my @midp;
+ foreach my $ci (0..2) {
+ push @midp, 0.5 * ($t->[$ix][$ci] + $t->[$jx][$ci]);
+ }
+ push @mids, \@midp;
+ }
+ foreach my $ix (0..2) {
+ #print STDERR 'SUBDIV IX ', $ix, "\n";
+ my $kx = ($ix+2) % 3;
+ $fn->([ $t->[$ix], $mids[$ix], $mids[$kx] ]);
+ }
+ #print STDERR 'SUBDIV MID\n';
+ $fn->(\@mids);
+}
+
+sub append_triangle ($) {
+ my ($t) = @_;
+ push @$output, $t;
+}
+
+#---------- project-cylinder ----------
+
+our $project_cylinder_radius;
+our $project_cylinder_max_d_theta;
+
+sub project_cylinder_triangle_need_subdivide ($) {
+ my ($t) = @_;
+ my @thetas = map { $_->[0] / $project_cylinder_radius } @$t;
+
+ foreach my $ix (0..2) {
+ if (abs($thetas[$ix] - $thetas[($ix+1)%3])
+ > $project_cylinder_max_d_theta) {
+ return 1;
+ }
+ }
+ return 0;
+}
+
+sub project_cylinder_need_subdivide () {
+ foreach my $t (@$triangles) {
+ next unless project_cylinder_triangle_need_subdivide $t;
+ return 1;
+ }
+ return 0;
+}
+
+sub project_cylinder_tri {
+ my ($t) = @_;
+
+ #print STDERR 'PROJECT', Dumper($t);
+
+ my $radius = $project_cylinder_radius;
+
+ my @ot;
+ foreach my $p (@$t) {
+ my ($x,$y,$z) = @$p;
+ my $r = $radius - $y;
+ my $theta = $x / $radius;
+ push @ot, [ $r * sin($theta),
+ -$r * cos($theta),
+ $z ];
+ }
+ append_triangle \@ot;