fix focus <direction> with negative gaps (#5333)

fixes #5293

src/tree.c

@@ -470,7 +470,11 @@ static Con *get_tree_next_workspace(Con *con, direction_t direction) {
         return NULL;
     }
 
-    Output *current_output = get_output_containing(con->rect.x, con->rect.y);
+    // Use the center of the container instead of the left/top edges, to make
+    // this work with negative gaps. See https://github.com/i3/i3/issues/5293
+    const uint32_t x = con->rect.x + (con->rect.width / 2);
+    const uint32_t y = con->rect.y + (con->rect.height / 2);
+    Output *current_output = get_output_containing(x, y);
     if (!current_output) {
         return NULL;
     }

testcases/t/549-focus-wrapping-gaps.t

@@ -0,0 +1,48 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • https://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • https://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • https://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Ensure focus wrapping works with negative gaps
+# Ticket: #5293
+# Bug still in: 4.21-130-ged690c7b
+use i3test i3_autostart => 0;
+
+my $config = <<EOT;
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+gaps inner 10
+gaps outer -2
+
+fake-outputs 1024x768+0+0,1024x768+1024+0
+EOT
+
+my $pid = launch_with_config($config);
+
+cmd 'focus output fake-0, workspace left';
+my $left = open_window;
+
+cmd 'focus output fake-1, workspace right';
+my $right = open_window;
+
+is($x->input_focus, $right->id, 'right window focused');
+
+cmd 'focus left';
+
+is($x->input_focus, $left->id, 'left window focused');
+
+exit_gracefully($pid);
+
+done_testing;