3 files changed, 70 insertions, 0 deletions

diff --git a/include/wlr/types/wlr_output_layout.h b/include/wlr/types/wlr_output_layout.h
index 7dd2b16a..ea96c6b8 100644
--- a/include/wlr/types/wlr_output_layout.h
+++ b/include/wlr/types/wlr_output_layout.h
@@ -5,6 +5,7 @@
 #include <wayland-util.h>
 #include <wlr/types/wlr_box.h>
 #include <wlr/types/wlr_output.h>
+#include <wlr/util/direction.h>
 
 struct wlr_output_layout_state;
 
@@ -96,4 +97,12 @@ void wlr_output_layout_add_auto(struct wlr_output_layout *layout,
 struct wlr_output *wlr_output_layout_get_center_output(
 		struct wlr_output_layout *layout);
 
+/**
+ * Get the closest adjacent output to the reference output from the reference
+ * point in the given direction.
+ */
+struct wlr_output *wlr_output_layout_adjacent_output(
+		struct wlr_output_layout *layout, enum wlr_direction direction,
+		struct wlr_output *reference, double ref_x, double ref_y);
+
 #endif
diff --git a/include/wlr/util/direction.h b/include/wlr/util/direction.h
new file mode 100644
index 00000000..b5f3a589
--- /dev/null
+++ b/include/wlr/util/direction.h
@@ -0,0 +1,11 @@
+#ifndef WLR_UTIL_DIRECTION_H
+#define WLR_UTIL_DIRECTION_H
+
+enum wlr_direction {
+	WLR_DIRECTION_UP = 0,
+	WLR_DIRECTION_DOWN = 1,
+	WLR_DIRECTION_LEFT = 2,
+	WLR_DIRECTION_RIGHT = 4,
+};
+
+#endif
diff --git a/types/wlr_output_layout.c b/types/wlr_output_layout.c
index db0389bd..24982e98 100644
--- a/types/wlr_output_layout.c
+++ b/types/wlr_output_layout.c
@@ -421,3 +421,53 @@ struct wlr_output *wlr_output_layout_get_center_output(
 
 	return wlr_output_layout_output_at(layout, dest_x, dest_y);
 }
+
+
+struct wlr_output *wlr_output_layout_adjacent_output(
+		struct wlr_output_layout *layout, enum wlr_direction direction,
+		struct wlr_output *reference, double ref_x, double ref_y) {
+	// XXX should we allow reference to be NULL?
+	assert(reference);
+
+	struct wlr_box *ref_box = wlr_output_layout_get_box(layout, reference);
+
+	double min_distance = DBL_MAX;
+	struct wlr_output *closest_output = NULL;
+	struct wlr_output_layout_output *l_output;
+	wl_list_for_each(l_output, &layout->outputs, link) {
+		if (reference != NULL && reference == l_output->output) {
+			continue;
+		}
+		struct wlr_box *box = wlr_output_layout_output_get_box(l_output);
+
+		bool match = false;
+		// test to make sure this output is in the given direction
+		if (direction | WLR_DIRECTION_LEFT) {
+			match = box->x + box->width <= ref_box->x || match;
+		}
+		if (direction | WLR_DIRECTION_RIGHT) {
+			match = box->x >= ref_box->x + ref_box->width || match;
+		}
+		if (direction | WLR_DIRECTION_UP) {
+			match = box->y + box->height <= ref_box->y;
+		}
+		if (direction | WLR_DIRECTION_DOWN) {
+			match = box->y >= ref_box->y + ref_box->height;
+		}
+		if (!match) {
+			continue;
+		}
+
+		// calculate distance from the given reference point
+		double x, y;
+		wlr_output_layout_closest_point(layout, l_output->output,
+			ref_x, ref_y, &x, &y);
+		double distance =
+			(x - ref_x) * (x - ref_x) + (y - ref_y) * (y - ref_y);
+		if (distance < min_distance) {
+			min_distance = distance;
+			closest_output = l_output->output;
+		}
+	}
+	return closest_output;
+}