common: flesh out enum lab_edge and prefer over wlr_edges/wlr_direction

I like the new common/edge.h. I don't like how inconsistently we use it.

Current situation:

 - enum wlr_edges and wlr_direction are designed to be used as bitset,
   and are defined compatibly

 - enum lab_edge is *also* designed to be used as bitset, but
   incompatible with the others (LEFT/RIGHT come before UP/DOWN)

 - we use an inconsistent mix of all three *AND* uint32_t (usually with
   the WLR_EDGE constants rather than the LAB_EDGE constants), and
   convert between them on an ad-hoc basis, sometimes implicitly

Let's clean this up:

 - reorder enum lab_edge to be compatible with the two wlr enums
   (check this by static_assert)

 - use TOP/BOTTOM naming rather than UP/DOWN (matches wlr_edges)

 - add constants for the remaining possible combinations of the 4 edges

 - use lab_edge for all internal edge/direction fields, consistently

 - add lab_edge_is_cardinal() as a sanity check before casting to
   enum wlr_direction, and then eliminate all of direction.c/h

Instead of "enum wlr_edges direction", we now have
"enum lab_edge direction" which is not that much better. At least we
are now clear that we're overloading one enum with two meanings.

include/common/direction.h

@@ -1,11 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-#ifndef LABWC_DIRECTION_H
-#define LABWC_DIRECTION_H
-
-#include <wlr/types/wlr_output_layout.h>
-#include "common/edge.h"
-
-bool direction_from_edge(enum lab_edge edge, enum wlr_direction *direction);
-enum wlr_direction direction_get_opposite(enum wlr_direction direction);
-
-#endif /* LABWC_DIRECTION_H */

include/common/edge.h

@@ -2,34 +2,77 @@
 #ifndef LABWC_EDGE_H
 #define LABWC_EDGE_H
 
-#include <wayland-server-core.h>
+#include <stdbool.h>
 
 /**
- * Represents an edge or direction (e.g. window tiling, window motion)
+ * Unified/overloaded enum representing edges, corners, and directions.
+ * Used in many different contexts (moving, resizing, tiling) and with
+ * somewhat different semantics depending on context.
+ *
+ * Examples:
+ *   - LAB_EDGE_TOP can also mean "up" or "north".
+ *   - LAB_EDGES_TOP_LEFT can mean "top left corner" or "northwest".
+ *
+ * The enum is designed to be used as a bitset, and combinations of
+ * edges typically mean what you'd expect from the context. For example,
+ * LAB_EDGES_TOP_LEFT is used when resizing a view from its top-left
+ * corner, or when tiling a view in the top-left corner of an output.
+ *
+ * All 16 possible combinations of TOP/BOTTOM/LEFT/RIGHT are listed for
+ * completeness. Not all combinations make sense in all contexts.
+ *
+ * LAB_EDGE_NONE is sometimes used to mean "invalid".
+ *
+ * LAB_EDGE_ANY means "any edge or combination of edges (except NONE)"
+ * and is distinct from LAB_EDGE_ALL (which means all 4 edges).
+ *
+ * LAB_EDGE_TOP/BOTTOM/LEFT/RIGHT match the corresponding values of
+ * enum wlr_edges and enum wlr_direction, so that conversion between
+ * enums can be done with a simple cast.
  */
 enum lab_edge {
-	LAB_EDGE_INVALID = 0,
+	LAB_EDGE_NONE = 0,
 
-	LAB_EDGE_LEFT = (1 << 0),
-	LAB_EDGE_RIGHT = (1 << 1),
-	LAB_EDGE_UP = (1 << 2),
-	LAB_EDGE_DOWN = (1 << 3),
+	LAB_EDGE_TOP = (1 << 0),    /* or UP */
+	LAB_EDGE_BOTTOM = (1 << 1), /* or DOWN */
+	LAB_EDGE_LEFT = (1 << 2),
+	LAB_EDGE_RIGHT = (1 << 3),
 	LAB_EDGE_CENTER = (1 << 4), /* for window tiling */
 	LAB_EDGE_ANY = (1 << 5), /* for window rules */
 
-	/* for window tiling */
-	LAB_EDGE_UPLEFT = (LAB_EDGE_UP | LAB_EDGE_LEFT),
-	LAB_EDGE_UPRIGHT = (LAB_EDGE_UP | LAB_EDGE_RIGHT),
-	LAB_EDGE_DOWNLEFT = (LAB_EDGE_DOWN | LAB_EDGE_LEFT),
-	LAB_EDGE_DOWNRIGHT = (LAB_EDGE_DOWN | LAB_EDGE_RIGHT),
+	/* corners or ordinal directions (NW/NE/SW/SE) */
+	LAB_EDGES_TOP_LEFT = (LAB_EDGE_TOP | LAB_EDGE_LEFT),
+	LAB_EDGES_TOP_RIGHT = (LAB_EDGE_TOP | LAB_EDGE_RIGHT),
+	LAB_EDGES_BOTTOM_LEFT = (LAB_EDGE_BOTTOM | LAB_EDGE_LEFT),
+	LAB_EDGES_BOTTOM_RIGHT = (LAB_EDGE_BOTTOM | LAB_EDGE_RIGHT),
+
+	/* opposite edges */
+	LAB_EDGES_TOP_BOTTOM = (LAB_EDGE_TOP | LAB_EDGE_BOTTOM),
+	LAB_EDGES_LEFT_RIGHT = (LAB_EDGE_LEFT | LAB_EDGE_RIGHT),
+
+	/* all 4 edges */
+	LAB_EDGES_ALL = (LAB_EDGE_TOP | LAB_EDGE_BOTTOM |
+			LAB_EDGE_LEFT | LAB_EDGE_RIGHT),
+
+	/* 3-edge combinations (for completeness) */
+	LAB_EDGES_EXCEPT_TOP = (LAB_EDGES_ALL ^ LAB_EDGE_TOP),
+	LAB_EDGES_EXCEPT_BOTTOM = (LAB_EDGES_ALL ^ LAB_EDGE_BOTTOM),
+	LAB_EDGES_EXCEPT_LEFT = (LAB_EDGES_ALL ^ LAB_EDGE_LEFT),
+	LAB_EDGES_EXCEPT_RIGHT = (LAB_EDGES_ALL ^ LAB_EDGE_RIGHT),
 };
 
 enum lab_edge lab_edge_parse(const char *direction, bool tiled, bool any);
 
+/**
+ * Returns true if edge is TOP, BOTTOM, LEFT, or RIGHT
+ * (i.e. one of the four cardinal directions N/S/W/E)
+ */
+bool lab_edge_is_cardinal(enum lab_edge edge);
+
 /**
  * lab_edge_invert() - select the opposite of a provided edge
  *
- * Returns LAB_EDGE_INVALID for edges other than UP/DOWN/LEFT/RIGHT.
+ * Returns LAB_EDGE_NONE for edges other than TOP/BOTTOM/LEFT/RIGHT.
  *
  * @edge: edge to be inverted
  */