edges, resistance, snap: unified resistance and snapping engine

include/edges.h

@@ -0,0 +1,110 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef LABWC_EDGES_H
+#define LABWC_EDGES_H
+
+#include <limits.h>
+#include "common/macros.h"
+
+struct border;
+struct output;
+struct view;
+
+static inline int
+clipped_add(int a, int b)
+{
+	if (b > 0) {
+		return a >= (INT_MAX - b) ? INT_MAX : (a + b);
+	} else if (b < 0) {
+		return a <= (INT_MIN - b) ? INT_MIN : (a + b);
+	}
+
+	return a;
+}
+
+static inline int
+clipped_sub(int a, int b)
+{
+	if (b > 0) {
+		return a <= (INT_MIN + b) ? INT_MIN : (a - b);
+	} else if (b < 0) {
+		return a >= (INT_MAX + b) ? INT_MAX : (a - b);
+	}
+
+	return a;
+}
+
+static inline int
+edge_get_best(int next, int edge, bool decreasing)
+{
+	if (!BOUNDED_INT(next)) {
+		/* Any bounded edge beats an unbounded next */
+		return BOUNDED_INT(edge) ? edge : next;
+	}
+
+	/* No unbounded edge ever beats next */
+	if (!BOUNDED_INT(edge)) {
+		return next;
+	}
+
+	/* Max edge wins for decreasing moves, min edge for increasing */
+	return decreasing ? MAX(next, edge) : MIN(next, edge);
+}
+
+/*
+ * edge_validator_t - edge validator signature
+ * @best: pointer to the current "best" edge
+ * @current: current position of a moving edge
+ * @target: position to which the moving edge will be moved
+ * @oppose: opposing edge of encountered region
+ * @align: aligned edge of encountered region
+ * @lesser: true if moving edge is top or left edge; false otherwise
+ *
+ * This function will be used by edge_find_neighbors and edge_find_outputs to
+ * validate and select the "best" output or neighbor edge against which a
+ * moving edge should be snapped. The moving edge has current position
+ * "current" and desired position "target". The validator should determine
+ * whether motion of the crosses the given opposed and aligned edges of a trial
+ * region and should be considered a snap point. An edge is "lesser" if it
+ * occupies a smaller coordinate than the opposite edge of the view region
+ * (i.e., it is a top or left edge).
+ *
+ * Opposing edges are on the opposite side of the target region from the moving
+ * edge (i.e., left <-> right, top <-> bottom). When the moving edge snaps to
+ * an opposing edge, the view should maintain the configured gap. Aligned edges
+ * are on the same side of the target region from the moving edge (i.e.,
+ * left <-> left, right <-> right, top <-> top, bottom <-> bottom). When the
+ * moving edge snaps to an aligned edge, the view should *not* include a gap.
+ *
+ * If window gaps are configured, all edges will be offset as appropriate to
+ * reflect the desired padding. Thus, the validator should generally compare
+ * the given current or target values directly to the opposing and aligned edge
+ * without regard for rc.gap.
+ *
+ * Any edge may take the values INT_MIN or INT_MAX to indicate that the edge
+ * should be effectively ignored. Should the validator decide that a given
+ * region edge (oppose or align) should be a preferred snap point, it should
+ * update the value of *best accordingly.
+ */
+typedef void (*edge_validator_t)(int *best,
+	int current, int target, int oppose, int align, bool lesser);
+
+void edges_initialize(struct border *edges);
+
+void edges_adjust_geom(struct view *view, struct border edges,
+	uint32_t resize_edges, struct wlr_box *geom);
+
+void edges_find_neighbors(struct border *nearest_edges, struct view *view,
+	struct wlr_box target, struct output *output,
+	edge_validator_t validator, bool use_pending);
+
+void edges_find_outputs(struct border *nearest_edges, struct view *view,
+	struct wlr_box target, struct output *output,
+	edge_validator_t validator, bool use_pending);
+
+void edges_adjust_move_coords(struct view *view, struct border edges,
+	int *x, int *y, bool use_pending);
+
+void edges_adjust_resize_geom(struct view *view, struct border edges,
+	uint32_t resize_edges, struct wlr_box *geom, bool use_pending);
+
+#endif /* LABWC_EDGES_H */