From 5ea617a39353c5a2dd9089c76e7d2e3b9b7cd1b7 Mon Sep 17 00:00:00 2001
From: John Lindgren <john@jlindgren.net>
Date: Tue, 25 Nov 2025 23:25:47 -0500
Subject: [PATCH] box: factor out box_center()

---
 include/common/box.h | 11 +++++++++++
 src/common/box.c     | 19 +++++++++++++++++++
 src/view.c           | 18 +-----------------
 3 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/include/common/box.h b/include/common/box.h
index 45c0fc4d..9f18b45e 100644
--- a/include/common/box.h
+++ b/include/common/box.h
@@ -10,6 +10,17 @@ bool box_intersects(struct wlr_box *box_a, struct wlr_box *box_b);
 void box_union(struct wlr_box *box_dest, struct wlr_box *box_a,
 	struct wlr_box *box_b);
 
+/*
+ * Centers a content box (width & height) within a reference box,
+ * limiting it (if possible) to not extend outside a bounding box.
+ *
+ * The reference box and bounding box are often the same but could be
+ * different (e.g. when centering a view within its parent but limiting
+ * to usable output area).
+ */
+void box_center(int width, int height, const struct wlr_box *ref,
+	const struct wlr_box *bound, int *x, int *y);
+
 /*
  * Fits and centers a content box (width & height) within a bounding box.
  * The content box is downscaled if necessary (preserving aspect ratio) but
diff --git a/src/common/box.c b/src/common/box.c
index 2520f733..5cc91bf3 100644
--- a/src/common/box.c
+++ b/src/common/box.c
@@ -35,6 +35,25 @@ box_union(struct wlr_box *box_dest, struct wlr_box *box_a, struct wlr_box *box_b
 	box_dest->height = y2 - y1;
 }
 
+void
+box_center(int width, int height, const struct wlr_box *ref,
+		const struct wlr_box *bound, int *x, int *y)
+{
+	*x = ref->x + (ref->width - width) / 2;
+	*y = ref->y + (ref->height - height) / 2;
+
+	if (*x < bound->x) {
+		*x = bound->x;
+	} else if (*x + width > bound->x + bound->width) {
+		*x = bound->x + bound->width - width;
+	}
+	if (*y < bound->y) {
+		*y = bound->y;
+	} else if (*y + height > bound->y + bound->height) {
+		*y = bound->y + bound->height - height;
+	}
+}
+
 struct wlr_box
 box_fit_within(int width, int height, struct wlr_box *bound)
 {
diff --git a/src/view.c b/src/view.c
index cc16536f..57014b8d 100644
--- a/src/view.c
+++ b/src/view.c
@@ -816,23 +816,7 @@ view_compute_centered_position(struct view *view, const struct wlr_box *ref,
 	int height = h + margin.top + margin.bottom;
 
 	/* If reference box is NULL then center to usable area */
-	if (!ref) {
-		ref = &usable;
-	}
-	*x = ref->x + (ref->width - width) / 2;
-	*y = ref->y + (ref->height - height) / 2;
-
-	/* Fit the view within the usable area */
-	if (*x < usable.x) {
-		*x = usable.x;
-	} else if (*x + width > usable.x + usable.width) {
-		*x = usable.x + usable.width - width;
-	}
-	if (*y < usable.y) {
-		*y = usable.y;
-	} else if (*y + height > usable.y + usable.height) {
-		*y = usable.y + usable.height - height;
-	}
+	box_center(width, height, ref ? ref : &usable, &usable, x, y);
 
 	*x += margin.left;
 	*y += margin.top;