From 22e50aa4e2f47e236c88fd1ec60f621b1ddda6ab Mon Sep 17 00:00:00 2001
From: John Lindgren <john@jlindgren.net>
Date: Sat, 5 Oct 2024 09:45:48 -0400
Subject: [PATCH] common/box: add box_fit_within()

Factor out common math from ssd's get_scale_box() for use elsewhere.
---
 include/common/box.h | 21 +++++++++++++++------
 src/common/box.c     | 26 ++++++++++++++++++++++++++
 src/ssd/ssd-part.c   | 27 +++++----------------------
 3 files changed, 46 insertions(+), 28 deletions(-)

diff --git a/include/common/box.h b/include/common/box.h
index 105ff297..651fcff0 100644
--- a/include/common/box.h
+++ b/include/common/box.h
@@ -4,14 +4,23 @@
 
 #include <wlr/util/box.h>
 
-bool
-box_contains(struct wlr_box *box_super, struct wlr_box *box_sub);
+bool box_contains(struct wlr_box *box_super, struct wlr_box *box_sub);
 
-bool
-box_intersects(struct wlr_box *box_a, struct wlr_box *box_b);
+bool box_intersects(struct wlr_box *box_a, struct wlr_box *box_b);
 
 /* Returns the bounding box of 2 boxes */
-void
-box_union(struct wlr_box *box_dest, 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);
+
+/*
+ * Fits and centers a content box (width & height) within a bounding box
+ * (max_width & max_height). The content box is downscaled if necessary
+ * (preserving aspect ratio) but not upscaled.
+ *
+ * The returned x & y coordinates are the centered content position
+ * relative to the top-left corner of the bounding box.
+ */
+struct wlr_box box_fit_within(int width, int height, int max_width,
+	int max_height);
 
 #endif /* LABWC_BOX_H */
diff --git a/src/common/box.c b/src/common/box.c
index 1a56cfe2..eefa535c 100644
--- a/src/common/box.c
+++ b/src/common/box.c
@@ -47,3 +47,29 @@ box_union(struct wlr_box *box_dest, struct wlr_box *box_a, struct wlr_box *box_b
 	box_dest->width = x2 - x1;
 	box_dest->height = y2 - y1;
 }
+
+struct wlr_box
+box_fit_within(int width, int height, int max_width, int max_height)
+{
+	struct wlr_box box;
+
+	if (width <= max_width && height <= max_height) {
+		/* No downscaling needed */
+		box.width = width;
+		box.height = height;
+	} else if (width * max_height > height * max_width) {
+		/* Wider content, fit width */
+		box.width = max_width;
+		box.height = (height * max_width + (width / 2)) / width;
+	} else {
+		/* Taller content, fit height */
+		box.width = (width * max_height + (height / 2)) / height;
+		box.height = max_height;
+	}
+
+	/* Compute centered position */
+	box.x = (max_width - box.width) / 2;
+	box.y = (max_height - box.height) / 2;
+
+	return box;
+}
diff --git a/src/ssd/ssd-part.c b/src/ssd/ssd-part.c
index 2e572966..58305e0c 100644
--- a/src/ssd/ssd-part.c
+++ b/src/ssd/ssd-part.c
@@ -2,6 +2,7 @@
 
 #include <assert.h>
 #include "buffer.h"
+#include "common/box.h"
 #include "common/list.h"
 #include "common/mem.h"
 #include "labwc.h"
@@ -80,29 +81,11 @@ add_scene_buffer(struct wl_list *list, enum ssd_part_type type,
 }
 
 static struct wlr_box
-get_scale_box(struct lab_data_buffer *buffer, double container_width,
-		double container_height)
+get_scale_box(struct lab_data_buffer *buffer, int container_width,
+		int container_height)
 {
-	struct wlr_box icon_geo = {
-		.width = buffer->logical_width,
-		.height = buffer->logical_height
-	};
-
-	/* Scale down buffer if required */
-	if (icon_geo.width && icon_geo.height) {
-		double scale = MIN(container_width / icon_geo.width,
-			container_height / icon_geo.height);
-		if (scale < 1.0f) {
-			icon_geo.width = (double)icon_geo.width * scale;
-			icon_geo.height = (double)icon_geo.height * scale;
-		}
-	}
-
-	/* Center buffer on both axis */
-	icon_geo.x = (container_width - icon_geo.width) / 2;
-	icon_geo.y = (container_height - icon_geo.height) / 2;
-
-	return icon_geo;
+	return box_fit_within(buffer->logical_width, buffer->logical_height,
+		container_width, container_height);
 }
 
 void
-- 
2.52.0