From 9fd2d7bdaf24a3984e6ad129e0c7afacd6a9ebd4 Mon Sep 17 00:00:00 2001
From: Matthias Kruk <m@m10k.eu>
Date: Wed, 19 May 2021 08:23:05 +0900
Subject: [PATCH] common: Add functions for comparing geoms and pointers

The loop_find() function needs a fallback comparison function to use
if no other comparison function was provided. This commit adds a
comparison function that compares two pointers.
Further, this commit adds a function that calculates the intersecting
area of two geometries.
---
 common.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 common.h | 10 ++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 common.c

diff --git a/common.c b/common.c
new file mode 100644
index 0000000..2c6058d
--- /dev/null
+++ b/common.c
@@ -0,0 +1,56 @@
+#include "common.h"
+
+#ifndef MIN
+#define MIN(X,Y) ((X) < (Y) ? (X) : (Y))
+#endif /* !defined(MIN) */
+
+#ifndef MAX
+#define MAX(X,Y) ((X) > (Y) ? (X) : (Y))
+#endif /* !defined(MAX) */
+
+int cmp_pointer(void *left, void *right)
+{
+	return(left == right);
+}
+
+int geom_intersects(struct geom *first, struct geom *second)
+{
+	int top;
+	int bottom;
+	int left;
+	int right;
+	int width;
+	int height;
+
+	/*
+	 *           left
+	 *           |   right
+	 *           |   |
+	 *           v   v
+	 *    +----------+
+	 *    |          |
+	 *    |      +---+------+ <-- top
+	 *    |      |   |      |
+	 *    +------+---+      | <-- bottom
+	 *           |          |
+	 *           +----------+
+	 *
+	 * This function calculated the area of the intersection of
+	 * the two rectangles. If the area is zero, the rectangles
+	 * do not intersect.
+	 */
+
+	top    = MAX(first->y,
+		     second->y);
+	bottom = MIN(first->y  + first->h,
+		     second->y + second->h);
+	left   = MAX(first->x,
+		     second->x);
+	right  = MIN(first->x  + first->w,
+		     second->x + second->w);
+
+	width  = MAX(0, right - left);
+	height = MAX(0, bottom - top);
+
+	return(width * height);
+}
diff --git a/common.h b/common.h
index 3bb5368..e041a23 100644
--- a/common.h
+++ b/common.h
@@ -8,4 +8,14 @@ struct geom {
 	unsigned int h;
 };
 
+#ifndef FALSE
+#define FALSE 0
+#endif
+#ifndef TRUE
+#define TRUE  (!FALSE)
+#endif
+
+int cmp_pointer(void *left, void *right);
+int geom_intersects(struct geom *left, struct geom *right);
+
 #endif /* COMMON_H */
-- 
2.47.3