2 files changed, 99 insertions, 0 deletions

diff --git a/src/RectangleUtil.hh b/src/RectangleUtil.hh
index 88c3a33..9725e63 100644
--- a/src/RectangleUtil.hh
+++ b/src/RectangleUtil.hh
@@ -24,6 +24,50 @@ bool insideBorder(const RectangleLike& rect,
         y < rect.y() + (int)rect.height() + border_width;
 }
 
+
+
+/*
+ * Determines if rectangle 'a' overlaps rectangle 'b'
+ * @returns true if 'a' overlaps 'b'
+ *
+ *    outside              overlap situations
+ *
+ *  a----a            a----a         a--------a  b--------b
+ *  |    | b----b     |  b-+--b      | b----b |  | a----a |
+ *  a----a |    |     a--+-a  |      | |    | |  | |    | |
+ *         b----b        b----b      | b----b |  | a----a |
+ *                                   a--------a  b--------b
+ *
+ */
+
+inline bool overlapRectangles(
+        int ax, int ay, int awidth, int aheight,
+        int bx, int by, int bwidth, int bheight) {
+
+    bool do_not_overlap =
+         ax > (bx + bwidth)
+      || bx > (ax + awidth)
+      || ay > (by + bheight)
+      || by > (ay + aheight);
+
+    return !do_not_overlap;
+}
+
+
+/*
+ * Determines if rectangle 'a' overlaps rectangle 'b'
+ * @param a - rectangle a
+ * @param b - rectangle b
+ * @returns true if 'a' overlaps 'b'
+ */
+template <typename RectangleLikeA, typename RectangleLikeB>
+bool overlapRectangles(const RectangleLikeA& a, const RectangleLikeB& b) {
+
+    return overlapRectangles(
+            a.x(), a.y(), a.width(), a.height(),
+            b.x(), b.y(), b.width(), b.height());
+}
+
 } // namespace RectangleUtil
 
 
diff --git a/src/tests/testRectangleUtil.cc b/src/tests/testRectangleUtil.cc
index f10b6af..2da2a4e 100644
--- a/src/tests/testRectangleUtil.cc
+++ b/src/tests/testRectangleUtil.cc
@@ -55,12 +55,67 @@ int test_insideBorder() {
     return 0;
 }
 
+int test_overlapRectangles() {
 
+    printf("testing RectangleUtil::overlapRectangles()\n");
+
+    struct _t {
+        struct Rect a;
+        struct Rect b;
+        int truth;
+    };
+
+    struct _test {
+        bool operator()(const Rect& a, const Rect& b, int truth, int i) {
+
+            int result = RectangleUtil::overlapRectangles(a, b);
+
+            printf("  %d: [%2d %2d]-[%2d %2d] %s [%2d %2d]-[%2d %2d]: %s\n",
+                    i,
+                    a.x(), a.y(),
+                    a.x() + (int)a.width(),
+                    a.y() + (int)a.height(),
+                    result ? "overlaps" : "does not overlap",
+                    b.x(), b.y(),
+                    b.x() + (int)b.width(),
+                    b.y() + (int)b.height(),
+                    result == truth ? "ok" : "failed");
+            return result == truth;
+        }
+    };
+
+    const _t tests[] = {
+
+        { { 0, 0, 8, 8 }, {  0, 0, 8, 8 }, true  }, // b equals a
+        { { 0, 0, 8, 8 }, {  3, 3, 3, 3 }, true  }, // b completely inside a
+        { { 0, 0, 8, 8 }, {  4, 4, 8, 8 }, true  }, // b overlaps a in one corner
+        { { 0, 0, 8, 8 }, {  4,-1, 2, 9 }, true  }, // b overlaps a in the middle
+
+        { { 0, 0, 8, 8 }, { -8, 0, 5, 8 }, false }, // b completely left from a
+        { { 0, 0, 8, 8 }, {  9, 0, 5, 8 }, false }, // b completely right from a
+        { { 0, 0, 8, 8 }, {  0,-9, 5, 8 }, false }, // b completely down below a
+        { { 0, 0, 8, 8 }, {  0, 9, 5, 8 }, false }, // b completely up above a
+    };
+
+
+
+    _test test;
+    int i;
+    for (i = 0; i < sizeof(tests)/sizeof(_t); ++i) {
+        test(tests[i].a, tests[i].b, tests[i].truth, i);
+        test(tests[i].b, tests[i].a, tests[i].truth, i);
+    }
+
+    printf("done.\n");
+
+    return 0;
+}
 
 
 int main(int argc, char **argv) {
 
     test_insideBorder();
+    test_overlapRectangles();
 
     return 0;
 }