diff -r ed9b16b33628 -r 83adf8859c55 svghmi/bbox_intersect.ysl2
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/svghmi/bbox_intersect.ysl2	Mon Mar 16 18:27:49 2020 +0100
@@ -0,0 +1,120 @@
+// bbox_intersect.ysl2
+//
+// bounding boxes intersection tests
+
+// Rates 1D intersection of 2 segments A and B
+// described respectively with a0,a1 and b0,b1
+def "func:intersect_1d" {
+    // it is assumed that a1 > a0 and b1 > b0
+    param "a0";
+    param "a1";
+    param "b0";
+    param "b1";
+
+    const "d0", "$a0 >= $b0";
+    const "d1", "$a1 >= $b1";
+    choose {
+        when "not($d0) and $d1"
+            // b contained in a
+            //   a0<b0 b1<a1
+            // a +--------+
+            // b    +--+
+            result "3";
+        when "$d0 and not($d1)"
+            // a contained in b
+            //   b0<a0 a1<b1
+            // a    +--+
+            // b +--------+
+            result "2";
+        when "$d0 and $d1 and $a0 < $b1"
+            // a and b are overlapped 
+            //   b0<a0<b1<a1
+            // a    +-----+
+            // b +-----+
+            result "1";
+        when "not($d0) and not($d1) and $b0 < $a1"
+            // a and b are overlapped
+            //   a0<b0<a1<b1
+            // a +-----+
+            // b    +-----+
+            result "1";
+            // since orientation doesn't matter,
+            // rated same as previous symetrical overlapping
+        otherwise
+            result "0"; /* no intersection*/
+    }
+}
+
+
+// Rates intersection A and B areas described with x,y,w and h 
+// attributes passed as $a and $b parameters.
+// 
+// returns :
+// 0 - no intersection
+//            .-----.
+//    .-----. |    b|
+//    |     | |     |
+//    |     | '-----'
+//    |a    |
+//    '-----'
+//
+// 1 - overlapping
+//        .-----.
+//    .---|--. b|
+//    |   |  |  |
+//    |   '-----'
+//    |a     |
+//    '------'
+//
+// 2 - overlapping
+//        .-----.
+//        |  a  |
+//    .---|-----|---.
+//    |   '-----'   |
+//    | b           |
+//    '-------------'
+//
+// 3 - overlapping
+//        .-----.
+//        |  b  |
+//    .---|-----|---.
+//    |   '-----'   |
+//    | a           |
+//    '-------------'
+//
+// 4 - a contained in b
+//    .-------------.
+//    |   .-----.   |
+//    |   |  a  |   |
+//    |b  '-----'   |
+//    '-------------'
+//
+// 6 - overlapping
+//        .----.
+//        |   b|
+//    .---|----|---.
+//    |a  |    |   |
+//    '---|----|---'
+//        '----'
+//
+// 9 - b contained in a
+//    .-------------.
+//    |   .-----.   |
+//    |   |  b  |   |
+//    |a  '-----'   |
+//    '-------------'
+//
+def "func:intersect" {
+    param "a";
+    param "b";
+
+    const "x_intersect", "func:intersect_1d($a/@x, $a/@x+$a/@w, $b/@x, $b/@x+$b/@w)";
+
+    choose{
+        when "$x_intersect != 0"{
+            const "y_intersect", "func:intersect_1d($a/@y, $a/@y+$a/@h, $b/@y, $b/@y+$b/@h)";
+            result "$x_intersect * $y_intersect";
+        }
+        otherwise result "0";
+    }
+}