polygonal lasso

1 files changed, 33 insertions, 0 deletions

diff --git a/assets/javascripts/util/coords.js b/assets/javascripts/util/coords.js
new file mode 100644
index 0000000..74b7fda
--- /dev/null
+++ b/assets/javascripts/util/coords.js
@@ -0,0 +1,33 @@
+function offsetFromPoint(event, element) {
+  function a(width) {
+    var l = 0, r = 200;
+    while (r - l > 0.0001) {
+      var mid = (r + l) / 2;
+      var a = document.createElement('div');
+      a.style.cssText = 'position: absolute;left:0;top:0;background: red;z-index: 1000;';
+      a.style[width ? 'width' : 'height'] = mid.toFixed(3) + '%';
+      a.style[width ? 'height' : 'width'] = '100%';
+      element.appendChild(a);
+      var x = document.elementFromPoint(event.clientX, event.clientY);
+      element.removeChild(a);
+      if (x === a) {
+        r = mid;
+      } else {
+        if (r === 200) {
+          return null;
+        }
+        l = mid;
+      }
+    }
+    return mid;
+  }
+  var l = a(1), 
+      t = a(0);
+  return l && t ? {
+    left: l / 100,
+    top: t / 100,
+    toString: function () {
+      return 'left: ' + l + '%, top: ' + t + '%';
+    }
+  } : null;
+}