feat(DraggableCore): apply scale property while dragging an element

lib/DraggableCore.js

@@ -67,6 +67,7 @@ export type DraggableCoreProps = {
   onDrag: DraggableEventHandler,
   onStop: DraggableEventHandler,
   onMouseDown: (e: MouseEvent) => void,
+  scale: number,
 };
 
 //
@@ -185,6 +186,11 @@ export default class DraggableCore extends React.Component<DraggableCoreProps, D
      */
     onMouseDown: PropTypes.func,
 
+    /**
+     * `scale`, if set, applies scaling while dragging an element
+     */
+    scale: PropTypes.number,
+
     /**
      * These properties should be defined on the child, not here.
      */
@@ -206,6 +212,7 @@ export default class DraggableCore extends React.Component<DraggableCoreProps, D
     onDrag: function(){},
     onStop: function(){},
     onMouseDown: function(){},
+    scale: 1,
   };
 
   state = {

lib/utils/domFns.js

@@ -99,12 +99,12 @@ export function innerWidth(node: HTMLElement): number {
 }
 
 // Get from offsetParent
-export function offsetXYFromParent(evt: {clientX: number, clientY: number}, offsetParent: HTMLElement): ControlPosition {
+export function offsetXYFromParent(evt: {clientX: number, clientY: number}, offsetParent: HTMLElement, scale: number): ControlPosition {
   const isBody = offsetParent === offsetParent.ownerDocument.body;
   const offsetParentRect = isBody ? {left: 0, top: 0} : offsetParent.getBoundingClientRect();
 
-  const x = evt.clientX + offsetParent.scrollLeft - offsetParentRect.left;
-  const y = evt.clientY + offsetParent.scrollTop - offsetParentRect.top;
+  const x = (evt.clientX + offsetParent.scrollLeft - offsetParentRect.left) / scale;
+  const y = (evt.clientY + offsetParent.scrollTop - offsetParentRect.top) / scale;
 
   return {x, y};
 }

lib/utils/positionFns.js

@@ -73,7 +73,7 @@ export function getControlPosition(e: MouseTouchEvent, touchIdentifier: ?number,
   const node = findDOMNode(draggableCore);
   // User can provide an offsetParent if desired.
   const offsetParent = draggableCore.props.offsetParent || node.offsetParent || node.ownerDocument.body;
-  return offsetXYFromParent(touchObj || e, offsetParent);
+  return offsetXYFromParent(touchObj || e, offsetParent, draggableCore.props.scale);
 }
 
 // Create an data object exposed by <DraggableCore>'s events

specs/draggable.spec.jsx

@@ -683,6 +683,44 @@ describe('react-draggable', function () {
 
       simulateMovementFromTo(drag, 200, 200, 300, 300);
     });
+
+    it('should call back with correct position when parent element is 2x scaled', function() {
+      function onDrag(event, data) {
+        // visually it will look like 100, because parent is 2x scaled
+        assert(data.x === 50);
+        assert(data.y === 50);
+        assert(data.deltaX === 50);
+        assert(data.deltaY === 50);
+        assert(data.node === ReactDOM.findDOMNode(drag));
+      }
+      drag = TestUtils.renderIntoDocument(
+        <Draggable onDrag={onDrag} scale={2}>
+          <div />
+        </Draggable>
+      );
+
+      // (element, fromX, fromY, toX, toY)
+      simulateMovementFromTo(drag, 0, 0, 100, 100);
+    });
+
+    it('should call back with correct position when parent element is 0.5x scaled', function() {
+      function onDrag(event, data) {
+        // visually it will look like 100, because parent is 0.5x scaled
+        assert(data.x === 200);
+        assert(data.y === 200);
+        assert(data.deltaX === 200);
+        assert(data.deltaY === 200);
+        assert(data.node === ReactDOM.findDOMNode(drag));
+      }
+      drag = TestUtils.renderIntoDocument(
+        <Draggable onDrag={onDrag} scale={0.5}>
+          <div />
+        </Draggable>
+      );
+
+      // (element, fromX, fromY, toX, toY)
+      simulateMovementFromTo(drag, 0, 0, 100, 100);
+    });
   });
 
   describe('DraggableCore callbacks', function () {
@@ -703,6 +741,44 @@ describe('react-draggable', function () {
       // (element, fromX, fromY, toX, toY)
       simulateMovementFromTo(drag, 0, 0, 100, 100);
     });
+
+    it('should call back with correct position when parent element is 2x scaled', function() {
+      function onDrag(event, data) {
+        // visually it will look like 100, because parent is 2x scaled
+        assert(data.x === 50);
+        assert(data.y === 50);
+        assert(data.deltaX === 50);
+        assert(data.deltaY === 50);
+        assert(data.node === ReactDOM.findDOMNode(drag));
+      }
+      drag = TestUtils.renderIntoDocument(
+        <DraggableCore onDrag={onDrag} scale={2}>
+          <div />
+        </DraggableCore>
+      );
+
+      // (element, fromX, fromY, toX, toY)
+      simulateMovementFromTo(drag, 0, 0, 100, 100);
+    });
+
+    it('should call back with correct position when parent element is 0.5x scaled', function() {
+      function onDrag(event, data) {
+        // visually it will look like 100, because parent is  0.5x scaled
+        assert(data.x === 200);
+        assert(data.y === 200);
+        assert(data.deltaX === 200);
+        assert(data.deltaY === 200);
+        assert(data.node === ReactDOM.findDOMNode(drag));
+      }
+      drag = TestUtils.renderIntoDocument(
+        <DraggableCore onDrag={onDrag} scale={0.5}>
+          <div />
+        </DraggableCore>
+      );
+
+      // (element, fromX, fromY, toX, toY)
+      simulateMovementFromTo(drag, 0, 0, 100, 100);
+    });
   });