chore(dragging): normalize coordinates to full pixels

This ensures dragging emits events with full pixel coordinates only, as
we don't support sub-pixel positioning
anywhere anyway.

Closes #271

lib/features/dragging/Dragging.js

@@ -143,8 +143,8 @@ export default function Dragging(eventBus, canvas, selection) {
     var clientRect = canvas._container.getBoundingClientRect();
 
     return {
-      x: viewbox.x + round((globalPosition.x - clientRect.left) / viewbox.scale),
-      y: viewbox.y + round((globalPosition.y - clientRect.top) / viewbox.scale)
+      x: viewbox.x + (globalPosition.x - clientRect.left) / viewbox.scale,
+      y: viewbox.y + (globalPosition.y - clientRect.top) / viewbox.scale
     };
   }
 
@@ -184,15 +184,16 @@ export default function Dragging(eventBus, canvas, selection) {
         localCurrent = toLocalPoint(globalCurrent),
         localDelta = deltaPos(localCurrent, localStart);
 
+
     // activate context explicitly or once threshold is reached
     if (!context.active && (activate || getLength(globalDelta) > context.threshold)) {
 
       // fire start event with original
       // starting coordinates
 
       assign(payload, {
-        x: localStart.x + displacement.x,
-        y: localStart.y + displacement.y,
+        x: round(localStart.x + displacement.x),
+        y: round(localStart.y + displacement.y),
         dx: 0,
         dy: 0
       }, { originalEvent: event });
@@ -226,10 +227,10 @@ export default function Dragging(eventBus, canvas, selection) {
 
       // update payload with actual coordinates
       assign(payload, {
-        x: localCurrent.x + displacement.x,
-        y: localCurrent.y + displacement.y,
-        dx: localDelta.x,
-        dy: localDelta.y
+        x: round(localCurrent.x + displacement.x),
+        y: round(localCurrent.y + displacement.y),
+        dx: round(localDelta.x),
+        dy: round(localDelta.y)
       }, { originalEvent: event });
 
       // emit move event

test/spec/features/dragging/DraggingSpec.js

@@ -303,6 +303,37 @@ describe('features/dragging - Dragging', function() {
       ]);
     }));
 
+
+    it('should normalize to full pixel coordinates', inject(
+      function(dragging, canvas) {
+
+        // given
+        canvas.zoom(0.37);
+
+        // assume viewbox has sub-pixel x coordinate
+        expect(canvas.viewbox().x).not.to.eql(Math.round(canvas.viewbox().x));
+        expect(canvas.viewbox().y).not.to.eql(Math.round(canvas.viewbox().y));
+
+        var events = recordEvents('foo');
+
+        // when
+        dragging.init(canvasEvent({ x: 0, y: 0 }), { x: 10.12321312, y: 9.9123821 }, 'foo');
+        dragging.move(canvasEvent({ x: 20, y: 10 }));
+
+        dragging.cancel();
+
+        // then
+        expect(events.map(raw)).to.eql([
+          { type: 'foo.init' },
+          { x: 10, y: 10, dx: 0, dy: 0, type: 'foo.start' },
+          { x: 64, y: 37, dx: 54, dy: 27, type: 'foo.move' },
+          { x: 64, y: 37, dx: 54, dy: 27, type: 'foo.cancel' },
+          { x: 64, y: 37, dx: 54, dy: 27, type: 'foo.cleanup' },
+          { x: 64, y: 37, dx: 54, dy: 27, type: 'foo.canceled' }
+        ]);
+      }
+    ));
+
   });
 
 });