fix(drag-drop): dragged elements blurry in some browsers (#14299)

Rounds the `transform` value before they're assigned, in order to avoid blurriness in some browsers.

Fixes #14283.

Author: crisbeto

src/cdk/drag-drop/drag.spec.ts

@@ -504,6 +504,7 @@ describe('CdkDrag', () => {
       expect(dragElement.style.touchAction)
         .not.toEqual('none', 'should not disable touchAction on when there is a drag handle');
     });
+
     it('should be able to reset a freely-dragged item to its initial position', fakeAsync(() => {
       const fixture = createComponent(StandaloneDraggable);
       fixture.detectChanges();
@@ -556,7 +557,17 @@ describe('CdkDrag', () => {
         expect(fixture.componentInstance.endedSpy).toHaveBeenCalledTimes(1);
       }));
 
-    });
+    it('should round the transform value', fakeAsync(() => {
+      const fixture = createComponent(StandaloneDraggable);
+      fixture.detectChanges();
+      const dragElement = fixture.componentInstance.dragElement.nativeElement;
+
+      expect(dragElement.style.transform).toBeFalsy();
+      dragElementViaMouse(fixture, dragElement, 13.37, 37);
+      expect(dragElement.style.transform).toBe('translate3d(13px, 37px, 0px)');
+    }));
+
+  });
 
   describe('draggable with a handle', () => {
     it('should not be able to drag the entire element if it has a handle', fakeAsync(() => {

src/cdk/drag-drop/drag.ts

@@ -866,7 +866,9 @@ interface Point {
  * @param y Desired position of the element along the Y axis.
  */
 function getTransform(x: number, y: number): string {
-  return `translate3d(${x}px, ${y}px, 0)`;
+  // Round the transforms since some browsers will
+  // blur the elements, for sub-pixel transforms.
+  return `translate3d(${Math.round(x)}px, ${Math.round(y)}px, 0)`;
 }
 
 /** Creates a deep clone of an element. */

src/cdk/drag-drop/drop-list.ts

@@ -362,10 +362,12 @@ export class CdkDropList<T = any> implements OnInit, OnDestroy {
       // Note that we shouldn't use `getBoundingClientRect` here to update the cache, because the
       // elements may be mid-animation which will give us a wrong result.
       if (isHorizontal) {
-        elementToOffset.style.transform = `translate3d(${sibling.offset}px, 0, 0)`;
+        // Round the transforms since some browsers will
+        // blur the elements, for sub-pixel transforms.
+        elementToOffset.style.transform = `translate3d(${Math.round(sibling.offset)}px, 0, 0)`;
         this._adjustClientRect(sibling.clientRect, 0, offset);
       } else {
-        elementToOffset.style.transform = `translate3d(0, ${sibling.offset}px, 0)`;
+        elementToOffset.style.transform = `translate3d(0, ${Math.round(sibling.offset)}px, 0)`;
         this._adjustClientRect(sibling.clientRect, offset, 0);
       }
     });