feat(snapGrid): implement draggable snap grids

Closes #4

Author: Matt Lewis

demo/demo.component.ts

@@ -6,8 +6,8 @@ import {Component} from '@angular/core';
     <div mwlDraggable dropData="foo">
       Drag me!
     </div>
-    <div mwlDraggable dropData="bar">
-      Or drag me!
+    <div mwlDraggable dropData="bar" [snapGrid]="{x: 100, y: 100}">
+      I snap to a 100x100 grid
     </div>
     <div
       [class.dropOverActive]="dropOverActive"

src/draggable.directive.ts

@@ -12,6 +12,8 @@ type Coordinates = {x: number, y: number};
 
 type DragAxis = {x: boolean, y: boolean};
 
+type SnapGrid = {x?: number, y?: number};
+
 @Directive({
   selector: '[mwlDraggable]'
 })
@@ -21,6 +23,8 @@ export class Draggable implements OnInit, OnDestroy {
 
   @Input() dragAxis: DragAxis = {x: true, y: true};
 
+  @Input() snapGrid: SnapGrid = {};
+
   @Output() dragStart: EventEmitter<Coordinates> = new EventEmitter<Coordinates>();
 
   @Output() dragging: EventEmitter<Coordinates> = new EventEmitter<Coordinates>();
@@ -58,12 +62,27 @@ export class Draggable implements OnInit, OnDestroy {
 
         })
         .map((moveData: Coordinates) => {
+
+          if (this.snapGrid.x) {
+            moveData.x = Math.floor(moveData.x / this.snapGrid.x) * this.snapGrid.x;
+          }
+
+          if (this.snapGrid.y) {
+            moveData.y = Math.floor(moveData.y / this.snapGrid.y) * this.snapGrid.y;
+          }
+
+          return moveData;
+        })
+        .map((moveData: Coordinates) => {
+
           if (!this.dragAxis.x) {
             moveData.x = 0;
           }
+
           if (!this.dragAxis.y) {
             moveData.y = 0;
           }
+
           return moveData;
         })
         .takeUntil(Observable.merge(this.mouseUp, this.mouseDown));

test/draggable.directive.spec.ts

@@ -13,6 +13,7 @@ describe('draggable directive', () => {
       <div 
         mwlDraggable
         [dragAxis]="dragAxis"
+        [snapGrid]="snapGrid"
         (dragStart)="dragStart($event)" 
         (dragging)="dragging($event)"
         (dragEnd)="dragEnd($event)">
@@ -26,6 +27,7 @@ describe('draggable directive', () => {
     public dragging: sinon.SinonSpy = sinon.spy();
     public dragEnd: sinon.SinonSpy = sinon.spy();
     public dragAxis: any = {x: true, y: true};
+    public snapGrid: any = {};
 
   }
 
@@ -118,4 +120,38 @@ describe('draggable directive', () => {
     expect(fixture.componentInstance.dragEnd).to.have.been.calledWith({x: 0, y: 0});
   });
 
+  it('should snap all horizontal drags to a grid', () => {
+    fixture.componentInstance.snapGrid = {x: 10};
+    fixture.detectChanges();
+    const draggableElement: HTMLElement = fixture.componentInstance.draggable.element.nativeElement;
+    triggerDomEvent('mousedown', draggableElement, {clientX: 5, clientY: 10});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 7, clientY: 12});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 0, y: 2});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 14, clientY: 18});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 0, y: 8});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 15, clientY: 20});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 10, y: 10});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 16, clientY: 22});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 10, y: 12});
+    triggerDomEvent('mouseup', draggableElement, {clientX: 16, clientY: 22});
+    expect(fixture.componentInstance.dragEnd).to.have.been.calledWith({x: 10, y: 12});
+  });
+
+  it('should snap all vertical drags to a grid', () => {
+    fixture.componentInstance.snapGrid = {y: 10};
+    fixture.detectChanges();
+    const draggableElement: HTMLElement = fixture.componentInstance.draggable.element.nativeElement;
+    triggerDomEvent('mousedown', draggableElement, {clientX: 10, clientY: 5});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 12, clientY: 7});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 2, y: 0});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 18, clientY: 14});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 8, y: 0});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 20, clientY: 15});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 10, y: 10});
+    triggerDomEvent('mousemove', draggableElement, {clientX: 22, clientY: 16});
+    expect(fixture.componentInstance.dragging).to.have.been.calledWith({x: 12, y: 10});
+    triggerDomEvent('mouseup', draggableElement, {clientX: 22, clientY: 16});
+    expect(fixture.componentInstance.dragEnd).to.have.been.calledWith({x: 12, y: 10});
+  });
+
 });