Add discrete steps and snapping to the slider

src/components/slider/slider.scss

@@ -31,6 +31,9 @@ $md-slider-disabled-color: rgba(black, 0.26);
 @mixin slider-thumb-position($width: $md-slider-thumb-size, $height: $md-slider-thumb-size) {
   position: absolute;
   top: center-vertically($md-slider-thickness, $height);
+  // This makes it so that the center of the thumb aligns with where the click was.
+  // This is not affected by the movement of the thumb.
+  left: (-$width / 2);
   width: $width;
   height: $height;
   border-radius: max($width, $height);

src/components/slider/slider.spec.ts

@@ -38,7 +38,6 @@ describe('MdSlider', () => {
     let sliderDimensions: ClientRect;
     let thumbElement: HTMLElement;
     let thumbDimensions: ClientRect;
-    let thumbWidth: number;
 
     beforeEach(async(() => {
       builder.createAsync(StandardSlider).then(f => {
@@ -56,8 +55,6 @@ describe('MdSlider', () => {
 
         thumbElement = <HTMLElement>sliderNativeElement.querySelector('.md-slider-thumb-position');
         thumbDimensions = thumbElement.getBoundingClientRect();
-        thumbWidth =
-            sliderNativeElement.querySelector('.md-slider-thumb').getBoundingClientRect().width;
       });
     }));
 
@@ -71,16 +68,14 @@ describe('MdSlider', () => {
       expect(sliderInstance.value).toBe(0);
       dispatchClickEvent(sliderTrackElement, 0.19);
       // The expected value is 19 from: percentage * difference of max and min.
-      let difference = Math.abs(sliderInstance.value - 19);
-      expect(difference).toBeLessThan(1);
+      expect(sliderInstance.value).toBe(19);
     });
 
     it('should update the value on a drag', () => {
       expect(sliderInstance.value).toBe(0);
       dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.89, gestureConfig);
       // The expected value is 89 from: percentage * difference of max and min.
-      let difference = Math.abs(sliderInstance.value - 89);
-      expect(difference).toBeLessThan(1);
+      expect(sliderInstance.value).toBe(89);
     });
 
     it('should set the value as min when dragging before the track', () => {
@@ -100,40 +95,49 @@ describe('MdSlider', () => {
       dispatchClickEvent(sliderTrackElement, 0.39);
 
       trackFillDimensions = trackFillElement.getBoundingClientRect();
-      // The fill should be close to the slider's width * the percentage from the click.
-      let difference = Math.abs(trackFillDimensions.width - (sliderDimensions.width * 0.39));
-      expect(difference).toBeLessThan(1);
+      thumbDimensions = thumbElement.getBoundingClientRect();
+
+      // The thumb and track fill positions are relative to the viewport, so to get the thumb's
+      // offset relative to the track, subtract the offset on the track fill.
+      let thumbPosition = thumbDimensions.left - trackFillDimensions.left;
+      // The track fill width should be equal to the thumb's position.
+      expect(Math.round(trackFillDimensions.width)).toBe(Math.round(thumbPosition));
     });
 
     it('should update the thumb position on click', () => {
-      expect(thumbDimensions.left).toBe(sliderDimensions.left - (thumbWidth / 2));
-      dispatchClickEvent(sliderTrackElement, 0.16);
+      expect(thumbDimensions.left).toBe(sliderDimensions.left);
+      // 50% is used here because the click event that is dispatched truncates the position and so
+      // a value had to be used that would not be truncated.
+      dispatchClickEvent(sliderTrackElement, 0.5);
 
       thumbDimensions = thumbElement.getBoundingClientRect();
-      // The thumb's offset is expected to be equal to the slider's offset + 0.16 * the slider's
-      // width - half the thumb width (to center the thumb).
-      let offset = sliderDimensions.left + (sliderDimensions.width * 0.16) - (thumbWidth / 2);
-      let difference = Math.abs(thumbDimensions.left - offset);
-      expect(difference).toBeLessThan(1);
+      // The thumb position should be at 50% of the slider's width + the offset of the slider.
+      // Both the thumb and the slider are affected by this offset.
+      expect(thumbDimensions.left).toBe(sliderDimensions.width * 0.5 + sliderDimensions.left);
     });
 
     it('should update the track fill on drag', () => {
       expect(trackFillDimensions.width).toBe(0);
       dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.86, gestureConfig);
 
       trackFillDimensions = trackFillElement.getBoundingClientRect();
-      let difference = Math.abs(trackFillDimensions.width - (sliderDimensions.width * 0.86));
-      expect(difference).toBeLessThan(1);
+      thumbDimensions = thumbElement.getBoundingClientRect();
+
+      // The thumb and track fill positions are relative to the viewport, so to get the thumb's
+      // offset relative to the track, subtract the offset on the track fill.
+      let thumbPosition = thumbDimensions.left - trackFillDimensions.left;
+      // The track fill width should be equal to the thumb's position.
+      expect(Math.round(trackFillDimensions.width)).toBe(Math.round(thumbPosition));
     });
 
     it('should update the thumb position on drag', () => {
-      expect(thumbDimensions.left).toBe(sliderDimensions.left - (thumbWidth / 2));
-      dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.27, gestureConfig);
+      expect(thumbDimensions.left).toBe(sliderDimensions.left);
+      // The drag event also truncates the position passed in, so 50% is used here as well to
+      // ensure the ability to calculate the expected position.
+      dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.5, gestureConfig);
 
       thumbDimensions = thumbElement.getBoundingClientRect();
-      let offset = sliderDimensions.left + (sliderDimensions.width * 0.27) - (thumbWidth / 2);
-      let difference = Math.abs(thumbDimensions.left - offset);
-      expect(difference).toBeLessThan(1);
+      expect(thumbDimensions.left).toBe(sliderDimensions.width * 0.5 + sliderDimensions.left);
     });
 
     it('should add the md-slider-active class on click', () => {
@@ -237,6 +241,9 @@ describe('MdSlider', () => {
     let sliderNativeElement: HTMLElement;
     let sliderInstance: MdSlider;
     let sliderTrackElement: HTMLElement;
+    let sliderDimensions: ClientRect;
+    let trackFillElement: HTMLElement;
+    let thumbElement: HTMLElement;
 
     beforeEach(async(() => {
       builder.createAsync(SliderWithMinAndMax).then(f => {
@@ -247,31 +254,62 @@ describe('MdSlider', () => {
         sliderNativeElement = sliderDebugElement.nativeElement;
         sliderInstance = sliderDebugElement.injector.get(MdSlider);
         sliderTrackElement = <HTMLElement>sliderNativeElement.querySelector('.md-slider-track');
+        sliderDimensions = sliderTrackElement.getBoundingClientRect();
+        trackFillElement = <HTMLElement>sliderNativeElement.querySelector('.md-slider-track-fill');
+        thumbElement = <HTMLElement>sliderNativeElement.querySelector('.md-slider-thumb-position');
       });
     }));
 
     it('should set the default values from the attributes', () => {
-      expect(sliderInstance.value).toBe(5);
-      expect(sliderInstance.min).toBe(5);
-      expect(sliderInstance.max).toBe(15);
+      expect(sliderInstance.value).toBe(4);
+      expect(sliderInstance.min).toBe(4);
+      expect(sliderInstance.max).toBe(6);
     });
 
     it('should set the correct value on click', () => {
       dispatchClickEvent(sliderTrackElement, 0.09);
       // Computed by multiplying the difference between the min and the max by the percentage from
       // the click and adding that to the minimum.
-      let value = 5 + (0.09 * (15 - 5));
-      let difference = Math.abs(sliderInstance.value - value);
-      expect(difference).toBeLessThan(1);
+      let value = Math.round(4 + (0.09 * (6 - 4)));
+      expect(sliderInstance.value).toBe(value);
     });
 
     it('should set the correct value on drag', () => {
       dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.62, gestureConfig);
       // Computed by multiplying the difference between the min and the max by the percentage from
       // the click and adding that to the minimum.
-      let value = 5 + (0.62 * (15 - 5));
-      let difference = Math.abs(sliderInstance.value - value);
-      expect(difference).toBeLessThan(1);
+      let value = Math.round(4 + (0.62 * (6 - 4)));
+      expect(sliderInstance.value).toBe(value);
+    });
+
+    it('should snap the thumb and fill to the nearest value on click', () => {
+      dispatchClickEvent(sliderTrackElement, 0.68);
+      fixture.detectChanges();
+
+      let trackFillDimensions = trackFillElement.getBoundingClientRect();
+      let thumbDimensions = thumbElement.getBoundingClientRect();
+      let thumbPosition = thumbDimensions.left - trackFillDimensions.left;
+
+      // The closest snap is halfway on the slider.
+      expect(thumbDimensions.left).toBe(sliderDimensions.width * 0.5 + sliderDimensions.left);
+      expect(Math.round(trackFillDimensions.width)).toBe(Math.round(thumbPosition));
+    });
+
+    it('should snap the thumb and fill to the nearest value on drag', () => {
+      dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.74, gestureConfig);
+      fixture.detectChanges();
+
+      dispatchDragEndEvent(sliderNativeElement, 0.74, gestureConfig);
+      fixture.detectChanges();
+
+      let trackFillDimensions = trackFillElement.getBoundingClientRect();
+      let thumbDimensions = thumbElement.getBoundingClientRect();
+      let thumbPosition = thumbDimensions.left - trackFillDimensions.left;
+
+      // The closest snap is at the halfway point on the slider.
+      expect(thumbDimensions.left).toBe(sliderDimensions.left + sliderDimensions.width * 0.5);
+      expect(Math.round(trackFillDimensions.width)).toBe(Math.round(thumbPosition));
+
     });
   });
 
@@ -302,16 +340,85 @@ describe('MdSlider', () => {
       dispatchClickEvent(sliderTrackElement, 0.92);
       // On a slider with default max and min the value should be approximately equal to the
       // percentage clicked. This should be the case regardless of what the original set value was.
-      let value = 92;
-      let difference = Math.abs(sliderInstance.value - value);
-      expect(difference).toBeLessThan(1);
+      expect(sliderInstance.value).toBe(92);
     });
 
     it('should set the correct value on drag', () => {
       dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.32, gestureConfig);
       expect(sliderInstance.value).toBe(32);
     });
   });
+
+  describe('slider with set step', () => {
+    let fixture: ComponentFixture<SliderWithStep>;
+    let sliderDebugElement: DebugElement;
+    let sliderNativeElement: HTMLElement;
+    let sliderInstance: MdSlider;
+    let sliderTrackElement: HTMLElement;
+    let sliderDimensions: ClientRect;
+    let trackFillElement: HTMLElement;
+    let thumbElement: HTMLElement;
+
+    beforeEach(async(() => {
+      builder.createAsync(SliderWithStep).then(f => {
+        fixture = f;
+        fixture.detectChanges();
+
+        sliderDebugElement = fixture.debugElement.query(By.directive(MdSlider));
+        sliderNativeElement = sliderDebugElement.nativeElement;
+        sliderInstance = sliderDebugElement.injector.get(MdSlider);
+        sliderTrackElement = <HTMLElement>sliderNativeElement.querySelector('.md-slider-track');
+        sliderDimensions = sliderTrackElement.getBoundingClientRect();
+        trackFillElement = <HTMLElement>sliderNativeElement.querySelector('.md-slider-track-fill');
+        thumbElement = <HTMLElement>sliderNativeElement.querySelector('.md-slider-thumb-position');
+      });
+    }));
+
+    it('should set the correct step value on click', () => {
+      expect(sliderInstance.value).toBe(0);
+
+      dispatchClickEvent(sliderTrackElement, 0.13);
+      fixture.detectChanges();
+
+      expect(sliderInstance.value).toBe(25);
+    });
+
+    it('should snap the thumb and fill to a step on click', () => {
+      dispatchClickEvent(sliderNativeElement, 0.66);
+      fixture.detectChanges();
+
+      let trackFillDimensions = trackFillElement.getBoundingClientRect();
+      let thumbDimensions = thumbElement.getBoundingClientRect();
+      let thumbPosition = thumbDimensions.left - trackFillDimensions.left;
+
+      // The closest step is at 75% of the slider.
+      expect(thumbDimensions.left).toBe(sliderDimensions.width * 0.75 + sliderDimensions.left);
+      expect(Math.round(trackFillDimensions.width)).toBe(Math.round(thumbPosition));
+    });
+
+    it('should set the correct step value on drag', () => {
+      dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.07, gestureConfig);
+      fixture.detectChanges();
+
+      expect(sliderInstance.value).toBe(0);
+    });
+
+    it('should snap the thumb and fill to a step on drag', () => {
+      dispatchDragEvent(sliderTrackElement, sliderNativeElement, 0, 0.88, gestureConfig);
+      fixture.detectChanges();
+
+      dispatchDragEndEvent(sliderNativeElement, 0.88, gestureConfig);
+      fixture.detectChanges();
+
+      let trackFillDimensions = trackFillElement.getBoundingClientRect();
+      let thumbDimensions = thumbElement.getBoundingClientRect();
+      let thumbPosition = thumbDimensions.left - trackFillDimensions.left;
+
+      // The closest snap is at the end of the slider.
+      expect(thumbDimensions.left).toBe(sliderDimensions.width + sliderDimensions.left);
+      expect(Math.round(trackFillDimensions.width)).toBe(Math.round(thumbPosition));
+    });
+  });
 });
 
 // The transition has to be removed in order to test the updated positions without setTimeout.
@@ -335,7 +442,13 @@ class DisabledSlider { }
 
 @Component({
   directives: [MD_SLIDER_DIRECTIVES],
-  template: `<md-slider min="5" max="15"></md-slider>`
+  template: `<md-slider min="4" max="6"></md-slider>`,
+  styles: [`
+    .md-slider-track-fill, .md-slider-thumb-position {
+        transition: none !important;
+    }
+  `],
+  encapsulation: ViewEncapsulation.None
 })
 class SliderWithMinAndMax { }
 
@@ -345,8 +458,21 @@ class SliderWithMinAndMax { }
 })
 class SliderWithValue { }
 
+@Component({
+  directives: [MD_SLIDER_DIRECTIVES],
+  template: `<md-slider step="25"></md-slider>`,
+  styles: [`
+    .md-slider-track-fill, .md-slider-thumb-position {
+        transition: none !important;
+    }
+  `],
+  encapsulation: ViewEncapsulation.None
+})
+class SliderWithStep { }
+
 /**
  * Dispatches a click event from an element.
+ * Note: The mouse event truncates the position for the click.
  * @param element The element from which the event will be dispatched.
  * @param percentage The percentage of the slider where the click should occur. Used to find the
  * physical location of the click.