Add support for drawing tick marks on the slider

src/components/slider/slider.html

@@ -5,6 +5,8 @@
     <div class="md-slider-track-container">
       <div class="md-slider-track"></div>
       <div class="md-slider-track md-slider-track-fill"></div>
+      <div class="md-slider-tick-container"></div>
+      <div class="md-slider-last-tick-container"></div>
     </div>
     <div class="md-slider-thumb-container">
       <div class="md-slider-thumb-position">

src/components/slider/slider.scss

@@ -95,6 +95,13 @@ md-slider *::after {
   background-color: md-color($md-accent);
 }
 
+.md-slider-tick-container, .md-slider-last-tick-container {
+  position: absolute;
+  left: 0;
+  right: 0;
+  height: 100%;
+}
+
 .md-slider-thumb-container {
   position: absolute;
   left: 0;

src/components/slider/slider.spec.ts

@@ -25,6 +25,8 @@ describe('MdSlider', () => {
         SliderWithMinAndMax,
         SliderWithValue,
         SliderWithStep,
+        SliderWithAutoTickInterval,
+        SliderWithSetTickInterval
       ],
     });
 
@@ -434,6 +436,86 @@ describe('MdSlider', () => {
       expect(Math.round(trackFillDimensions.width)).toBe(Math.round(thumbPosition));
     });
   });
+
+  describe('slider with auto ticks', () => {
+    let fixture: ComponentFixture<SliderWithAutoTickInterval>;
+    let sliderDebugElement: DebugElement;
+    let sliderNativeElement: HTMLElement;
+    let tickContainer: HTMLElement;
+    let lastTickContainer: HTMLElement;
+
+    beforeEach(async(() => {
+      builder.createAsync(SliderWithAutoTickInterval).then(f => {
+        fixture = f;
+        fixture.detectChanges();
+
+        sliderDebugElement = fixture.debugElement.query(By.directive(MdSlider));
+        sliderNativeElement = sliderDebugElement.nativeElement;
+        tickContainer = <HTMLElement>sliderNativeElement.querySelector('.md-slider-tick-container');
+        lastTickContainer =
+            <HTMLElement>sliderNativeElement.querySelector('.md-slider-last-tick-container');
+      });
+    }));
+
+    it('should set the correct tick separation', () => {
+      // The first tick mark is going to be at value 30 as it is the first step after 30px. The
+      // width of the slider is 112px because the minimum width is 128px with padding of 8px on
+      // both sides. The value 30 will be located at the position 33.6px, and 1px is removed from
+      // the tick mark location in order to center the tick. Therefore, the tick separation should
+      // be 32.6px.
+      // toContain is used rather than toBe because FireFox adds 'transparent' to the beginning
+      // of the background before the repeating linear gradient.
+      expect(tickContainer.style.background).toContain('repeating-linear-gradient(to right, ' +
+          'black, black 2px, transparent 2px, transparent 32.6px)');
+    });
+
+    it('should draw a tick mark on the end of the track', () => {
+      expect(lastTickContainer.style.background).toContain('linear-gradient(to left, black, black' +
+          ' 2px, transparent 2px, transparent)');
+    });
+
+    it('should not draw the second to last tick when it is too close to the last tick', () => {
+      // When the second to last tick is too close (less than half the tick separation) to the last
+      // one, the tick container width is cut by the tick separation, which removes the second to
+      // last tick. Since the width of the slider is 112px and the tick separation is 33.6px, the
+      // tick container width should be 78.4px (112 - 33.6).
+      expect(tickContainer.style.width).toBe('78.4px');
+    });
+  });
+
+  describe('slider with set tick interval', () => {
+    let fixture: ComponentFixture<SliderWithSetTickInterval>;
+    let sliderDebugElement: DebugElement;
+    let sliderNativeElement: HTMLElement;
+    let tickContainer: HTMLElement;
+    let lastTickContainer: HTMLElement;
+
+    beforeEach(async(() => {
+      builder.createAsync(SliderWithSetTickInterval).then(f => {
+        fixture = f;
+        fixture.detectChanges();
+
+        sliderDebugElement = fixture.debugElement.query(By.directive(MdSlider));
+        sliderNativeElement = sliderDebugElement.nativeElement;
+        tickContainer = <HTMLElement>sliderNativeElement.querySelector('.md-slider-tick-container');
+        lastTickContainer =
+            <HTMLElement>sliderNativeElement.querySelector('.md-slider-last-tick-container');
+      });
+    }));
+
+    it('should set the correct tick separation', () => {
+      // The slider width is 112px, the first step is at value 18 (step of 3 * tick interval of 6),
+      // which is at the position 20.16px and 1px is subtracted to center, giving a tick
+      // separation of 19.16px.
+      expect(tickContainer.style.background).toContain('repeating-linear-gradient(to right, ' +
+          'black, black 2px, transparent 2px, transparent 19.16px)');
+    });
+
+    it('should draw a tick mark on the end of the track', () => {
+      expect(lastTickContainer.style.background).toContain('linear-gradient(to left, black, '
+          + 'black 2px, transparent 2px, transparent)');
+    });
+  });
 });
 
 // The transition has to be removed in order to test the updated positions without setTimeout.
@@ -480,6 +562,16 @@ class SliderWithValue { }
 })
 class SliderWithStep { }
 
+@Component({
+  template: `<md-slider step="5" tick-interval="auto"></md-slider>`
+})
+class SliderWithAutoTickInterval { }
+
+@Component({
+  template: `<md-slider step="3" tick-interval="6"></md-slider>`
+})
+class SliderWithSetTickInterval { }
+
 /**
  * Dispatches a click event from an element.
  * Note: The mouse event truncates the position for the click.

src/components/slider/slider.ts

@@ -12,6 +12,12 @@ import {BooleanFieldValue} from '@angular2-material/core/annotations/field-value
 import {applyCssTransform} from '@angular2-material/core/style/apply-transform';
 import {MdGestureConfig} from '@angular2-material/core/core';
 
+/**
+ * Visually, a 30px separation between tick marks looks best. This is very subjective but it is
+ * the default separation we chose.
+ */
+const MIN_AUTO_TICK_SEPARATION = 30;
+
 @Component({
   moduleId: module.id,
   selector: 'md-slider',
@@ -53,6 +59,12 @@ export class MdSlider implements AfterContentInit {
   /** The values at which the thumb will snap. */
   @Input() step: number = 1;
 
+  /**
+   * How often to show ticks. Relative to the step so that a tick always appears on a step.
+   * Ex: Tick interval of 4 with a step of 3 will draw a tick every 4 steps (every 12 values).
+   */
+  @Input('tick-interval') private _tickInterval: 'auto' | number;
+
   /**
    * Whether or not the thumb is sliding.
    * Used to determine if there should be a transition for the thumb and fill track.
@@ -122,6 +134,7 @@ export class MdSlider implements AfterContentInit {
   ngAfterContentInit() {
     this._sliderDimensions = this._renderer.getSliderDimensions();
     this.snapToValue();
+    this._updateTickSeparation();
   }
 
   /** TODO: internal */
@@ -186,7 +199,7 @@ export class MdSlider implements AfterContentInit {
    * This is also used to move the thumb to a snapped value once sliding is done.
    */
   updatePercentFromValue() {
-    this._percent = (this.value - this.min) / (this.max - this.min);
+    this._percent = this.calculatePercentage(this.value);
   }
 
   /**
@@ -198,7 +211,7 @@ export class MdSlider implements AfterContentInit {
 
     // The exact value is calculated from the event and used to find the closest snap value.
     this._percent = this.clamp((pos - offset) / size);
-    let exactValue = this.min + (this._percent * (this.max - this.min));
+    let exactValue = this.calculateValue(this._percent);
 
     // This calculation finds the closest step by finding the closest whole number divisible by the
     // step relative to the min.
@@ -217,6 +230,80 @@ export class MdSlider implements AfterContentInit {
     this._renderer.updateThumbAndFillPosition(this._percent, this._sliderDimensions.width);
   }
 
+  /**
+   * Calculates the separation in pixels of tick marks. If there is no tick interval or the interval
+   * is set to something other than a number or 'auto', nothing happens.
+   */
+  private _updateTickSeparation() {
+    if (this._tickInterval == 'auto') {
+      this._updateAutoTickSeparation();
+    } else if (Number(this._tickInterval)) {
+      this._updateTickSeparationFromInterval();
+    }
+  }
+
+  /**
+   * Calculates the optimal separation in pixels of tick marks based on the minimum auto tick
+   * separation constant.
+   */
+  private _updateAutoTickSeparation() {
+    // We're looking for the multiple of step for which the separation between is greater than the
+    // minimum tick separation.
+    let sliderWidth = this._sliderDimensions.width;
+
+    // This is the total "width" of the slider in terms of values.
+    let valueWidth = this.max - this.min;
+
+    // Calculate how many values exist within 1px on the slider.
+    let valuePerPixel = valueWidth / sliderWidth;
+
+    // Calculate how many values exist in the minimum tick separation (px).
+    let valuePerSeparation = valuePerPixel  * MIN_AUTO_TICK_SEPARATION;
+
+    // Calculate how many steps exist in this separation. This will be the lowest value you can
+    // multiply step by to get a separation that is greater than or equal to the minimum tick
+    // separation.
+    let stepsPerSeparation = Math.ceil(valuePerSeparation / this.step);
+
+    // Get the percentage of the slider for which this tick would be located so we can then draw
+    // it on the slider.
+    let tickPercentage = this.calculatePercentage((this.step * stepsPerSeparation) + this.min);
+
+    // The pixel value of the tick is the percentage * the width of the slider. Use this to draw
+    // the ticks on the slider.
+    this._renderer.drawTicks(sliderWidth * tickPercentage);
+  }
+
+  /**
+   * Calculates the separation of tick marks by finding the pixel value of the tickInterval.
+   */
+  private _updateTickSeparationFromInterval() {
+    // Force tickInterval to be a number so it can be used in calculations.
+    let interval: number = <number> this._tickInterval;
+    // Calculate the first value a tick will be located at by getting the step at which the interval
+    // lands and adding that to the min.
+    let tickValue = (this.step * interval) + this.min;
+
+    // The percentage of the step on the slider is needed in order to calculate the pixel offset
+    // from the beginning of the slider. This offset is the tick separation.
+    let tickPercentage = this.calculatePercentage(tickValue);
+    this._renderer.drawTicks(this._sliderDimensions.width * tickPercentage);
+  }
+
+  /**
+   * Calculates the percentage of the slider that a value is.
+   */
+  calculatePercentage(value: number) {
+    return (value - this.min) / (this.max - this.min);
+  }
+
+  /**
+   * Calculates the value a percentage of the slider corresponds to.
+   */
+  calculateValue(percentage: number) {
+    return this.min + (percentage * (this.max - this.min));
+  }
+
   /**
    * Return a number between two numbers.
    */
@@ -267,6 +354,32 @@ export class SliderRenderer {
   addFocus() {
     this._sliderElement.focus();
   }
+
+  /**
+   * Draws ticks onto the tick container.
+   */
+  drawTicks(tickSeparation: number) {
+    let tickContainer = <HTMLElement>this._sliderElement.querySelector('.md-slider-tick-container');
+    let tickContainerWidth = tickContainer.getBoundingClientRect().width;
+    // An extra element for the last tick is needed because the linear gradient cannot be told to
+    // always draw a tick at the end of the gradient. To get around this, there is a second
+    // container for ticks that has a single tick mark on the very right edge.
+    let lastTickContainer =
+        <HTMLElement>this._sliderElement.querySelector('.md-slider-last-tick-container');
+    // Subtract 1 from the tick separation to center the tick.
+    // TODO: Evaluate the rendering performance of using repeating background gradients.
+    tickContainer.style.background = `repeating-linear-gradient(to right, black, black 2px, ` +
+        `transparent 2px, transparent ${tickSeparation - 1}px)`;
+    // Add a tick to the very end by starting on the right side and adding a 2px black line.
+    lastTickContainer.style.background = `linear-gradient(to left, black, black 2px, transparent ` +
+        `2px, transparent)`;
+
+    // If the second to last tick is too close (a separation of less than half the normal
+    // separation), don't show it by decreasing the width of the tick container element.
+    if (tickContainerWidth % tickSeparation < (tickSeparation / 2)) {
+      tickContainer.style.width = tickContainerWidth - tickSeparation + 'px';
+    }
+  }
 }
 
 export const MD_SLIDER_DIRECTIVES = [MdSlider];

src/demo-app/slider/slider-demo.html

@@ -26,3 +26,7 @@ <h1>Slider with step defined</h1>
   <md-slider min="1" max="100" step="20" #slider5></md-slider>
   {{slider5.value}}
 </section>
+
+<h1>Slider with set tick interval</h1>
+<md-slider tick-interval="auto"></md-slider>
+<md-slider tick-interval="9"></md-slider>