From 49d0c981804bbe0b109549142a0ba68db960fc2c Mon Sep 17 00:00:00 2001
From: Kara <kara@users.noreply.github.com>
Date: Fri, 2 Dec 2016 13:34:33 -0800
Subject: [PATCH] feat(select): align selected option over trigger (#2026)

Closes #1669
---
 src/demo-app/select/select-demo.html |   2 +
 src/demo-app/select/select-demo.ts   |  10 +-
 src/lib/select/select-animations.ts  |  19 +-
 src/lib/select/select.html           |   4 +-
 src/lib/select/select.scss           |   4 +-
 src/lib/select/select.spec.ts        | 316 ++++++++++++++++++++++-----
 src/lib/select/select.ts             | 259 ++++++++++++++++++++--
 7 files changed, 522 insertions(+), 92 deletions(-)

diff --git a/src/demo-app/select/select-demo.html b/src/demo-app/select/select-demo.html
index 467c15ce3658..9e5c8dc3e122 100644
--- a/src/demo-app/select/select-demo.html
+++ b/src/demo-app/select/select-demo.html
@@ -1,3 +1,4 @@
+<div style="height: 1000px">This div is for testing scrolled selects.</div>
 <div class="demo-select">
   <md-card>
     <md-select placeholder="Food i would like to eat" [formControl]="foodControl">
@@ -28,3 +29,4 @@
   </md-card>
 
 </div>
+<div style="height: 500px">This div is for testing scrolled selects.</div>
diff --git a/src/demo-app/select/select-demo.ts b/src/demo-app/select/select-demo.ts
index 7bd1c6cda590..29c4f5eeb863 100644
--- a/src/demo-app/select/select-demo.ts
+++ b/src/demo-app/select/select-demo.ts
@@ -21,8 +21,14 @@ export class SelectDemo {
 
   drinks = [
     {value: 'coke-0', viewValue: 'Coke'},
-    {value: 'sprite-1', viewValue: 'Sprite', disabled: true},
-    {value: 'water-2', viewValue: 'Water'}
+    {value: 'sprite-1', viewValue: 'Sprite'},
+    {value: 'water-2', viewValue: 'Water'},
+    {value: 'pepper-3', viewValue: 'Dr. Pepper'},
+    {value: 'coffee-4', viewValue: 'Coffee'},
+    {value: 'tea-5', viewValue: 'Tea'},
+    {value: 'juice-6', viewValue: 'Orange juice'},
+    {value: 'wine-7', viewValue: 'Wine'},
+    {value: 'milk-8', viewValue: 'Milk'},
   ];
 
   toggleDisabled() {
diff --git a/src/lib/select/select-animations.ts b/src/lib/select/select-animations.ts
index 238341138c39..677633853868 100644
--- a/src/lib/select/select-animations.ts
+++ b/src/lib/select/select-animations.ts
@@ -42,25 +42,10 @@ export const transformPlaceholder: AnimationEntryMetadata = trigger('transformPl
  * When the panel is removed from the DOM, it simply fades out linearly.
  */
 export const transformPanel: AnimationEntryMetadata = trigger('transformPanel', [
-  state('top-ltr', style({
+  state('showing', style({
     opacity: 1,
     width: 'calc(100% + 32px)',
-    transform: `translate3d(-16px, -9px, 0) scaleY(1)`
-  })),
-  state('top-rtl', style({
-    opacity: 1,
-    width: 'calc(100% + 32px)',
-    transform: `translate3d(16px, -9px, 0) scaleY(1)`
-  })),
-  state('bottom-ltr', style({
-    opacity: 1,
-    width: 'calc(100% + 32px)',
-    transform: `translate3d(-16px, 8px, 0) scaleY(1)`
-  })),
-  state('bottom-rtl', style({
-    opacity: 1,
-    width: 'calc(100% + 32px)',
-    transform: `translate3d(16px, 8px, 0) scaleY(1)`
+    transform: `translate3d(0,0,0) scaleY(1)`
   })),
   transition('void => *', [
     style({
diff --git a/src/lib/select/select.html b/src/lib/select/select.html
index f95dc6b1c6e8..0de3f7ae2162 100644
--- a/src/lib/select/select.html
+++ b/src/lib/select/select.html
@@ -6,8 +6,8 @@
 
 <template connected-overlay [origin]="origin"  [open]="panelOpen" hasBackdrop (backdropClick)="close()"
   backdropClass="md-overlay-transparent-backdrop" [positions]="_positions" [width]="_getWidth()"
-  (positionChange)="_updateTransformOrigin($event)">
-  <div class="md-select-panel" [@transformPanel]="_getPanelState()" (@transformPanel.done)="_onPanelDone()"
+  [offsetY]="_offsetY" [offsetX]="_offsetX" (attach)="_setScrollTop()">
+  <div class="md-select-panel" [@transformPanel]="'showing'" (@transformPanel.done)="_onPanelDone()"
     (keydown)="_keyManager.onKeydown($event)" [style.transformOrigin]="_transformOrigin">
     <div class="md-select-content" [@fadeInContent]="'showing'">
       <ng-content></ng-content>
diff --git a/src/lib/select/select.scss b/src/lib/select/select.scss
index 60f1a1e49e68..849294dfb2d0 100644
--- a/src/lib/select/select.scss
+++ b/src/lib/select/select.scss
@@ -5,6 +5,7 @@ $md-select-trigger-height: 30px !default;
 $md-select-trigger-min-width: 112px !default;
 $md-select-arrow-size: 5px !default;
 $md-select-arrow-margin: 4px !default;
+$md-select-panel-max-height: 256px !default;
 
 md-select {
   display: inline-block;
@@ -19,6 +20,7 @@ md-select {
   min-width: $md-select-trigger-min-width;
   cursor: pointer;
   position: relative;
+  box-sizing: border-box;
 
   [aria-disabled='true'] & {
     @include md-control-disabled-underline();
@@ -78,7 +80,7 @@ md-select {
   @include md-menu-base();
   padding-top: 0;
   padding-bottom: 0;
-  transform-origin: top;
+  max-height: $md-select-panel-max-height;
 }
 
 md-option {
diff --git a/src/lib/select/select.spec.ts b/src/lib/select/select.spec.ts
index 1c0dddabc878..023d4d3e8c66 100644
--- a/src/lib/select/select.spec.ts
+++ b/src/lib/select/select.spec.ts
@@ -208,16 +208,16 @@ describe('MdSelect', () => {
     }));
 
     it('should select an option that was added after initialization', () => {
-      fixture.componentInstance.foods.push({viewValue: 'Pasta', value: 'pasta-3'});
+      fixture.componentInstance.foods.push({viewValue: 'Potatoes', value: 'potatoes-8'});
       trigger.click();
       fixture.detectChanges();
 
       const options =
         overlayContainerElement.querySelectorAll('md-option') as NodeListOf<HTMLElement>;
-      options[3].click();
+      options[8].click();
       fixture.detectChanges();
 
-      expect(trigger.textContent).toContain('Pasta');
+      expect(trigger.textContent).toContain('Potatoes');
       expect(fixture.componentInstance.select.selected)
         .toBe(fixture.componentInstance.options.last);
     });
@@ -490,79 +490,280 @@ describe('MdSelect', () => {
         expect(fixture.componentInstance.select._getPlaceholderState()).toEqual('floating-rtl');
       });
 
-      it('should use the ltr panel state when the dir is ltr', () => {
-        dir.value = 'ltr';
+  });
+
+  describe('positioning', () => {
+    let fixture: ComponentFixture<BasicSelect>;
+    let trigger: HTMLElement;
+    let select: HTMLElement;
+
+    beforeEach(() => {
+      fixture = TestBed.createComponent(BasicSelect);
+      fixture.detectChanges();
+      trigger = fixture.debugElement.query(By.css('.md-select-trigger')).nativeElement;
+      select = fixture.debugElement.query(By.css('md-select')).nativeElement;
+    });
+
+    /**
+     * Asserts that the given option is aligned with the trigger.
+     * @param index The index of the option.
+     */
+    function checkTriggerAlignedWithOption(index: number): void {
+      const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+      const triggerTop = trigger.getBoundingClientRect().top;
+      const overlayTop = overlayPane.getBoundingClientRect().top;
+      const options = overlayPane.querySelectorAll('md-option');
+      const optionTop = options[index].getBoundingClientRect().top;
+
+      // The option text should align with the trigger text. Because each option is 18px
+      // larger in height than the trigger, the option needs to be adjusted up 9 pixels.
+      expect(optionTop.toFixed(2))
+          .toEqual((triggerTop - 9).toFixed(2), `Expected trigger to align with option ${index}.`);
+
+      // For the animation to start at the option's center, its origin must be the distance
+      // from the top of the overlay to the option top + half the option height (48/2 = 24).
+      const expectedOrigin = optionTop - overlayTop + 24;
+      expect(fixture.componentInstance.select._transformOrigin)
+          .toContain(`${expectedOrigin}px`,
+              `Expected panel animation to originate in the center of option ${index}.`);
+    }
+
+    describe('ample space to open', () => {
 
+      beforeEach(() => {
+        // these styles are necessary because we are first testing the overlay's position
+        // if there is room for it to open to its full extent in either direction.
+        select.style.marginTop = '300px';
+        select.style.marginLeft = '20px';
+        select.style.marginRight = '20px';
+      });
+
+      it('should align the first option with the trigger text if no option is selected', () => {
         trigger.click();
         fixture.detectChanges();
-        expect(fixture.componentInstance.select._getPanelState()).toEqual('top-ltr');
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // The panel should be scrolled to 0 because centering the option is not possible.
+        expect(scrollContainer.scrollTop).toEqual(0, `Expected panel not to be scrolled.`);
+
+        checkTriggerAlignedWithOption(0);
       });
 
-      it('should use the rtl panel state when the dir is rtl', () => {
-        dir.value = 'rtl';
+      it('should align a selected option too high to be centered with the trigger text', () => {
+        // Select the second option, because it can't be scrolled any further downward
+        fixture.componentInstance.control.setValue('pizza-1');
+        fixture.detectChanges();
 
         trigger.click();
         fixture.detectChanges();
-        expect(fixture.componentInstance.select._getPanelState()).toEqual('top-rtl');
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // The panel should be scrolled to 0 because centering the option is not possible.
+        expect(scrollContainer.scrollTop).toEqual(0, `Expected panel not to be scrolled.`);
+
+        checkTriggerAlignedWithOption(1);
       });
 
-  });
+      it('should align a selected option in the middle with the trigger text', () => {
+        // Select the fifth option, which has enough space to scroll to the center
+        fixture.componentInstance.control.setValue('chips-4');
+        fixture.detectChanges();
 
-  describe('positioning', () => {
-    let fixture: ComponentFixture<BasicSelect>;
-    let trigger: HTMLElement;
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // The selected option should be scrolled to the center of the panel.
+        // This will be its original offset from the scrollTop - half the panel height + half the
+        // option height. 4 (index) * 48 (option height) = 192px offset from scrollTop
+        // 192 - 256/2 + 48/2 = 88px
+        expect(scrollContainer.scrollTop)
+            .toEqual(88, `Expected overlay panel to be scrolled to center the selected option.`);
+
+        checkTriggerAlignedWithOption(4);
+      });
+
+      it('should align a selected option at the scroll max with the trigger text', () => {
+        // Select the last option in the list
+        fixture.componentInstance.control.setValue('sushi-7');
+        fixture.detectChanges();
+
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // The selected option should be scrolled to the max scroll position.
+        // This will be the height of the scrollContainer - the panel height.
+        // 8 options * 48px = 384 scrollContainer height, 384 - 256 = 128px max scroll
+        expect(scrollContainer.scrollTop)
+            .toEqual(128, `Expected overlay panel to be scrolled to its maximum position.`);
+
+        checkTriggerAlignedWithOption(7);
+      });
 
-    beforeEach(() => {
-      fixture = TestBed.createComponent(BasicSelect);
-      fixture.detectChanges();
-      trigger = fixture.debugElement.query(By.css('.md-select-trigger')).nativeElement;
     });
 
-    it('should open below the trigger if the panel will fit', () => {
-      trigger.click();
-      fixture.detectChanges();
+    describe('limited space to open vertically', () => {
 
-      const overlayPane = overlayContainerElement.children[0] as HTMLElement;
-      const overlayRect = overlayPane.getBoundingClientRect();
-      const triggerRect = trigger.getBoundingClientRect();
+      beforeEach(() => {
+        select.style.marginLeft = '20px';
+        select.style.marginRight = '20px';
+      });
 
-      // when the select panel opens below the trigger, the tops of the trigger and the overlay
-      // should be aligned.
-      expect(overlayRect.top.toFixed(2))
-          .toEqual(triggerRect.top.toFixed(2), `Expected panel to open below by default.`);
+      it('should adjust position of centered option if there is little space above', () => {
+        // Push the select to a position with not quite enough space on the top to open
+        // with the option completely centered (needs 113px at least: 256/2 - 48/2 + 9)
+        select.style.marginTop = '85px';
+
+        // Select an option in the middle of the list
+        fixture.componentInstance.control.setValue('chips-4');
+        fixture.detectChanges();
+
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // Scroll should adjust by the difference between the top space available (85px + 8px
+        // viewport padding = 77px) and the height of the panel above the option (113px).
+        // 113px - 77px = 36px difference + original scrollTop 88px = 124px
+        expect(scrollContainer.scrollTop)
+            .toEqual(124, `Expected panel to adjust scroll position to fit in viewport.`);
+
+        checkTriggerAlignedWithOption(4);
+      });
+
+      it('should adjust position of centered option if there is little space below', () => {
+        // Push the select to a position with not quite enough space on the bottom to open
+        // with the option completely centered (needs 113px at least: 256/2 - 48/2 + 9)
+        select.style.marginTop = '600px';
+
+        // Select an option in the middle of the list
+        fixture.componentInstance.control.setValue('chips-4');
+        fixture.detectChanges();
+
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // Scroll should adjust by the difference between the bottom space available
+        // (686px - 600px margin - 30px trigger height = 56px - 8px padding = 48px)
+        // and the height of the panel below the option (113px).
+        // 113px - 48px = 75px difference. Original scrollTop 88px - 75px = 23px
+        expect(scrollContainer.scrollTop)
+            .toEqual(23, `Expected panel to adjust scroll position to fit in viewport.`);
+
+        checkTriggerAlignedWithOption(4);
+      });
+
+      it('should fall back to "above" positioning if scroll adjustment will not help', () => {
+        // Push the select to a position with not enough space on the bottom to open
+        select.style.marginTop = '600px';
+        fixture.detectChanges();
+
+        // Select an option that cannot be scrolled any farther upward
+        fixture.componentInstance.control.setValue('coke-0');
+        fixture.detectChanges();
+
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const triggerBottom = trigger.getBoundingClientRect().bottom;
+        const overlayBottom = overlayPane.getBoundingClientRect().bottom;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // Expect no scroll to be attempted
+        expect(scrollContainer.scrollTop).toEqual(0, `Expected panel not to be scrolled.`);
+
+        expect(overlayBottom.toFixed(2))
+            .toEqual(triggerBottom.toFixed(2),
+                `Expected trigger bottom to align with overlay bottom.`);
+
+        expect(fixture.componentInstance.select._transformOrigin)
+            .toContain(`bottom`, `Expected panel animation to originate at the bottom.`);
+      });
+
+      it('should fall back to "below" positioning if scroll adjustment will not help', () => {
+        // Push the select to a position with not enough space on the top to open
+        select.style.marginTop = '85px';
+
+        // Select an option that cannot be scrolled any farther downward
+        fixture.componentInstance.control.setValue('sushi-7');
+        fixture.detectChanges();
+
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const triggerTop = trigger.getBoundingClientRect().top;
+        const overlayTop = overlayPane.getBoundingClientRect().top;
+        const scrollContainer = overlayPane.querySelector('.md-select-panel');
+
+        // Expect scroll to remain at the max scroll position
+        expect(scrollContainer.scrollTop).toEqual(128, `Expected panel to be at max scroll.`);
+
+        expect(overlayTop.toFixed(2))
+            .toEqual(triggerTop.toFixed(2), `Expected trigger top to align with overlay top.`);
+
+        expect(fixture.componentInstance.select._transformOrigin)
+            .toContain(`top`, `Expected panel animation to originate at the top.`);
+      });
 
-      // animation should match the position
-      expect(fixture.componentInstance.select._getPanelState())
-          .toEqual('top-ltr', `Expected panel animation values to match the position.`);
-      expect(fixture.componentInstance.select._transformOrigin)
-          .toBe('top', `Expected panel animation to originate at the top.`);
     });
 
-    it('should open above the trigger if there is not space below for the panel', () => {
-      // Push trigger to the bottom part of viewport, so it doesn't have space to open
-      // in its default position below the trigger.
-      trigger.style.position = 'relative';
-      trigger.style.top = '650px';
+    describe('x-axis positioning', () => {
 
-      trigger.click();
-      fixture.detectChanges();
+      beforeEach(() => {
+        select.style.marginLeft = '20px';
+        select.style.marginRight = '20px';
+      });
+
+      it('should align the trigger and the selected option on the x-axis in ltr', () => {
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const triggerLeft = trigger.getBoundingClientRect().left;
+        const firstOptionLeft =
+            overlayPane.querySelector('md-option').getBoundingClientRect().left;
+
+        // Each option is 32px wider than the trigger, so it must be adjusted 16px
+        // to ensure the text overlaps correctly.
+        expect(firstOptionLeft.toFixed(2))
+            .toEqual((triggerLeft - 16).toFixed(2),
+                `Expected trigger to align with the selected option on the x-axis in LTR.`);
+      });
+
+      it('should align the trigger and the selected option on the x-axis in rtl', () => {
+        dir.value = 'rtl';
+
+        trigger.click();
+        fixture.detectChanges();
+
+        const overlayPane = overlayContainerElement.children[0] as HTMLElement;
+        const triggerRight = trigger.getBoundingClientRect().right;
+        const firstOptionRight =
+            overlayPane.querySelector('md-option').getBoundingClientRect().right;
+
+        // Each option is 32px wider than the trigger, so it must be adjusted 16px
+        // to ensure the text overlaps correctly.
+        expect(firstOptionRight.toFixed(2))
+            .toEqual((triggerRight + 16).toFixed(2),
+                `Expected trigger to align with the selected option on the x-axis in RTL.`);
+      });
 
-      const overlayPane = overlayContainerElement.children[0] as HTMLElement;
-      const overlayRect = overlayPane.getBoundingClientRect();
-      const triggerRect = trigger.getBoundingClientRect();
-
-      // In "above" position, the bottom edges of the overlay and the origin are aligned.
-      // To find the overlay top, subtract the panel height from the origin's bottom edge.
-      const expectedTop = triggerRect.bottom - overlayRect.height;
-      expect(overlayRect.top.toFixed(2))
-          .toEqual(expectedTop.toFixed(2),
-              `Expected panel to open above the trigger if below wouldn't fit.`);
-
-      // animation should match the position
-      expect(fixture.componentInstance.select._getPanelState())
-          .toEqual('bottom-ltr', `Expected panel animation values to match the position.`);
-      expect(fixture.componentInstance.select._transformOrigin)
-          .toBe('bottom', `Expected panel animation to originate at the bottom.`);
     });
 
   });
@@ -784,6 +985,11 @@ class BasicSelect {
     { value: 'steak-0', viewValue: 'Steak' },
     { value: 'pizza-1', viewValue: 'Pizza' },
     { value: 'tacos-2', viewValue: 'Tacos', disabled: true },
+    { value: 'sandwich-3', viewValue: 'Sandwich' },
+    { value: 'chips-4', viewValue: 'Chips' },
+    { value: 'eggs-5', viewValue: 'Eggs' },
+    { value: 'pasta-6', viewValue: 'Pasta' },
+    { value: 'sushi-7', viewValue: 'Sushi' },
   ];
   control = new FormControl();
   isRequired: boolean;
diff --git a/src/lib/select/select.ts b/src/lib/select/select.ts
index 6fbc9384f989..974bac7ad6f6 100644
--- a/src/lib/select/select.ts
+++ b/src/lib/select/select.ts
@@ -12,7 +12,7 @@ import {
   QueryList,
   Renderer,
   ViewEncapsulation,
-  ViewChild
+  ViewChild,
 } from '@angular/core';
 import {MdOption} from './option';
 import {ENTER, SPACE} from '../core/keyboard/keycodes';
@@ -22,7 +22,48 @@ import {Subscription} from 'rxjs/Subscription';
 import {transformPlaceholder, transformPanel, fadeInContent} from './select-animations';
 import {ControlValueAccessor, NgControl} from '@angular/forms';
 import {coerceBooleanProperty} from '../core/coersion/boolean-property';
-import {ConnectedOverlayPositionChange} from '../core/overlay/position/connected-position';
+import {ConnectedOverlayDirective} from '../core/overlay/overlay-directives';
+import {ViewportRuler} from '../core/overlay/position/viewport-ruler';
+
+/**
+ * The following style constants are necessary to save here in order
+ * to properly calculate the alignment of the selected option over
+ * the trigger element.
+ */
+
+/** The fixed height of every option element. */
+export const SELECT_OPTION_HEIGHT = 48;
+
+/** The max height of the select's overlay panel */
+export const SELECT_PANEL_MAX_HEIGHT = 256;
+
+/** The max number of options visible at once in the select panel. */
+export const SELECT_MAX_OPTIONS_DISPLAYED = 5;
+
+/** The fixed height of the select's trigger element. */
+export const SELECT_TRIGGER_HEIGHT = 30;
+
+/**
+ * Must adjust for the difference in height between the option and the trigger,
+ * so the text will align on the y axis.
+ * (SELECT_OPTION_HEIGHT (48) - SELECT_TRIGGER_HEIGHT (30)) / 2 = 9
+ */
+export const SELECT_OPTION_HEIGHT_ADJUSTMENT = 9;
+
+/** The panel's padding on the x-axis */
+export const SELECT_PANEL_PADDING_X = 16;
+
+/**
+ * The panel's padding on the y-axis. This padding indicates there are more
+ * options available if you scroll.
+ */
+export const SELECT_PANEL_PADDING_Y = 16;
+
+/**
+ * The select panel will only "fit" inside the viewport if it is positioned at
+ * this value or more away from the viewport boundary.
+ */
+export const SELECT_PANEL_VIEWPORT_PADDING = 8;
 
 @Component({
   moduleId: module.id,
@@ -71,11 +112,14 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   /** Whether the select is disabled.  */
   private _disabled: boolean = false;
 
+  /** The scroll position of the overlay panel, calculated to center the selected option. */
+  private _scrollTop = 0;
+
   /** Manages keyboard events for options in the panel. */
   _keyManager: ListKeyManager;
 
   /** View -> model callback called when value changes */
-  _onChange: (value: any) => void;
+  _onChange = (value: any) => {};
 
   /** View -> model callback called when select has been touched */
   _onTouched = () => {};
@@ -86,6 +130,20 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   /** The value of the select panel's transform-origin property. */
   _transformOrigin: string = 'top';
 
+  /**
+   * The x-offset of the overlay panel in relation to the trigger's top start corner.
+   * This must be adjusted to align the selected option text over the trigger text when
+   * the panel opens. Will change based on LTR or RTL text direction.
+   */
+  _offsetX = 0;
+
+  /**
+   * The y-offset of the overlay panel in relation to the trigger's top start corner.
+   * This must be adjusted to align the selected option text over the trigger text.
+   * when the panel opens. Will change based on the y-position of the selected option.
+   */
+  _offsetY = 0;
+
   /**
    * This position config ensures that the top "start" corner of the overlay
    * is aligned with with the top "start" of the origin by default (overlapping
@@ -108,6 +166,7 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   ];
 
   @ViewChild('trigger') trigger: ElementRef;
+  @ViewChild(ConnectedOverlayDirective) overlayDir: ConnectedOverlayDirective;
   @ContentChildren(MdOption) options: QueryList<MdOption>;
 
   @Input() placeholder: string;
@@ -134,8 +193,8 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   @Output() onClose = new EventEmitter();
 
   constructor(private _element: ElementRef, private _renderer: Renderer,
-              @Optional() private _dir: Dir, @Optional() public _control: NgControl,
-              private _ngZone: NgZone) {
+              private _ngZone: NgZone, private _viewportRuler: ViewportRuler,
+              @Optional() private _dir: Dir, @Optional() public _control: NgControl) {
     if (this._control) {
       this._control.valueAccessor = this;
     }
@@ -163,6 +222,7 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     if (this.disabled) {
       return;
     }
+    this._calculateOverlayPosition();
     this._panelOpen = true;
   }
 
@@ -237,7 +297,7 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
    * the overlay width to the trigger width.
    */
   _getWidth(): number {
-    return this.trigger.nativeElement.getBoundingClientRect().width;
+    return this._getTriggerRect().width;
   }
 
   /** The animation state of the placeholder. */
@@ -249,11 +309,6 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     }
   }
 
-  /** The animation state of the overlay panel. */
-  _getPanelState(): string {
-    return this._isRtl() ? `${this._transformOrigin}-rtl` : `${this._transformOrigin}-ltr`;
-  }
-
   /** Ensures the panel opens if activated by the keyboard. */
   _handleKeydown(event: KeyboardEvent): void {
     if (event.keyCode === ENTER || event.keyCode === SPACE) {
@@ -289,12 +344,20 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     return this.disabled ? '-1' : '0';
   }
 
+
   /**
-   * Sets the transform-origin property of the panel to ensure that it
-   * animates in the correct direction based on its positioning.
+   * Sets the scroll position of the scroll container. This must be called after
+   * the overlay pane is attached or the scroll container element will not yet be
+   * present in the DOM.
    */
-  _updateTransformOrigin(pos: ConnectedOverlayPositionChange): void {
-    this._transformOrigin = pos.connectionPair.originY;
+  _setScrollTop(): void {
+    const scrollContainer =
+        this.overlayDir.overlayRef.overlayElement.querySelector('.md-select-panel');
+    scrollContainer.scrollTop = this._scrollTop;
+  }
+
+  private _getTriggerRect(): ClientRect {
+    return this.trigger.nativeElement.getBoundingClientRect();
   }
 
   /** Sets up a key manager to listen to keyboard events on the overlay panel. */
@@ -375,4 +438,170 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     }, undefined);
   }
 
+  /** Calculates the scroll position and x- and y-offsets of the overlay panel. */
+  private _calculateOverlayPosition(): void {
+    this._offsetX = this._isRtl() ? SELECT_PANEL_PADDING_X : -SELECT_PANEL_PADDING_X;
+
+    const panelHeight =
+        Math.min(this.options.length * SELECT_OPTION_HEIGHT, SELECT_PANEL_MAX_HEIGHT);
+    const scrollContainerHeight = this.options.length * SELECT_OPTION_HEIGHT;
+
+    // The farthest the panel can be scrolled before it hits the bottom
+    const maxScroll = scrollContainerHeight - panelHeight;
+
+    if (this.selected) {
+      const selectedIndex = this._getOptionIndex(this.selected);
+      // We must maintain a scroll buffer so the selected option will be scrolled to the
+      // center of the overlay panel rather than the top.
+      const scrollBuffer = panelHeight / 2;
+      this._scrollTop = this._calculateOverlayScroll(selectedIndex, scrollBuffer, maxScroll);
+      this._offsetY = this._calculateOverlayOffset(selectedIndex, scrollBuffer, maxScroll);
+    } else {
+      // If no option is selected, the panel centers on the first option. In this case,
+      // we must only adjust for the height difference between the option element
+      // and the trigger element, then multiply it by -1 to ensure the panel moves
+      // in the correct direction up the page.
+      this._offsetY = (SELECT_OPTION_HEIGHT - SELECT_TRIGGER_HEIGHT) / 2 * -1;
+    }
+
+    this._checkOverlayWithinViewport(maxScroll);
+  }
+
+  /**
+   * Calculates the scroll position of the select's overlay panel.
+   *
+   * Attempts to center the selected option in the panel. If the option is
+   * too high or too low in the panel to be scrolled to the center, it clamps the
+   * scroll position to the min or max scroll positions respectively.
+   */
+  _calculateOverlayScroll(selectedIndex: number, scrollBuffer: number,
+                          maxScroll: number): number {
+    const optionOffsetFromScrollTop = SELECT_OPTION_HEIGHT * selectedIndex;
+    const halfOptionHeight = SELECT_OPTION_HEIGHT / 2;
+
+    // Starts at the optionOffsetFromScrollTop, which scrolls the option to the top of the
+    // scroll container, then subtracts the scroll buffer to scroll the option down to
+    // the center of the overlay panel. Half the option height must be re-added to the
+    // scrollTop so the option is centered based on its middle, not its top edge.
+    const optimalScrollPosition = optionOffsetFromScrollTop - scrollBuffer + halfOptionHeight;
+    return clampValue(0, optimalScrollPosition, maxScroll);
+  }
+
+  /**
+   * Calculates the y-offset of the select's overlay panel in relation to the
+   * top start corner of the trigger. It has to be adjusted in order for the
+   * selected option to be aligned over the trigger when the panel opens.
+   */
+  private _calculateOverlayOffset(selectedIndex: number, scrollBuffer: number,
+                                  maxScroll: number): number {
+    let optionOffsetFromPanelTop: number;
+
+    if (this._scrollTop === 0) {
+      optionOffsetFromPanelTop = selectedIndex * SELECT_OPTION_HEIGHT;
+    } else if (this._scrollTop === maxScroll) {
+      const firstDisplayedIndex = this.options.length - SELECT_MAX_OPTIONS_DISPLAYED;
+      const selectedDisplayIndex = selectedIndex - firstDisplayedIndex;
+
+      // Because the panel height is longer than the height of the options alone,
+      // there is always extra padding at the top or bottom of the panel. When
+      // scrolled to the very bottom, this padding is at the top of the panel and
+      // must be added to the offset.
+      optionOffsetFromPanelTop =
+          selectedDisplayIndex * SELECT_OPTION_HEIGHT + SELECT_PANEL_PADDING_Y;
+    } else {
+      // If the option was scrolled to the middle of the panel using a scroll buffer,
+      // its offset will be the scroll buffer minus the half height that was added to
+      // center it.
+      optionOffsetFromPanelTop = scrollBuffer - SELECT_OPTION_HEIGHT / 2;
+    }
+
+    // The final offset is the option's offset from the top, adjusted for the height
+    // difference, multiplied by -1 to ensure that the overlay moves in the correct
+    // direction up the page.
+    return optionOffsetFromPanelTop * -1 - SELECT_OPTION_HEIGHT_ADJUSTMENT;
+  }
+
+  /**
+   * Checks that the attempted overlay position will fit within the viewport.
+   * If it will not fit, tries to adjust the scroll position and the associated
+   * y-offset so the panel can open fully on-screen. If it still won't fit,
+   * sets the offset back to 0 to allow the fallback position to take over.
+   */
+  private _checkOverlayWithinViewport(maxScroll: number): void {
+    const viewportRect = this._viewportRuler.getViewportRect();
+    const triggerRect = this._getTriggerRect();
+
+    const topSpaceAvailable =
+        triggerRect.top - viewportRect.top - SELECT_PANEL_VIEWPORT_PADDING;
+    const bottomSpaceAvailable =
+        viewportRect.bottom - triggerRect.bottom - SELECT_PANEL_VIEWPORT_PADDING;
+
+    const panelHeightTop = Math.abs(this._offsetY);
+    const totalPanelHeight =
+        Math.min(this.options.length * SELECT_OPTION_HEIGHT, SELECT_PANEL_MAX_HEIGHT);
+    const panelHeightBottom = totalPanelHeight -  panelHeightTop - triggerRect.height;
+
+    if (panelHeightBottom > bottomSpaceAvailable) {
+      this._adjustPanelUp(panelHeightBottom, bottomSpaceAvailable);
+    } else if (panelHeightTop > topSpaceAvailable) {
+     this._adjustPanelDown(panelHeightTop, topSpaceAvailable, maxScroll);
+    } else {
+      this._transformOrigin = this._getOriginBasedOnOption();
+    }
+  }
+
+  /** Adjusts the overlay panel up to fit in the viewport. */
+  private _adjustPanelUp(panelHeightBottom: number, bottomSpaceAvailable: number) {
+    const distanceBelowViewport = panelHeightBottom - bottomSpaceAvailable;
+
+    // Scrolls the panel up by the distance it was extending past the boundary, then
+    // adjusts the offset by that amount to move the panel up into the viewport.
+    this._scrollTop -= distanceBelowViewport;
+    this._offsetY -= distanceBelowViewport;
+    this._transformOrigin = this._getOriginBasedOnOption();
+
+    // If the panel is scrolled to the very top, it won't be able to fit the panel
+    // by scrolling, so set the offset to 0 to allow the fallback position to take
+    // effect.
+    if (this._scrollTop <= 0) {
+      this._scrollTop = 0;
+      this._offsetY = 0;
+      this._transformOrigin = `50% bottom 0px`;
+    }
+  }
+
+  /** Adjusts the overlay panel down to fit in the viewport. */
+  private _adjustPanelDown(panelHeightTop: number, topSpaceAvailable: number,
+                           maxScroll: number) {
+    const distanceAboveViewport = panelHeightTop - topSpaceAvailable;
+
+    // Scrolls the panel down by the distance it was extending past the boundary, then
+    // adjusts the offset by that amount to move the panel down into the viewport.
+    this._scrollTop += distanceAboveViewport;
+    this._offsetY += distanceAboveViewport;
+    this._transformOrigin = this._getOriginBasedOnOption();
+
+    // If the panel is scrolled to the very bottom, it won't be able to fit the
+    // panel by scrolling, so set the offset to 0 to allow the fallback position
+    // to take effect.
+    if (this._scrollTop >= maxScroll) {
+      this._scrollTop = maxScroll;
+      this._offsetY = 0;
+      this._transformOrigin = `50% top 0px`;
+      return;
+    }
+  }
+
+  /** Sets the transform origin point based on the selected option. */
+  private _getOriginBasedOnOption(): string {
+    const originY =
+        Math.abs(this._offsetY) - SELECT_OPTION_HEIGHT_ADJUSTMENT + SELECT_OPTION_HEIGHT / 2;
+    return `50% ${originY}px 0px`;
+  }
+
+}
+
+/** Clamps a value n between min and max values. */
+function clampValue(min: number, n: number, max: number): number {
+  return Math.min(Math.max(min, n), max);
 }