feat: add simplified checkbox component for usage in other components

Adds the `md-pseudo-checkbox`, which is a simplified version of `md-checkbox`, that doesn't have the expensive SVG animations or the form control logic. This will be useful for multiple selection in `md-select`, as well as other components in the future.

Relates to #2412.

Author: crisbeto

src/lib/checkbox/checkbox.scss

@@ -1,26 +1,21 @@
 @import '../core/theming/theming';
 @import '../core/style/elevation';
-@import '../core/style/variables';
+@import '../core/style/checkbox-variables';
 @import '../core/ripple/ripple';
 
-
-// The width/height of the checkbox element.
-$md-checkbox-size: $md-toggle-size !default;
-// The width of the line used to draw the checkmark / mixedmark.
-$md-checkbox-mark-stroke-size: 2/15 * $md-checkbox-size !default;
-// The width of the checkbox border shown when the checkbox is unchecked.
-$md-checkbox-border-width: 2px;
-// The base duration used for the majority of transitions for the checkbox.
-$md-checkbox-transition-duration: 90ms;
-// The amount of spacing between the checkbox and its label.
-$md-checkbox-item-spacing: $md-toggle-padding;
-
 // Manual calculation done on SVG
 $_md-checkbox-mark-path-length: 22.910259;
 $_md-checkbox-indeterminate-checked-easing-function: cubic-bezier(0.14, 0, 0, 1);
 
 // The ripple size of the checkbox
-$md-checkbox-ripple-size: 15px;
+$_md-checkbox-ripple-size: 15px;
+
+// The amount of spacing between the checkbox and its label.
+$_md-checkbox-item-spacing: $md-toggle-padding;
+
+// The width of the line used to draw the checkmark / mixedmark.
+$_md-checkbox-mark-stroke-size: 2 / 15 * $md-checkbox-size !default;
+
 
 // Fades in the background of the checkbox when it goes from unchecked -> {checked,indeterminate}.
 @keyframes md-checkbox-fade-in-background {
@@ -213,7 +208,7 @@ md-checkbox {
   height: $md-checkbox-size;
   line-height: 0;
   margin: auto;
-  margin-right: $md-checkbox-item-spacing;
+  margin-right: $_md-checkbox-item-spacing;
   order: 0;
   position: relative;
   vertical-align: middle;
@@ -223,7 +218,7 @@ md-checkbox {
 
   [dir='rtl'] & {
     margin: {
-      left: $md-checkbox-item-spacing;
+      left: $_md-checkbox-item-spacing;
       right: auto;
     }
   }
@@ -266,14 +261,14 @@ md-checkbox {
   stroke: {
     dashoffset: $_md-checkbox-mark-path-length;
     dasharray: $_md-checkbox-mark-path-length;
-    width: $md-checkbox-mark-stroke-size;
+    width: $_md-checkbox-mark-stroke-size;
   }
 }
 
 .md-checkbox-mixedmark {
   @extend %md-checkbox-mark;
 
-  height: floor($md-checkbox-mark-stroke-size);
+  height: floor($_md-checkbox-mark-stroke-size);
   opacity: 0;
   transform: scaleX(0) rotate(0deg);
 }
@@ -282,14 +277,14 @@ md-checkbox {
   .md-checkbox-inner-container {
     order: 1;
     margin: {
-      left: $md-checkbox-item-spacing;
+      left: $_md-checkbox-item-spacing;
       right: auto;
     }
 
     [dir='rtl'] & {
       margin: {
         left: auto;
-        right: $md-checkbox-item-spacing;
+        right: $_md-checkbox-item-spacing;
       }
     }
   }
@@ -421,10 +416,10 @@ md-checkbox {
 
 .md-checkbox-ripple {
   position: absolute;
-  left: -$md-checkbox-ripple-size;
-  top: -$md-checkbox-ripple-size;
-  right: -$md-checkbox-ripple-size;
-  bottom: -$md-checkbox-ripple-size;
+  left: -$_md-checkbox-ripple-size;
+  top: -$_md-checkbox-ripple-size;
+  right: -$_md-checkbox-ripple-size;
+  bottom: -$_md-checkbox-ripple-size;
   border-radius: 50%;
   z-index: 1;
   pointer-events: none;

src/lib/core/_core.scss

@@ -5,6 +5,7 @@
 @import 'ripple/ripple';
 @import 'option/option';
 @import 'option/option-theme';
+@import 'selection/pseudo-checkbox/pseudo-checkbox-theme';
 
 // Mixin that renders all of the core styles that are not theme-dependent.
 @mixin md-core() {
@@ -27,6 +28,7 @@
 @mixin md-core-theme($theme) {
   @include md-ripple-theme($theme);
   @include md-option-theme($theme);
+  @include md-pseudo-checkbox-theme($theme);
 
   // Wrapper element that provides the theme background when the
   // user's content isn't inside of a `md-sidenav-container`.

src/lib/core/core.ts

@@ -7,6 +7,7 @@ import {MdRippleModule} from './ripple/ripple';
 import {PortalModule} from './portal/portal-directives';
 import {OverlayModule} from './overlay/overlay-directives';
 import {A11yModule} from './a11y/index';
+import {MdSelectionModule} from './selection/index';
 
 
 // RTL
@@ -114,6 +115,9 @@ export * from './compatibility/default-mode';
 // Animation
 export * from './animation/animation';
 
+// Selection
+export * from './selection/index';
+
 // Coercion
 export {coerceBooleanProperty} from './coercion/boolean-property';
 export {coerceNumberProperty} from './coercion/number-property';
@@ -132,7 +136,8 @@ export {NoConflictStyleCompatibilityMode} from './compatibility/no-conflict-mode
     PortalModule,
     OverlayModule,
     A11yModule,
-    MdOptionModule
+    MdOptionModule,
+    MdSelectionModule
   ],
   exports: [
     MdLineModule,
@@ -142,7 +147,8 @@ export {NoConflictStyleCompatibilityMode} from './compatibility/no-conflict-mode
     PortalModule,
     OverlayModule,
     A11yModule,
-    MdOptionModule
+    MdOptionModule,
+    MdSelectionModule
   ],
 })
 export class MdCoreModule {

src/lib/core/selection/index.ts

@@ -0,0 +1,10 @@
+import {NgModule} from '@angular/core';
+import {MdPseudoCheckbox} from './pseudo-checkbox/pseudo-checkbox';
+
+export * from './pseudo-checkbox/pseudo-checkbox';
+
+@NgModule({
+  exports: [MdPseudoCheckbox],
+  declarations: [MdPseudoCheckbox]
+})
+export class MdSelectionModule { }

src/lib/core/selection/pseudo-checkbox/_pseudo-checkbox-theme.scss

@@ -0,0 +1,44 @@
+@import '../../theming/theming';
+
+
+@mixin md-pseudo-checkbox-theme($theme) {
+  $is-dark-theme: map-get($theme, is-dark);
+  $primary: map-get($theme, primary);
+  $accent: map-get($theme, accent);
+  $warn: map-get($theme, warn);
+  $background: map-get($theme, background);
+
+  // The color of the checkbox's checkmark / mixedmark.
+  $checkbox-mark-color: md-color($background, background);
+
+  // NOTE(traviskaufman): While the spec calls for translucent blacks/whites for disabled colors,
+  // this does not work well with elements layered on top of one another. To get around this we
+  // blend the colors together based on the base color and the theme background.
+  $white-30pct-opacity-on-dark: #686868;
+  $black-26pct-opacity-on-light: #b0b0b0;
+  $disabled-color: if($is-dark-theme, $white-30pct-opacity-on-dark, $black-26pct-opacity-on-light);
+
+  md-pseudo-checkbox::after {
+    color: $checkbox-mark-color;
+  }
+
+  .md-pseudo-checkbox-checked, .md-pseudo-checkbox-indeterminate {
+    border: none;
+
+    &.md-primary {
+      background: md-color($primary, 500);
+    }
+
+    &.md-accent {
+      background: md-color($accent, 500);
+    }
+
+    &.md-warn {
+      background: md-color($warn, 500);
+    }
+
+    &.md-pseudo-checkbox-disabled {
+      background: $disabled-color;
+    }
+  }
+}

src/lib/core/selection/pseudo-checkbox/pseudo-checkbox.html

@@ -0,0 +1,52 @@
+@import '../../style/checkbox-variables';
+
+// Padding inside of a pseudo checkbox.
+$_md-pseudo-checkbox-padding: $md-checkbox-border-width * 2;
+
+// Size of the checkmark in a pseudo checkbox.
+$_md-pseudo-checkmark-size: $md-checkbox-size - (2 * $_md-pseudo-checkbox-padding);
+
+
+md-pseudo-checkbox {
+  width: $md-checkbox-size;
+  height: $md-checkbox-size;
+  border: $md-checkbox-border-width solid;
+  border-radius: 2px;
+  cursor: pointer;
+  display: inline-block;
+  vertical-align: middle;
+  box-sizing: border-box;
+  position: relative;
+  transition:
+      border-color $md-checkbox-transition-duration $md-linear-out-slow-in-timing-function,
+      background-color $md-checkbox-transition-duration $md-linear-out-slow-in-timing-function;
+
+  &::after {
+    position: absolute;
+    opacity: 0;
+    content: "";
+    border-bottom: $md-checkbox-border-width solid currentColor;
+    transition: opacity $md-checkbox-transition-duration $md-linear-out-slow-in-timing-function;
+  }
+}
+
+.md-pseudo-checkbox-disabled {
+  cursor: default;
+}
+
+.md-pseudo-checkbox-indeterminate::after {
+  top: ($md-checkbox-size - $md-checkbox-border-width) / 2;
+  left: $md-checkbox-border-width;
+  width: $md-checkbox-size - ($md-checkbox-border-width * 2);
+  opacity: 1;
+}
+
+.md-pseudo-checkbox-checked::after {
+  top: ($md-checkbox-size / 2) - ($_md-pseudo-checkmark-size / 4) - ($md-checkbox-size / 10);
+  left: $_md-pseudo-checkbox-padding - $md-checkbox-border-width / 2;
+  width: $_md-pseudo-checkmark-size;
+  height: ($_md-pseudo-checkmark-size - $md-checkbox-border-width) / 2;
+  border-left: $md-checkbox-border-width solid currentColor;
+  transform: rotate(-45deg);
+  opacity: 1;
+}

src/lib/core/selection/pseudo-checkbox/pseudo-checkbox.scss

@@ -0,0 +1,53 @@
+import {
+  Component,
+  ViewEncapsulation,
+  Input,
+  ElementRef,
+  Renderer,
+} from '@angular/core';
+
+export type MdPseudoCheckboxState = 'unchecked' | 'checked' | 'indeterminate';
+
+/**
+ * Simplified checkbox without any of the underlying form control logic
+ * and fancy animations. To be used when composing other components.
+ * @docs-private
+ */
+@Component({
+  moduleId: module.id,
+  encapsulation: ViewEncapsulation.None,
+  selector: 'md-pseudo-checkbox',
+  styleUrls: ['pseudo-checkbox.css'],
+  templateUrl: 'pseudo-checkbox.html',
+  host: {
+    '[class.md-pseudo-checkbox-indeterminate]': 'state === "indeterminate"',
+    '[class.md-pseudo-checkbox-checked]': 'state === "checked"',
+    '[class.md-pseudo-checkbox-disabled]': 'disabled',
+  },
+})
+export class MdPseudoCheckbox {
+  /** Display state of the checkbox. */
+  @Input() state: MdPseudoCheckboxState = 'unchecked';
+
+  /** Whether the checkbox is disabled. */
+  @Input() disabled: boolean = false;
+
+  /** Color of the checkbox. */
+  @Input()
+  get color(): string { return this._color; };
+  set color(value: string) {
+    if (value) {
+      let nativeElement = this._elementRef.nativeElement;
+
+      this._renderer.setElementClass(nativeElement, `md-${this.color}`, false);
+      this._renderer.setElementClass(nativeElement, `md-${value}`, true);
+      this._color = value;
+    }
+  }
+
+  private _color: string;
+
+  constructor(private _elementRef: ElementRef, private _renderer: Renderer) {
+    this.color = 'accent';
+  }
+}

src/lib/core/selection/pseudo-checkbox/pseudo-checkbox.ts

@@ -0,0 +1,10 @@
+@import './variables';
+
+// The width/height of the checkbox element.
+$md-checkbox-size: $md-toggle-size !default;
+
+// The width of the checkbox border shown when the checkbox is unchecked.
+$md-checkbox-border-width: 2px;
+
+// The base duration used for the majority of transitions for the checkbox.
+$md-checkbox-transition-duration: 90ms;