feat: display an a11y warning when slide's colors do not meet contrast ratio

CHANGELOG.md

@@ -18,7 +18,7 @@
 ### Others
 
 - deck-utils: v2.4.0 ([CHANGELOG](https://github.com/deckgo/deckdeckgo/blob/master/utils/deck/CHANGELOG.md))
-- utils: v1.2.0 ([CHANGELOG](https://github.com/deckgo/deckdeckgo/blob/master/utils/utils/CHANGELOG.md))
+- utils: v1.3.0 ([CHANGELOG](https://github.com/deckgo/deckdeckgo/blob/master/utils/utils/CHANGELOG.md))
 - starter kit: v2.6.4 ([CHANGELOG](https://github.com/deckgo/deckdeckgo-starter/blob/master/CHANGELOG.md))
 
 <a name="2.1.0"></a>

studio/package.json

@@ -40,7 +40,7 @@
     "@deckdeckgo/slide-title": "^1.1.3",
     "@deckdeckgo/slide-youtube": "^1.1.2",
     "@deckdeckgo/social": "^2.0.0",
-    "@deckdeckgo/utils": "^1.2.0",
+    "@deckdeckgo/utils": "^1.3.0",
     "@deckdeckgo/youtube": "^1.1.2",
     "@ionic/core": "^5.3.1",
     "firebase": "^7.17.2",

studio/src/app/components/editor/app-slide-contrast/app-slide-contrast.scss

@@ -0,0 +1,40 @@
+app-slide-contrast {
+  position: absolute;
+  top: 16px;
+  left: 16px;
+
+  transition: opacity 0.5s;
+
+  visibility: initial;
+  opacity: 1;
+
+  &:not(.warning) {
+    visibility: hidden;
+    opacity: 0;
+  }
+
+  button {
+    display: flex;
+    justify-content: center;
+    align-items: center;
+
+    background: var(--ion-color-warning);
+    color: var(--ion-color-warning-contrast);
+
+    padding: 6px 12px;
+    border-radius: 64px;
+
+    position: relative;
+    overflow: hidden;
+
+    outline: 0;
+
+    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.12);
+
+    font-size: var(--font-size-small);
+
+    ion-label {
+      margin-right: 4px;
+    }
+  }
+}

studio/src/app/components/editor/app-slide-contrast/app-slide-contrast.tsx

@@ -0,0 +1,133 @@
+import {Component, h, Host, Listen, State} from '@stencil/core';
+
+import {popoverController} from '@ionic/core';
+
+import {ContrastUtils} from '../../../utils/editor/contrast.utils';
+import {NodeUtils} from '../../../utils/editor/node.utils';
+
+@Component({
+  tag: 'app-slide-contrast',
+  styleUrl: 'app-slide-contrast.scss',
+})
+export class AppSlideContrast {
+  private readonly lowestAACompliantLevel: number = 3;
+
+  @State()
+  private warning: boolean = false;
+
+  @Listen('slidesDidLoad', {target: 'document'})
+  async onSlidesDidLoad() {
+    await this.analyzeContrast();
+  }
+
+  @Listen('slideDidUpdate', {target: 'document'})
+  async onSlideDidUpdate() {
+    await this.analyzeContrast();
+  }
+
+  @Listen('deckDidChange', {target: 'document'})
+  async onDeckDidChange() {
+    await this.analyzeContrast();
+  }
+
+  @Listen('slideNextDidChange', {target: 'document'})
+  @Listen('slidePrevDidChange', {target: 'document'})
+  @Listen('slideToChange', {target: 'document'})
+  async onSlideNavigate() {
+    await this.analyzeContrast();
+  }
+
+  private async analyzeContrast() {
+    this.warning = await this.hasLowContrast();
+  }
+
+  private async hasLowContrast(): Promise<boolean> {
+    const deck: HTMLElement = document.querySelector('main > deckgo-deck');
+
+    if (!deck) {
+      return false;
+    }
+
+    const index = await (deck as any).getActiveIndex();
+
+    const slide: HTMLElement = deck.querySelector('.deckgo-slide-container:nth-child(' + (index + 1) + ')');
+
+    if (!slide) {
+      return false;
+    }
+
+    const slots: NodeListOf<HTMLElement> = slide.querySelectorAll(
+      '[slot="title"]:not(:empty),[slot="content"]:not(:empty),[slot="start"]:not(:empty),[slot="end"]:not(:empty),[slot="header"]:not(:empty),[slot="footer"]:not(:empty),[slot="author"]:not(:empty),deckgo-drr > section:not(:empty)'
+    );
+
+    if (!slots || slots.length <= 0) {
+      return false;
+    }
+
+    // Slots with direct text children
+    const slotsWithText: HTMLElement[] = await NodeUtils.childrenTextNode(slots);
+
+    // All children (<span/>) of the slots
+    const children: HTMLElement[] = await NodeUtils.children(slots);
+
+    const elements: HTMLElement[] =
+      children && children.length > 0
+        ? slotsWithText && slotsWithText.length > 0
+          ? [...Array.from(slotsWithText), ...children]
+          : [...children]
+        : slotsWithText && slotsWithText.length > 0
+        ? [...slotsWithText]
+        : null;
+
+    if (!elements) {
+      return false;
+    }
+
+    const promises: Promise<number>[] = Array.from(elements).map((element: HTMLElement) => this.calculateRatio(element, deck, slide));
+
+    const contrasts: number[] = await Promise.all(promises);
+
+    if (!contrasts || contrasts.length <= 0) {
+      return false;
+    }
+
+    const lowContrast: number | undefined = contrasts.find((contrast: number) => contrast < this.lowestAACompliantLevel);
+
+    return lowContrast !== undefined;
+  }
+
+  private async calculateRatio(element: HTMLElement, deck: HTMLElement, slide: HTMLElement) {
+    const bgColor = await NodeUtils.findColors(element, 'background', deck, slide);
+    const color = await NodeUtils.findColors(element, 'color', deck, slide);
+
+    console.log('yo', bgColor, color);
+
+    return ContrastUtils.calculateContrastRatio(bgColor, color);
+  }
+
+  private async openInformation($event: UIEvent) {
+    const popover: HTMLIonPopoverElement = await popoverController.create({
+      component: 'app-contrast-info',
+      event: $event,
+      mode: 'ios',
+      cssClass: 'info',
+    });
+
+    await popover.present();
+  }
+
+  render() {
+    return (
+      <Host
+        class={{
+          warning: this.warning,
+        }}>
+        <button class="ion-activatable" onClick={($event: UIEvent) => this.openInformation($event)}>
+          <ion-ripple-effect></ion-ripple-effect>
+          <ion-label>Low contrast</ion-label>
+          <ion-icon name="warning-outline"></ion-icon>
+        </button>
+      </Host>
+    );
+  }
+}

studio/src/app/pages/editor/app-editor/app-editor.tsx

@@ -652,6 +652,7 @@ export class AppEditor {
             {this.footer}
           </deckgo-deck>
           <deckgo-remote autoConnect={false}></deckgo-remote>
+          <app-slide-contrast></app-slide-contrast>
         </main>
       </ion-content>,
       <ion-footer class={this.presenting ? 'idle' : undefined}>

studio/src/app/popovers/editor/app-contrast-info/app-contrast-info.tsx

@@ -0,0 +1,35 @@
+import {Component, Element, h} from '@stencil/core';
+
+@Component({
+  tag: 'app-contrast-info',
+})
+export class AppContrastInfo {
+  @Element() el: HTMLElement;
+
+  private async closePopover() {
+    await (this.el.closest('ion-popover') as HTMLIonPopoverElement).dismiss();
+  }
+
+  render() {
+    return (
+      <div class="ion-padding">
+        <h2>Low contrast</h2>
+        <p>We noticed that (a part of) the text color of this slide does not meet contrast ratio standards.</p>
+        <p>
+          Elements are compared according{' '}
+          <a href="https://www.w3.org/TR/WCAG/#contrast-minimum" target="_blank" rel="noopener noreferrer">
+            WCAG
+          </a>{' '}
+          Level AA.
+        </p>
+
+        <p>Note that if you are using semi-transparent background, the contrast ratio cannot be precise.</p>
+        <div class="ion-text-center">
+          <ion-button size="small" shape="round" color="primary" onClick={() => this.closePopover()}>
+            Got it
+          </ion-button>
+        </div>
+      </div>
+    );
+  }
+}

studio/src/app/popovers/editor/app-get-help/app-get-help.tsx

@@ -29,7 +29,7 @@ export class AppGetHelp {
           </a>
           .
         </p>
-        <div class="ion-text-center ion-padding-top">
+        <div class="ion-text-center">
           <ion-button size="small" shape="round" color="primary" onClick={() => this.closePopover()}>
             Got it
           </ion-button>

studio/src/app/utils/editor/contrast.utils.tsx

@@ -0,0 +1,110 @@
+import {extractRgb, extractRgba} from '@deckdeckgo/utils';
+
+export class ContrastUtils {
+  static async calculateContrastRatio(bgColor: string | undefined, color: string | undefined): Promise<number> {
+    const bgColorWithDefault: string = bgColor === undefined || bgColor === '' ? `rgb(255, 255, 255)` : bgColor;
+    const colorWithDefault: string = color === undefined || color === '' ? `rgb(0, 0, 0)` : color;
+
+    // The text color may or may not be semi-transparent, but that doesn't matter
+    const bgRgba: number[] | undefined = extractRgba(bgColorWithDefault);
+
+    if (!bgRgba || bgRgba.length < 4 || bgRgba[3] >= 1) {
+      return this.calculateContrastRatioOpaque(bgColorWithDefault, colorWithDefault);
+    }
+
+    return this.calculateContrastRatioAlpha(bgColorWithDefault, colorWithDefault);
+  }
+
+  private static calculateLuminance(rgb: number[]): number {
+    const a = rgb.map((v) => {
+      v /= 255;
+      return v <= 0.03928 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, 2.4);
+    });
+    return a[0] * 0.2126 + a[1] * 0.7152 + a[2] * 0.0722;
+  }
+
+  private static calculateColorContrastRatio(firstColorLum: number, secondColorLum: number): number {
+    // return firstColorLum > secondColorLum ? (secondColorLum + 0.05) / (firstColorLum + 0.05) : (firstColorLum + 0.05) / (secondColorLum + 0.05);
+
+    const l1 = firstColorLum + 0.05;
+    const l2 = secondColorLum + 0.05;
+
+    let ratio = l1 / l2;
+
+    if (l2 > l1) {
+      ratio = 1 / ratio;
+    }
+
+    return ratio;
+  }
+
+  // Source: https://github.com/LeaVerou/contrast-ratio/blob/eb7fe8f16206869f8d36d517d7eb0962830d0e81/color.js#L86
+  private static async convertAlphaRgba(color: string, base: number[]): Promise<string> {
+    const rgba: number[] | undefined = extractRgba(color);
+
+    if (!rgba || rgba.length < 4) {
+      return color;
+    }
+
+    const alpha: number = rgba[3];
+
+    const rgb: number[] = [];
+
+    for (let i = 0; i < 3; i++) {
+      rgb.push(rgba[i] * alpha + base[i] * base[3] * (1 - alpha));
+    }
+
+    // Not used here
+    // rgb[3] = alpha + base[3] * (1 - alpha);
+
+    return `rgb(${rgb[0]}, ${rgb[1]}, ${rgb[2]})`;
+  }
+
+  private static async calculateColorContrastRatioWithBase(
+    bgColor: string,
+    lumColor: number,
+    base: number[]
+  ): Promise<{luminanceOverlay: number; ratio: number}> {
+    const overlay = extractRgb(await this.convertAlphaRgba(bgColor, base));
+
+    const lumOverlay: number = this.calculateLuminance(overlay);
+
+    return {
+      luminanceOverlay: lumOverlay,
+      ratio: this.calculateColorContrastRatio(lumOverlay, lumColor),
+    };
+  }
+
+  private static async calculateContrastRatioAlpha(bgColor: string, color: string): Promise<number> {
+    const lumColor: number = this.calculateLuminance(extractRgb(color));
+
+    const onBlack: {luminanceOverlay: number; ratio: number} = await this.calculateColorContrastRatioWithBase(bgColor, lumColor, [0, 0, 0, 1]);
+    const onWhite: {luminanceOverlay: number; ratio: number} = await this.calculateColorContrastRatioWithBase(bgColor, lumColor, [255, 255, 255, 1]);
+
+    const max = Math.max(onBlack.ratio, onWhite.ratio);
+
+    let min = 1;
+    if (onBlack.luminanceOverlay > lumColor) {
+      min = onBlack.ratio;
+    } else if (onWhite.luminanceOverlay < lumColor) {
+      min = onWhite.ratio;
+    }
+
+    return (min + max) / 2;
+  }
+
+  private static async calculateContrastRatioOpaque(bgColor: string, color: string): Promise<number> {
+    const bgRgb: number[] | undefined = extractRgb(bgColor);
+    const colorRgb: number[] | undefined = extractRgb(color);
+
+    if (bgColor === undefined || colorRgb === undefined) {
+      // 0 being AA and AAA level friendly. We assume that if for some reason we can't extract color, we better not display a warning about it.
+      return 0;
+    }
+
+    const lumBg: number = this.calculateLuminance(bgRgb);
+    const lumColor: number = this.calculateLuminance(colorRgb);
+
+    return this.calculateColorContrastRatio(lumBg, lumColor);
+  }
+}