refactor(common): request low quality placeholder images

For every built-in load, this commit adds a parameter to load low quality placeholder images. Using 20/100 as base value.

packages/common/src/directives/ng_optimized_image/image_loaders/cloudflare_loader.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {PLACEHOLDER_QUALITY} from './constants';
 import {createImageLoader, ImageLoaderConfig} from './image_loader';
 
 /**
@@ -29,6 +30,12 @@ function createCloudflareUrl(path: string, config: ImageLoaderConfig) {
   if (config.width) {
     params += `,width=${config.width}`;
   }
+
+  // When requesting a placeholder image we ask for a low quality image to reduce the load time.
+  if (config.isPlaceholder) {
+    params += `,quality=${PLACEHOLDER_QUALITY}`;
+  }
+
   // Cloudflare image URLs format:
   // https://developers.cloudflare.com/images/image-resizing/url-format/
   return `${path}/cdn-cgi/image/${params}/${config.src}`;

packages/common/src/directives/ng_optimized_image/image_loaders/cloudinary_loader.ts

@@ -52,9 +52,15 @@ function createCloudinaryUrl(path: string, config: ImageLoaderConfig) {
   // https://cloudinary.com/documentation/image_transformations#transformation_url_structure
   // Example of a Cloudinary image URL:
   // https://res.cloudinary.com/mysite/image/upload/c_scale,f_auto,q_auto,w_600/marketing/tile-topics-m.png
-  let params = `f_auto,q_auto`; // sets image format and quality to "auto"
+
+  // For a placeholder image, we use the lowest image setting available to reduce the load time
+  // else we use the auto size
+  const quality = config.isPlaceholder ? 'q_auto:low' : 'q_auto';
+
+  let params = `f_auto,${quality}`;
   if (config.width) {
     params += `,w_${config.width}`;
   }
+
   return `${path}/image/upload/${params}/${config.src}`;
 }

packages/common/src/directives/ng_optimized_image/image_loaders/constants.ts

@@ -0,0 +1,12 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/**
+ * Value (out of 100) of the requested quality for placeholder images.
+ */
+export const PLACEHOLDER_QUALITY = '20';

packages/common/src/directives/ng_optimized_image/image_loaders/imagekit_loader.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {PLACEHOLDER_QUALITY} from './constants';
 import {createImageLoader, ImageLoaderConfig, ImageLoaderInfo} from './image_loader';
 
 /**
@@ -53,5 +54,11 @@ export function createImagekitUrl(path: string, config: ImageLoaderConfig): stri
     urlSegments = [path, src];
   }
 
-  return urlSegments.join('/');
+  const url = new URL(urlSegments.join('/'));
+
+  // When requesting a placeholder image we ask for a low quality image to reduce the load time.
+  if (config.isPlaceholder) {
+    url.searchParams.set('q', PLACEHOLDER_QUALITY);
+  }
+  return url.href;
 }

packages/common/src/directives/ng_optimized_image/image_loaders/imgix_loader.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {PLACEHOLDER_QUALITY} from './constants';
 import {createImageLoader, ImageLoaderConfig, ImageLoaderInfo} from './image_loader';
 
 /**
@@ -45,5 +46,10 @@ function createImgixUrl(path: string, config: ImageLoaderConfig) {
   if (config.width) {
     url.searchParams.set('w', config.width.toString());
   }
+
+  // When requesting a placeholder image we ask a low quality image to reduce the load time.
+  if (config.isPlaceholder) {
+    url.searchParams.set('q', PLACEHOLDER_QUALITY);
+  }
   return url.href;
 }

packages/common/src/directives/ng_optimized_image/image_loaders/netlify_loader.ts

@@ -16,6 +16,7 @@ import {RuntimeErrorCode} from '../../../errors';
 import {isAbsoluteUrl, isValidPath} from '../url';
 
 import {IMAGE_LOADER, ImageLoaderConfig, ImageLoaderInfo} from './image_loader';
+import {PLACEHOLDER_QUALITY} from './constants';
 
 /**
  * Name and URL tester for Netlify.
@@ -90,6 +91,13 @@ function createNetlifyUrl(config: ImageLoaderConfig, path?: string) {
     url.searchParams.set('w', config.width.toString());
   }
 
+  // When requesting a placeholder image we ask for a low quality image to reduce the load time.
+  // If the quality is specified in the loader config - always use provided value.
+  const configQuality = config.loaderParams?.['quality'] ?? config.loaderParams?.['q'];
+  if (config.isPlaceholder && !configQuality) {
+    url.searchParams.set('q', PLACEHOLDER_QUALITY);
+  }
+
   for (const [param, value] of Object.entries(config.loaderParams ?? {})) {
     if (validParams.has(param)) {
       url.searchParams.set(validParams.get(param)!, value.toString());

packages/common/test/image_loaders/image_loader_spec.ts

@@ -75,6 +75,13 @@ describe('Built-in image directive loaders', () => {
       const loader = createImgixLoader(path);
       expect(() => loader({src})).toThrowError(absoluteUrlError(src, path));
     });
+
+    it('should load a low quality image when a placeholder is requested', () => {
+      const path = 'https://somesite.imgix.net';
+      const loader = createImgixLoader(path);
+      const config = {src: 'img.png', isPlaceholder: true};
+      expect(loader(config)).toBe(`${path}/img.png?auto=format&q=20`);
+    });
   });
 
   describe('Cloudinary loader', () => {
@@ -97,6 +104,13 @@ describe('Built-in image directive loaders', () => {
       ).toBe(`${path}/image/upload/f_auto,q_auto/marketing/img-2.png`);
     });
 
+    it('should load a low quality image when a placeholder is requested', () => {
+      const path = 'https://res.cloudinary.com/mysite';
+      const loader = createCloudinaryLoader(path);
+      const config = {src: 'img.png', isPlaceholder: true};
+      expect(loader(config)).toBe(`${path}/image/upload/f_auto,q_auto:low/img.png`);
+    });
+
     describe('input validation', () => {
       it('should throw if an absolute URL is provided as a loader input', () => {
         const path = 'https://res.cloudinary.com/mysite';
@@ -154,6 +168,13 @@ describe('Built-in image directive loaders', () => {
       );
     });
 
+    it('should load a low quality image when a placeholder is requested', () => {
+      const path = 'https://ik.imageengine.io/imagetest';
+      const loader = createImageKitLoader(path);
+      const config = {src: 'img.png', isPlaceholder: true};
+      expect(loader(config)).toBe(`${path}/img.png?q=20`);
+    });
+
     describe('input validation', () => {
       it('should throw if an absolute URL is provided as a loader input', () => {
         const path = 'https://ik.imageengine.io/imagetest';
@@ -210,6 +231,15 @@ describe('Built-in image directive loaders', () => {
       const loader = createCloudflareLoader(path);
       expect(() => loader({src})).toThrowError(absoluteUrlError(src, path));
     });
+
+    it('should load a low quality image when a placeholder is requested', () => {
+      const path = 'https://mysite.com';
+      const loader = createCloudflareLoader(path);
+      const config = {src: 'img.png', isPlaceholder: true};
+      expect(loader(config)).toBe(
+        'https://mysite.com/cdn-cgi/image/format=auto,quality=20/img.png',
+      );
+    });
   });
 
   describe('Netlify loader', () => {
@@ -261,6 +291,20 @@ describe('Built-in image directive loaders', () => {
         `NG0${RuntimeErrorCode.INVALID_LOADER_ARGUMENTS}: The Netlify image loader has detected an \`<img>\` tag with the unsupported attribute "\`unknown\`".`,
       );
     });
+
+    it('should load a low quality image when a placeholder is requested', () => {
+      const path = 'https://mysite.com';
+      const loader = createNetlifyLoader(path);
+      const config = {src: 'img.png', isPlaceholder: true};
+      expect(loader(config)).toBe('https://mysite.com/.netlify/images?url=%2Fimg.png&q=20');
+    });
+
+    it('should not load a low quality image when a placeholder is requested with a quality param', () => {
+      const path = 'https://mysite.com';
+      const loader = createNetlifyLoader(path);
+      const config = {src: 'img.png', isPlaceholder: true, loaderParams: {quality: 50}};
+      expect(loader(config)).toBe('https://mysite.com/.netlify/images?url=%2Fimg.png&q=50');
+    });
   });
 
   describe('loader utils', () => {