Re-introduce lazy loading #2367

docs/userGuide/syntax/annotations.md

@@ -14,7 +14,7 @@ The x and y coordinates of each Annotate Point are relative to the image and are
 <variable name="highlightStyle">html</variable>
 <variable name="code">
 
-<annotate src="../../images/annotateSampleImage.png" width="500" alt="Sample Image">
+<annotate src="../../images/annotateSampleImage.png" width="500" alt="Sample Image" lazy>
   <!-- Minimal Point -->
   <a-point x="25%" y="25%" content="This point is 25% from the left and 25% from the top" />
   <!-- Customize Point Size (default size is 40px) -->
@@ -191,11 +191,12 @@ Here we showcase some use cases of the Annotate feature.
 This is effectively the same as the options used for the [picture](#pictures) component.
 
 | Name   | Type      | Default | Description                                                                                                                                                                                                           |
-| ------ | --------- | ------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+|--------| --------- | ------- |-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | alt    | `string`  |         | **This must be specified.**<br>The alternative text of the image.                                                                                                                                                     |
 | src    | `string`  |         | **This must be specified.**<br>The URL of the image.<br>The URL can be specified as absolute or relative references. More info in: _[Intra-Site Links]({{baseUrl}}/userGuide/formattingContents.html#intraSiteLinks)_ |
 | height | `string`  |`''`| The height of the image in pixels.                                                                                                                                                                                    |
 | width  | `string`  |`''`| The width of the image in pixels.<br>If both width and height are specified, width takes priority over height. It is to maintain the image's aspect ratio.                                                            |
+| lazy   | `boolean` | false | The `<annotate>` component lazy loads if this attribute is specified.<br>**Either the height or width should be specified to avoid layout shifts while lazy loading images.**                                         |
 
 </div>
 

docs/userGuide/syntax/pictures.md

@@ -5,7 +5,7 @@
 <include src="codeAndOutput.md" boilerplate >
 <variable name="highlightStyle">html</variable>
 <variable name="code">
-<pic src="https://markbind.org/images/logo-lightbackground.png" width="300" alt="Logo">
+<pic src="https://markbind.org/images/logo-lightbackground.png" width="300" alt="Logo" lazy>
   MarkBind Logo
 </pic>
 </variable>
@@ -18,11 +18,12 @@ alt | `string` | | **This must be specified.**<br>The alternative text of the im
 height | `string` | | The height of the image in pixels.
 src | `string` | | **This must be specified.**<br>The URL of the image.<br>The URL can be specified as absolute or relative references. More info in: _[Intra-Site Links]({{baseUrl}}/userGuide/formattingContents.html#intraSiteLinks)_
 width | `string` | | The width of the image in pixels.<br>If both width and height are specified, width takes priority over height. It is to maintain the image's aspect ratio.
+lazy | `boolean` | false | The `<pic>` component lazy loads if this attribute is specified.<br>**Either the height or width should be specified to avoid layout shifts while lazy loading images.**
 
 <div id="short" class="d-none">
 
 ```html
-<pic src="https://markbind.org/images/logo-lightbackground.png" width="300" alt="Logo">
+<pic src="https://markbind.org/images/logo-lightbackground.png" width="300" alt="Logo" lazy>
   MarkBind Logo
 </pic>
 ```

packages/core/src/html/NodeProcessor.ts

@@ -265,6 +265,20 @@ export class NodeProcessor {
          */
         if (!_.has(node.attribs, 'v-pre')) { node.attribs['v-pre'] = ''; }
         break;
+      case 'pic':
+      case 'annotate':
+        if (_.has(node.attribs, 'lazy')
+            && !(_.has(node.attribs, 'width') || _.has(node.attribs, 'height'))) {
+          const filePath = context.callStack.length > 0 ? context.callStack[context.callStack.length - 1]
+            : context.cwf;
+          logger.warn(
+            `${filePath} --- `
+              + 'Both width and height are not specified when using lazy loading in the file and'
+              + ' it might cause shifting in page layouts. '
+              + 'To ensure proper functioning of lazy loading, please specify either one or both.\n',
+          );
+        }
+        break;
       default:
         break;
       }

packages/core/test/unit/html/NodeProcessor.test.ts

@@ -1,8 +1,9 @@
 import path from 'path';
 import cheerio from 'cheerio';
 import htmlparser from 'htmlparser2';
-import * as testData from './NodeProcessor.data';
+import { expect } from '@jest/globals';
 import * as logger from '../../../src/utils/logger';
+import * as testData from './NodeProcessor.data';
 import { Context } from '../../../src/html/Context';
 import { shiftSlotNodeDeeper, transformOldSlotSyntax } from '../../../src/html/vueSlotSyntaxProcessor';
 import { getNewDefaultNodeProcessor } from '../utils/utils';
@@ -139,6 +140,68 @@ test('processNode processes dropdown with header slot taking priority over heade
   expect(warnSpy).toHaveBeenCalledWith(testData.PROCESS_DROPDOWN_HEADER_SLOT_TAKES_PRIORITY_WARN_MSG);
 });
 
+test('processNode does not log warning when lazy pic has width or height',
+     () => {
+       const nodeProcessor = getNewDefaultNodeProcessor();
+
+       const testCode = '<pic scr="" alt="" width="300" lazy></pic>';
+       const testNode = parseHTML(testCode)[0] as MbNode;
+
+       const consoleSpy = jest.spyOn(logger, 'warn');
+
+       nodeProcessor.processNode(testNode, new Context(path.resolve(''), [], {}, {}));
+
+       expect(consoleSpy).not.toHaveBeenCalled();
+     });
+
+test('processNode does not log warning when lazy annotate has width or height',
+     () => {
+       const nodeProcessor = getNewDefaultNodeProcessor();
+
+       const testCode = '<annotate scr="" alt="" height="300" lazy></annotate>';
+       const testNode = parseHTML(testCode)[0] as MbNode;
+
+       const consoleSpy = jest.spyOn(logger, 'warn');
+
+       nodeProcessor.processNode(testNode, new Context(path.resolve(''), [], {}, {}));
+
+       expect(consoleSpy).not.toHaveBeenCalled();
+     });
+
+test('processNode logs warning when lazy pic no width and height',
+     () => {
+       const nodeProcessor = getNewDefaultNodeProcessor();
+
+       const testCode = '<pic scr="" alt="" lazy></pic>';
+       const testNode = parseHTML(testCode)[0] as MbNode;
+
+       const consoleSpy = jest.spyOn(logger, 'warn');
+
+       nodeProcessor.processNode(testNode, new Context('testpath.md', [], {}, {}));
+
+       expect(consoleSpy).toHaveBeenCalledWith('testpath.md --- '
+           + 'Both width and height are not specified when using lazy loading in the file and'
+           + ' it might cause shifting in page layouts. '
+           + 'To ensure proper functioning of lazy loading, please specify either one or both.\n');
+     });
+
+test('processNode logs warning when lazy annotate no width and height',
+     () => {
+       const nodeProcessor = getNewDefaultNodeProcessor();
+
+       const testCode = '<annotate scr="" alt="" lazy></annotate>';
+       const testNode = parseHTML(testCode)[0] as MbNode;
+
+       const consoleSpy = jest.spyOn(logger, 'warn');
+
+       nodeProcessor.processNode(testNode, new Context('testpath.md', [], {}, {}));
+
+       expect(consoleSpy).toHaveBeenCalledWith('testpath.md --- '
+           + 'Both width and height are not specified when using lazy loading in the file and'
+           + ' it might cause shifting in page layouts. '
+           + 'To ensure proper functioning of lazy loading, please specify either one or both.\n');
+     });
+
 test('markdown coverts inline colour syntax correctly', async () => {
   const nodeProcessor = getNewDefaultNodeProcessor();
   const indexPath = 'index.md';

packages/vue-components/src/Pic.vue

@@ -5,8 +5,10 @@
       :src="src"
       :alt="alt"
       :width="computedWidth"
+      :height="computedHeight"
+      :loading="computedLoadType"
       class="img-fluid rounded"
-      @load.once="computeWidth"
+      @load.once="computeWidthAndHeight"
     />
     <span class="image-caption">
       <slot></slot>
@@ -35,6 +37,10 @@ export default {
       type: String,
       default: '',
     },
+    lazy: {
+      type: Boolean,
+      default: false,
+    },
     addClass: {
       type: String,
       default: '',
@@ -53,20 +59,30 @@ export default {
       }
       return this.widthFromHeight;
     },
+    computedHeight() {
+      return this.heightFromWidth;
+    },
+    computedLoadType() {
+      return this.lazy ? 'lazy' : 'eager';
+    },
   },
   data() {
     return {
       widthFromHeight: '',
+      heightFromWidth: '',
     };
   },
   methods: {
-    computeWidth() {
-      if (!this.hasWidth && this.hasHeight) {
-        const renderedImg = this.$refs.pic;
-        const imgHeight = renderedImg.naturalHeight;
-        const imgWidth = renderedImg.naturalWidth;
-        const aspectRatio = imgWidth / imgHeight;
+    computeWidthAndHeight() {
+      const renderedImg = this.$refs.pic;
+      const imgHeight = renderedImg.naturalHeight;
+      const imgWidth = renderedImg.naturalWidth;
+      const aspectRatio = imgWidth / imgHeight;
+      if (this.hasWidth) { // if width is present, overwrite the height (if any) to maintain aspect ratio
+        this.heightFromWidth = Math.round(toNumber(this.width) / aspectRatio).toString();
+      } else if (this.hasHeight) {
         this.widthFromHeight = Math.round(toNumber(this.height) * aspectRatio).toString();
+        this.heightFromWidth = this.height;
       }
     },
   },

packages/vue-components/src/__tests__/__snapshots__/Annotation.spec.js.snap

@@ -6,6 +6,8 @@ exports[`Annotation with customised annotation points 1`] = `
 >
   <img
     class="annotate-image"
+    height=""
+    loading="eager"
     src="./annotateSampleImage.png"
     width=""
   />
@@ -92,6 +94,8 @@ exports[`Annotation with different visual annotation points 1`] = `
 >
   <img
     class="annotate-image"
+    height=""
+    loading="eager"
     src="./annotateSampleImage.png"
     width=""
   />
@@ -380,6 +384,8 @@ exports[`Annotation with markdown in header, content and label 1`] = `
 >
   <img
     class="annotate-image"
+    height=""
+    loading="eager"
     src="./annotateSampleImage.png"
     width=""
   />

packages/vue-components/src/annotations/Annotate.vue

@@ -5,8 +5,10 @@
       :src="src"
       :alt="alt"
       :width="computedWidth"
+      :height="computedHeight"
+      :loading="computedLoadType"
       class="annotate-image"
-      @load.once="getWidth"
+      @load.once="computeWidthAndHeight"
     />
     <div style="top: 0; left: 0; height: 0;">
       <slot></slot>
@@ -35,6 +37,10 @@ export default {
       type: String,
       default: '',
     },
+    lazy: {
+      type: Boolean,
+      default: false,
+    },
     addClass: {
       type: String,
       default: '',
@@ -53,20 +59,30 @@ export default {
       }
       return this.widthFromHeight;
     },
+    computedHeight() {
+      return this.heightFromWidth;
+    },
+    computedLoadType() {
+      return this.lazy ? 'lazy' : 'eager';
+    },
   },
   data() {
     return {
       widthFromHeight: '',
+      heightFromWidth: '',
     };
   },
   methods: {
-    getWidth() {
-      if (!this.hasWidth && this.hasHeight) {
-        const renderedImg = this.$refs.pic;
-        const imgHeight = renderedImg.naturalHeight;
-        const imgWidth = renderedImg.naturalWidth;
-        const imageAspectRatio = imgWidth / imgHeight;
-        this.widthFromHeight = Math.round(toNumber(this.height) * imageAspectRatio);
+    computeWidthAndHeight() {
+      const renderedImg = this.$refs.pic;
+      const imgHeight = renderedImg.naturalHeight;
+      const imgWidth = renderedImg.naturalWidth;
+      const aspectRatio = imgWidth / imgHeight;
+      if (this.hasWidth) { // if width is present, overwrite the height (if any) to maintain aspect ratio
+        this.heightFromWidth = Math.round(toNumber(this.width) / aspectRatio).toString();
+      } else if (this.hasHeight) {
+        this.widthFromHeight = Math.round(toNumber(this.height) * aspectRatio).toString();
+        this.heightFromWidth = this.height;
       }
     },
   },