feat: rehype-image-size, prevent image jump

lib/rehype-image-size.js

@@ -0,0 +1,36 @@
+const memoize = require('micro-memoize');
+const visit = require('unist-util-visit');
+const pAll = require('p-all');
+const sizeOf = require('image-size');
+
+/**
+ * Simple plugin to get the size of local images so we can use it in react
+ */
+const rehypeImageSize = () => {
+  async function transformer(tree) {
+    const nodes = [];
+    visit(tree, 'element', node => {
+      if (node.tagName !== 'img') {
+        return;
+      } else {
+        nodes.push(node);
+      }
+    });
+    await pAll(
+      nodes.map(node => () => visitor(node)),
+      { concurrency: 25 }
+    );
+    return tree;
+  }
+  async function visitor(node) {
+    const isRelative =
+      node && node.properties && node.properties.src && node.properties.src.startsWith('/');
+    if (isRelative) {
+      const dimensions = sizeOf(`public/${node.properties.src}`);
+      node.properties['dimensions'] = dimensions;
+    }
+  }
+  return transformer;
+};
+
+module.exports = memoize(rehypeImageSize);

lib/rehype-plugins.js

@@ -1,6 +1,7 @@
 const memoize = require('micro-memoize');
 const { rehypeVscode } = require('unified-vscode');
+const rehypeImgs = require('./rehype-image-size');
 
-const rehypePlugins = [memoize(rehypeVscode)];
+const rehypePlugins = [memoize(rehypeVscode), rehypeImgs];
 
 module.exports = { rehypePlugins };

package.json

@@ -32,6 +32,7 @@
     "gray-matter": "^4.0.2",
     "hast-util-to-string": "^1.0.4",
     "html-react-parser": "^0.13.0",
+    "image-size": "^0.8.3",
     "lodash.debounce": "^4.0.8",
     "mdi-react": "7.3.0",
     "micro-memoize": "^4.0.9",

src/components/mdx/image.tsx

@@ -40,15 +40,49 @@ const useImgix = (src: string) => {
   };
 };
 
-export const Img: React.FC<BoxProps & { loading?: string; src?: string; alt?: string }> = ({
-  src: _src,
-  ...rest
-}) => {
+const getAspectRatio = dimensions => {
+  if (!dimensions) return;
+
+  const { width, height } = dimensions;
+
+  return (height / width) * 100;
+};
+
+const BaseImg: React.FC<any> = props => (
+  <Box
+    loading="lazy"
+    maxWidth="100%"
+    width={['100%', '100%', 'inherit', 'inherit']}
+    display="block"
+    as="img"
+    {...props}
+  />
+);
+
+export const Img: React.FC<
+  BoxProps & { loading?: string; src?: string; alt?: string; dimensions?: any }
+> = React.memo(({ src: _src, dimensions, ...rest }) => {
   const { src, srcset } = useImgix(_src);
   const props = {
     src,
     srcSet: srcset,
     ...rest,
   };
-  return <Box loading="lazy" maxWidth="100%" display="block" as="img" {...props} />;
-};
+
+  if (dimensions) {
+    // means the image is local and we can generate the aspect ratio
+    // and prevent the page from jumping due to lack of an image being loaded
+    // (because of the built in lazy-loading)
+
+    const aspectRatio = getAspectRatio(dimensions);
+
+    const width = dimensions.width <= 720 ? dimensions.width : '100%';
+    return (
+      <Box width={width} maxWidth="100%" padding="0 !important" position="relative" className="img">
+        <Box height="0" paddingBottom={`${aspectRatio}%`} width="100%" />
+        <BaseImg position="absolute" top={0} left={0} {...props} />
+      </Box>
+    );
+  }
+  return <BaseImg className="img" {...props} />;
+});

src/components/mdx/md-contents.tsx

@@ -38,7 +38,7 @@ export const styleOverwrites = {
     pre: {
       // px: space(['none', 'none', 'extra-loose', 'extra-loose']),
     },
-    img: {
+    '.img': {
       mx: 'auto',
     },
   },
@@ -210,7 +210,7 @@ export const styleOverwrites = {
       mt: space('extra-loose'),
     },
   },
-  img: {
+  '.img': {
     my: space('extra-loose'),
   },
   table: {

yarn.lock

@@ -4960,6 +4960,13 @@ ignore@^4.0.6:
   resolved "https://registry.yarnpkg.com/ignore/-/ignore-4.0.6.tgz#750e3db5862087b4737ebac8207ffd1ef27b25fc"
   integrity sha512-cyFDKrqc/YdcWFniJhzI42+AzS+gNwmUzOSFcRCQYwySuBBBy/KjuxWLZ/FHEH6Moq1NizMOBWyTcv8O4OZIMg==
 
+image-size@^0.8.3:
+  version "0.8.3"
+  resolved "https://registry.yarnpkg.com/image-size/-/image-size-0.8.3.tgz#f0b568857e034f29baffd37013587f2c0cad8b46"
+  integrity sha512-SMtq1AJ+aqHB45c3FsB4ERK0UCiA2d3H1uq8s+8T0Pf8A3W4teyBQyaFaktH6xvZqh+npwlKU7i4fJo0r7TYTg==
+  dependencies:
+    queue "6.0.1"
+
 immediate@^3.2.3:
   version "3.3.0"
   resolved "https://registry.yarnpkg.com/immediate/-/immediate-3.3.0.tgz#1aef225517836bcdf7f2a2de2600c79ff0269266"
@@ -6987,6 +6994,13 @@ querystring@0.2.0, querystring@^0.2.0:
   resolved "https://registry.yarnpkg.com/querystring/-/querystring-0.2.0.tgz#b209849203bb25df820da756e747005878521620"
   integrity sha1-sgmEkgO7Jd+CDadW50cAWHhSFiA=
 
+queue@6.0.1:
+  version "6.0.1"
+  resolved "https://registry.yarnpkg.com/queue/-/queue-6.0.1.tgz#abd5a5b0376912f070a25729e0b6a7d565683791"
+  integrity sha512-AJBQabRCCNr9ANq8v77RJEv73DPbn55cdTb+Giq4X0AVnNVZvMHlYp7XlQiN+1npCZj1DuSmaA2hYVUUDgxFDg==
+  dependencies:
+    inherits "~2.0.3"
+
 randombytes@^2.0.0, randombytes@^2.0.1, randombytes@^2.0.5, randombytes@^2.1.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/randombytes/-/randombytes-2.1.0.tgz#df6f84372f0270dc65cdf6291349ab7a473d4f2a"