feat(gatsby-plugin-image): Add useArtDirection hook

packages/gatsby-plugin-image/src/components/hooks.ts

@@ -1,3 +1,4 @@
+/* eslint-disable no-unused-expressions */
 import {
   useState,
   CSSProperties,
@@ -283,3 +284,81 @@ export function useImageLoaded(
     toggleLoaded,
   }
 }
+
+export interface IArtDirectedImage {
+  media: string
+  image: IGatsbyImageData
+}
+
+/**
+ * Generate a Gatsby image data object with multiple, art-directed images that display at different
+ * resolutions.
+ *
+ * @param defaultImage The image displayed when no media query matches.
+ * It is also used for all other settings applied to the image, such as width, height and layout.
+ * You should pass a className to the component with media queries to adjust the size of the container,
+ * as this cannot be adjusted automatically.
+ * @param artDirected Array of objects which each contains a `media` string which is a media query
+ * such as `(min-width: 320px)`, and the image object to use when that query matches.
+ */
+export function useArtDirection(
+  defaultImage: IGatsbyImageData,
+  artDirected: Array<IArtDirectedImage>
+): IGatsbyImageData {
+  const { images, placeholder, ...props } = defaultImage
+  const output: IGatsbyImageData = {
+    ...props,
+    images: {
+      ...images,
+      sources: [],
+    },
+    placeholder: placeholder && {
+      ...placeholder,
+      sources: [],
+    },
+  }
+
+  artDirected.forEach(({ media, image }) => {
+    if (!media) {
+      if (process.env.NODE_ENV === `development`) {
+        console.warn(
+          "[gatsby-plugin-image] All art-directed images passed to must have a value set for `media`. Skipping."
+        )
+      }
+      return
+    }
+
+    if (
+      image.layout !== defaultImage.layout &&
+      process.env.NODE_ENV === `development`
+    ) {
+      console.warn(
+        `[gatsby-plugin-image] Mismatched image layout: expected "${defaultImage.layout}" but received "${image.layout}". All art-directed images use the same layout as the default image`
+      )
+    }
+
+    output.images.sources.push(
+      ...image.images.sources.map(source => {
+        return { ...source, media }
+      }),
+      {
+        media,
+        srcSet: image.images.fallback.srcSet,
+      }
+    )
+
+    if (!output.placeholder) {
+      return
+    }
+
+    output.placeholder.sources.push({
+      media,
+      srcSet: image.placeholder.fallback,
+    })
+  })
+  output.images.sources.push(...images.sources)
+  if (placeholder?.sources) {
+    output.placeholder?.sources.push(...placeholder.sources)
+  }
+  return output
+}

packages/gatsby-plugin-image/src/index.browser.ts

@@ -7,7 +7,13 @@ export { Placeholder } from "./components/placeholder"
 export { MainImage } from "./components/main-image"
 export { StaticImage } from "./components/static-image"
 export { LaterHydrator } from "./components/later-hydrator"
-export { getImage, getSrc, useGatsbyImage } from "./components/hooks"
+export {
+  getImage,
+  getSrc,
+  useGatsbyImage,
+  useArtDirection,
+  IArtDirectedImage,
+} from "./components/hooks"
 export {
   generateImageData,
   IGatsbyImageHelperArgs,

packages/gatsby-plugin-image/src/index.ts

@@ -6,7 +6,13 @@ export {
 export { Placeholder } from "./components/placeholder"
 export { MainImage } from "./components/main-image"
 export { StaticImage } from "./components/static-image.server"
-export { getImage, getSrc, useGatsbyImage } from "./components/hooks"
+export {
+  getImage,
+  getSrc,
+  useGatsbyImage,
+  useArtDirection,
+  IArtDirectedImage,
+} from "./components/hooks"
 export {
   generateImageData,
   IGatsbyImageHelperArgs,