docs: add docs for responsive images

packages/astro/src/assets/types.ts

@@ -157,26 +157,60 @@ type ImageSharedProps<T> = T & {
 	 * ```
 	 */
 	quality?: ImageQuality;
-
-	layout?: ImageLayout;
-
-	fit?: ImageFit;
-
-	position?: string;
 } & (
 		| {
 				/**
-				 * The layout type for responsive images. Overrides any default set in the Astro config.
-				 * Requires the `experimental.responsiveImages` flag to be enabled.
+				 * The layout type for responsive images. Requires the `experimental.responsiveImages` flag to be enabled in the Astro config.
+				 *
+				 * Allowed values are `responsive`, `fixed`, `full-width` or `none`. Defaults to value of `image.experimentalLayout`.
 				 *
 				 * - `responsive` - The image will scale to fit the container, maintaining its aspect ratio, but will not exceed the specified dimensions.
 				 * - `fixed` - The image will maintain its original dimensions.
-				 * - `full-width` - The image will scale to fit the container, maintaining its aspect ratio.
+				 * - `full-width` - The image will scale to fit the container, maintaining its aspect ratio, even if that means the image will exceed its original dimensions.
+				 *
+				 * **Example**:
+				 * ```astro
+				 * <Image src={...} layout="responsive" alt="..." />
+				 * ```
 				 */
+
 				layout?: ImageLayout;
-				fit?: 'fill' | 'contain' | 'cover' | 'none' | 'scale-down' | (string & {});
+
+				/**
+				 * Defines how the image should be cropped if the aspect ratio is changed. Requires the `experimental.responsiveImages` flag to be enabled in the Astro config.
+				 *
+				 * Default is `cover`. Allowed values are `fill`, `contain`, `cover`, `none` or `scale-down`. These behave like the equivalent CSS `object-fit` values. Other values may be passed if supported by the image service.
+				 *
+				 * **Example**:
+				 * ```astro
+				 * <Image src={...} fit="contain" alt="..." />
+				 * ```
+				 */
+
+				fit?: ImageFit;
+
+				/**
+				 * Defines the position of the image when cropping. Requires the `experimental.responsiveImages` flag to be enabled in the Astro config.
+				 *
+				 * The value is a string that specifies the position of the image, which matches the CSS `object-position` property. Other values may be passed if supported by the image service.
+				 *
+				 * **Example**:
+				 * ```astro
+				 * <Image src={...} position="center top" alt="..." />
+				 * ```
+				 */
+
 				position?: string;
+				/**
+				 * If true, the image will be loaded with a higher priority. This can be useful for images that are visible above the fold. There should usually be only one image with `priority` set to `true` per page.
+				 * All other images will be lazy-loaded according to when they are in the viewport.
+				 * **Example**:
+				 * ```astro
+				 * <Image src={...} priority alt="..." />
+				 * ```
+				 */
 				priority?: boolean;
+
 				/**
 				 * A list of widths to generate images for. The value of this property will be used to assign the `srcset` property on the final `img` element.
 				 *

packages/astro/src/assets/utils/imageAttributes.ts

@@ -27,7 +27,7 @@ export function applyResponsiveAttributes<
 	layout,
 	image,
 	props,
-	additionalAttributes
+	additionalAttributes,
 }: {
 	layout: Exclude<ImageLayout, 'none'>;
 	image: GetImageResult;

packages/astro/src/types/public/config.ts

@@ -1743,27 +1743,113 @@ export interface ViteUserConfig extends OriginalViteUserConfig {
 		 * @version 5.0.0
 		 * @description
 		 *
-		 * Enables and configures automatic responsive image options for images in your project. Set to `true` (for no default option passed to your images) or an object with default responsive image configuration options.
+		 * Enables automatic responsive images in your project.
 		 *
-		 * ```js
+		 * ```js title=astro.config.mjs
 		 * {
-		 *  experimental: {
-		 * 		responsiveImages: {
-		 * 			layout: 'responsive',
+		 *  	experimental: {
+		 * 			responsiveImages: true,
 		 * 		},
 		 * }
 		 * ```
 		 *
-		 * Then, you can add a `layout` option to any `<Image />` component when needed to override your default configuration: `responsive`,  `fixed`, `full-width`, or `none`. This attribute is required to transform your images if `responsiveImages.layout` is not configured.  Images with a layout value of `undefined` or `none` will not be transformed.
+		 * When enabled, you can pass a `layout` props to any `<Image />` or `<Picture />` component to create a responsive image. When a layout is set, images have automatically generated `srcset` and `sizes` attributes based on the image's dimensions and the layout type. Images with `responsive` and `full-width` layouts will have styles applied to ensure they resize according to their container.
+		 *
+		 * ```astro title=MyComponent.astro
+		 * ---
+		 * import { Image, Picture } from 'astro:assets';
+		 * import myImage from '../assets/my_image.png';
+		 * ---
+		 * <Image src={myImage} alt="A description of my image." layout='responsive' width={800} height={600} />
+		 * <Picture src={myImage} alt="A description of my image." layout='full-width' formats={['avif', 'webp', 'jpeg']} />
+		 * ```
+		 * This `<Image />` component will generate the following HTML output:
+		 * ```html title=Output
+		 *
+		 * 	<img
+		 *		src="/_astro/my_image.hash3.webp"
+		 *		srcset="/_astro/my_image.hash1.webp 640w,
+		 *						/_astro/my_image.hash2.webp 750w,
+		 *						/_astro/my_image.hash3.webp 800w,
+		 *						/_astro/my_image.hash4.webp 828w,
+		 *						/_astro/my_image.hash5.webp 1080w,
+		 *						/_astro/my_image.hash6.webp 1280w,
+		 *						/_astro/my_image.hash7.webp 1600w"
+		 *		alt="A description of my image"
+		 *		sizes="(min-width: 800px) 800px, 100vw"
+		 *		loading="lazy"
+		 *		decoding="async"
+		 *		fetchpriority="auto"
+		 *		width="800"
+		 *		height="600"
+		 *		style="--w: 800; --h: 600; --fit: cover; --pos: center;"
+		 *		data-astro-image="responsive"
+		 *  >
+		 * ```
+		 *
+		 * The following styles are applied to ensure the images resize correctly:
+		 *
+		 * ```css title="Responsive Image Styles"
+		 * [data-astro-image] {
+		 * 		width: 100%;
+		 * 		height: auto;
+		 * 		object-fit: var(--fit);
+		 * 		object-position: var(--pos);
+		 * 		aspect-ratio: var(--w) / var(--h)
+		 * }
+		 *
+		 * [data-astro-image=responsive] {
+		 * 		max-width: calc(var(--w) * 1px);
+		 * 		max-height: calc(var(--h) * 1px)
+		 * }
+		 *
+		 * [data-astro-image=fixed] {
+		 * 		width: calc(var(--w) * 1px);
+		 * 		height: calc(var(--h) * 1px)
+		 * }
+		 * ```
+		 * You can enable responsive images for all `<Image />` and `<Picture />` components by setting `image.experimentalLayout` with a default value. This can be overridden by the `layout` prop on each component.
+		 *
+		 * **Example:**
+		 * ```js title=astro.config.mjs
+		 * {
+		 * 		image: {
+		 * 			// Used for all `<Image />` and `<Picture />` components unless overridden
+		 * 			experimentalLayout: 'responsive',
+		 * 		},
+		 * 		experimental: {
+		 * 			responsiveImages: true,
+		 * 		},
+		 * }
+		 * ```
 		 *
-		 * ```astro
+		 * ```astro title=MyComponent.astro
 		 * ---
 		 * import { Image } from 'astro:assets';
 		 * import myImage from '../assets/my_image.png';
 		 * ---
-		 * <Image src={myImage} alt="A description of my image." layout='fixed' />
+		 *
+		 * <Image src={myImage} alt="This will use responsive layout" width={800} height={600} />
+		 *
+		 * <Image src={myImage} alt="This will use full-width layout" layout="full-width" />
+		 *
+		 * <Image src={myImage} alt="This will disable responsive images" layout="none" />
 		 * ```
 		 *
+		 * #### Responsive image properties
+		 *
+		 * These are additional properties available to the `<Image />` and `<Picture />` components when responsive images are enabled:
+		 *
+		 * - `layout`: The layout type for the image. Can be `responsive`, `fixed`, `full-width` or `none`. Defaults to value of `image.experimentalLayout`.
+		 * - `fit`: Defines how the image should be cropped if the aspect ratio is changed. Values match those of CSS `object-fit`. Defaults to `cover`, or the value of `image.experimentalObjectFit` if set.
+		 * - `position`: Defines the position of the image crop if the aspect ratio is changed. Values match those of CSS `object-position`. Defaults to `center`, or the value of `image.experimentalObjectPosition` if set.
+		 * - `priority`: If set, eagerly loads the image. Otherwise images will be lazy-loaded. Use this for your largest above-the-fold image. Defaults to `false`.
+		 *
+		 * The following `<Image />` component properties should not be used with responsive images as these are automatically generated:
+		 * 
+		 * - `densities`
+		 * - `widths`
+		 * - `sizes` 		 
 		 */
 
 		responsiveImages?: boolean;