@merchantlabs/gatsby-image-loader

@merchantlabs/gatsby-image-loader

This component implements the same optimizations for images as gatsby-image except instead of rendering an image it uses the render props pattern and provides the optimized image's src as well as its loading state. The src can then be used however you want.

See the gatsby-image README for more background on the problem these optimizations solve.

Install

npm install --save @merchantlabs/gatsby-image-loader

Depending on the gatsby starter you used, you may need to include gatsby-transformer-sharp and gatsby-plugin-sharp as well, and make sure they are installed and included in your gatsby-config.

npm install --save gatsby-transformer-sharp
npm install --save gatsby-plugin-sharp

Then in your gatsby-config.js:

plugins: [
  `gatsby-transformer-sharp`,
  `gatsby-plugin-sharp`
];

How to use

This is what a component using gatsby-image-loader looks like:

import React from "react";
import ImageLoader from "@merchantlabs/gatsby-image-loader";

export default ({ data }) => (
  <div>
    <h1>Hello gatsby-image</h1>
    <ImageLoader resolutions={data.file.childImageSharp.resolutions}>
      {({ src }) => (
        <div style={{ backgroundImage: src }}> Joe ✌🏼 </div>
      )}
    </ImageLoader>
  </div>
);

export const query = graphql`
  query GatsbyImageSampleQuery {
    file(relativePath: { eq: "blog/avatars/joe-isabell.jpeg" }) {
      childImageSharp {
        # Specify the image processing specifications right in the query.
        # Makes it trivial to update as your page's design changes.
        resolutions(width: 125, height: 125) {
          ...GatsbyImageSharpResolutions
        }
      }
    }
  }
`;

Two types of responsive images

There are two types of responsive images supported by gatsby-image.

1. Images that have a fixed width and height
2. Images that stretch across a fluid container

In the first scenario, you want to vary the image's size for different screen resolutions -- in other words, create retina images.

For the second scenario, you want to create multiple sizes of thumbnails for devices with widths stretching from smartphone to wide desktop monitors.

To decide between the two, ask yourself: "do I know the exact size this image will be?" If yes, it's the first type. If no and its width and/or height need to vary depending on the size of the screen, then it's the second type.

In Gatsby's GraphQL implementation, you query for the first type by querying a child object of an image called resolutions — which you can see in the sample component above. For the second type, you do a similar query but for a child object called sizes.

Fragments

GraphQL includes a concept called "query fragments". Which, as the name suggests, are a part of a query that can be used in multiple queries. To ease building with gatsby-image, Gatsby image processing plugins which support gatsby-image ship with fragments which you can easily include in your queries.

Note, due to a limitation of GraphiQL, you can not currently use these fragments in the GraphiQL IDE.

Plugins supporting gatsby-image currently include gatsby-transformer-sharp, gatsby-source-contentful and gatsby-source-datocms.

Their fragments are:

gatsby-transformer-sharp

• GatsbyImageSharpResolutions
• GatsbyImageSharpResolutions_noBase64
• GatsbyImageSharpResolutions_tracedSVG
• GatsbyImageSharpResolutions_withWebp
• GatsbyImageSharpResolutions_withWebp_noBase64
• GatsbyImageSharpResolutions_withWebp_tracedSVG
• GatsbyImageSharpSizes
• GatsbyImageSharpSizes_noBase64
• GatsbyImageSharpSizes_tracedSVG
• GatsbyImageSharpSizes_withWebp
• GatsbyImageSharpSizes_withWebp_noBase64
• GatsbyImageSharpSizes_withWebp_tracedSVG

gatsby-source-contentful

• GatsbyContentfulResolutions
• GatsbyContentfulResolutions_noBase64
• GatsbyContentfulResolutions_withWebp
• GatsbyContentfulResolutions_withWebp_noBase64
• GatsbyContentfulSizes
• GatsbyContentfulSizes_noBase64
• GatsbyContentfulSizes_withWebp
• GatsbyContentfulSizes_withWebp_noBase64

gatsby-source-datocms

• GatsbyDatoCmsResolutions
• GatsbyDatoCmsResolutions_noBase64
• GatsbyDatoCmsSizes
• GatsbyDatoCmsSizes_noBase64

If you don't want to use the blur-up effect, choose the fragment with noBase64 at the end. If you want to use the traced placeholder SVGs, choose the fragment with tracedSVG at the end.

If you want to automatically use WebP images when the browser supports the file format, use the withWebp fragments. If the browser doesn't support WebP, gatsby-image will fall back to the default image format.

Please see the gatsby-plugin-sharp documentation for more information on tracedSVG and its configuration options.

"Resolutions" queries

Component

Pass in the data returned from the resolutions object in your query via the resolutions prop. e.g. <ImageLoader resolutions={resolutions}> {({ src }) => {...}} </ImageLoader>

Query

{
  imageSharp {
    # Other options include height (set both width and height to crop),
    # grayscale, duotone, rotate, etc.
    resolutions(width: 400) {
      # Choose either the fragment including a small base64ed image, a traced placeholder SVG, or one without.
      ...GatsbyImageSharpResolutions
    }
  }
}

"Sizes" queries

Component

Pass in the data returned from the sizes object in your query via the sizes prop. e.g. <ImageLoader sizes={sizes}> {({ src }) => {...}} </ImageLoader>

Query

{
  imageSharp {
    # i.e. the max width of your container is 700 pixels.
    #
    # Other options include maxHeight (set both maxWidth and maxHeight to crop),
    # grayscale, duotone, rotate, etc.
    sizes(maxWidth: 700) {
      # Choose either the fragment including a small base64ed image, a traced placeholder SVG, or one without.
      ...GatsbyImageSharpSizes_noBase64
    }
  }
}

gatsby-image-loader props

Name	Type	Description
resolutions	object	Data returned from the resolutions query
sizes	object	Data returned from the sizes query
title	string	Passed to the underlying hidden img element
alt	string	Passed to the underlying hidden img element
onLoad	func	A callback that is called when the full-size image has loaded.
children	func	Function that receives src and imgLoaded as props and returns a React component

Image processing arguments

gatsby-plugin-sharp supports many additional arguments for transforming your images like quality,sizeByPixelDensity,pngCompressionLevel,cropFocus,greyscale and many more. See its documentation for more.