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An Interactive Starry Backdrop for Content material | CSS-Methods

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I used to be lucky final 12 months to get approached by Shawn Wang (swyx) about performing some work for Temporal. The concept was to solid my artistic eye over what was on the positioning and provide you with some concepts that might give the positioning a bit “one thing” further. This was fairly a neat problem as I take into account myself extra of a developer than a designer. However I like studying and leveling up the design aspect of my sport.

One of many concepts I got here up with was this interactive starry backdrop. You’ll be able to see it working on this shared demo:

The neat factor about this design is that it’s constructed as a drop-in React element. And it’s tremendous configurable within the sense that when you’ve put collectively the foundations for it, you may make it fully your individual. Don’t need stars? Put one thing else in place. Don’t need randomly positioned particles? Place them in a constructed manner. You’ve complete management of what to bend it to your will.

So, let’s have a look at how we are able to create this drop-in element in your website! In the present day’s weapons of alternative? React, GreenSock and HTML <canvas>. The React half is completely non-compulsory, in fact, however, having this interactive backdrop as a drop-in element makes it one thing you may make use of on different initiatives.

Let’s begin by scaffolding a fundamental app

import React from 'https://cdn.skypack.dev/react'
import ReactDOM from 'https://cdn.skypack.dev/react-dom'
import gsap from 'https://cdn.skypack.dev/gsap'

const ROOT_NODE = doc.querySelector('#app')

const Starscape = () => <h1>Cool Thingzzz!</h1>

const App = () => <Starscape/>

ReactDOM.render(<App/>, ROOT_NODE)

Very first thing we have to do is render a <canvas> ingredient and seize a reference to it that we are able to use inside React’s useEffect. For these not utilizing React, retailer a reference to the <canvas> in a variable as an alternative.

const Starscape = () => {
  const canvasRef = React.useRef(null)
  return <canvas ref={canvasRef} />
}

Our <canvas> goes to wish some kinds, too. For starters, we are able to make it so the canvas takes up the complete viewport dimension and sits behind the content material:

canvas {
  place: mounted;
  inset: 0;
  background: #262626;
  z-index: -1;
  top: 100vh;
  width: 100vw;
}

Cool! However not a lot to see but.

We’d like stars in our sky

We’re going to “cheat” a bit right here. We aren’t going to attract the “traditional” pointy star form. We’re going to make use of circles of differing opacities and sizes.

Draw a circle on a <canvas> is a case of grabbing a context from the <canvas> and utilizing the arc perform. Let’s render a circle, err star, within the center. We will do that inside a React useEffect:

const Starscape = () => {
  const canvasRef = React.useRef(null)
  const contextRef = React.useRef(null)
  React.useEffect(() => {
    canvasRef.present.width = window.innerWidth
    canvasRef.present.top = window.innerHeight
    contextRef.present = canvasRef.present.getContext('second')
    contextRef.present.fillStyle="yellow"
    contextRef.present.beginPath()
    contextRef.present.arc(
      window.innerWidth / 2, // X
      window.innerHeight / 2, // Y
      100, // Radius
      0, // Begin Angle (Radians)
      Math.PI * 2 // Finish Angle (Radians)
    )
    contextRef.present.fill()
  }, [])
  return <canvas ref={canvasRef} />
}

So what now we have is a giant yellow circle:

This can be a good begin! The remainder of our code will happen inside this useEffect perform. That’s why the React half is kinda non-compulsory. You’ll be able to extract this code out and use it in whichever kind you want.

We’d like to consider how we’re going to generate a bunch of “stars” and render them. Let’s create a LOAD perform. This perform goes to deal with producing our stars in addition to the final <canvas> setup. We will additionally transfer the sizing logic of the <canvas> sizing logic into this perform:

const LOAD = () => {
  const VMIN = Math.min(window.innerHeight, window.innerWidth)
  const STAR_COUNT = Math.flooring(VMIN * densityRatio)
  canvasRef.present.width = window.innerWidth
  canvasRef.present.top = window.innerHeight
  starsRef.present = new Array(STAR_COUNT).fill().map(() => ({
    x: gsap.utils.random(0, window.innerWidth, 1),
    y: gsap.utils.random(0, window.innerHeight, 1),
    dimension: gsap.utils.random(1, sizeLimit, 1),
    scale: 1,
    alpha: gsap.utils.random(0.1, defaultAlpha, 0.1),
  }))
}

Our stars at the moment are an array of objects. And every star has properties that outline their traits, together with:

  • x: The star’s place on the x-axis
  • y: The star’s place on the y-axis
  • dimension: The star’s dimension, in pixels
  • scale: The star’s scale, which can come into play after we work together with the element
  • alpha: The star’s alpha worth, or opacity, which can even come into play throughout interactions

We will use GreenSock’s random() technique to generate a few of these values. You may additionally be questioning the place sizeLimit, defaultAlpha, and densityRatio got here from. These at the moment are props we are able to move to the Starscape element. We’ve supplied some default values for them:

const Starscape = ({ densityRatio = 0.5, sizeLimit = 5, defaultAlpha = 0.5 }) => {

A randomly generated star Object would possibly seem like this:

{
  "x": 1252,
  "y": 29,
  "dimension": 4,
  "scale": 1,
  "alpha": 0.5
}

However, we have to see these stars and we try this by rendering them. Let’s create a RENDER perform. This perform will loop over our stars and render every of them onto the <canvas> utilizing the arc perform:

const RENDER = () => {
  contextRef.present.clearRect(
    0,
    0,
    canvasRef.present.width,
    canvasRef.present.top
  )
  starsRef.present.forEach(star => {
    contextRef.present.fillStyle = `hsla(0, 100%, 100%, ${star.alpha})`
    contextRef.present.beginPath()
    contextRef.present.arc(star.x, star.y, star.dimension / 2, 0, Math.PI * 2)
    contextRef.present.fill()
  })
}

Now, we don’t want that clearRect perform for our present implementation as we’re solely rendering as soon as onto a clean <canvas>. However clearing the <canvas> earlier than rendering something isn’t a foul behavior to get into, And it’s one we’ll want as we make our canvas interactive.

Think about this demo that reveals the impact of not clearing between frames.

Our Starscape element is beginning to take form.

See the code 
const Starscape = ({ densityRatio = 0.5, sizeLimit = 5, defaultAlpha = 0.5 }) => {
  const canvasRef = React.useRef(null)
  const contextRef = React.useRef(null)
  const starsRef = React.useRef(null)
  React.useEffect(() => {
    contextRef.present = canvasRef.present.getContext('second')
    const LOAD = () => {
      const VMIN = Math.min(window.innerHeight, window.innerWidth)
      const STAR_COUNT = Math.flooring(VMIN * densityRatio)
      canvasRef.present.width = window.innerWidth
      canvasRef.present.top = window.innerHeight
      starsRef.present = new Array(STAR_COUNT).fill().map(() => ({
        x: gsap.utils.random(0, window.innerWidth, 1),
        y: gsap.utils.random(0, window.innerHeight, 1),
        dimension: gsap.utils.random(1, sizeLimit, 1),
        scale: 1,
        alpha: gsap.utils.random(0.1, defaultAlpha, 0.1),
      }))
    }
    const RENDER = () => {
      contextRef.present.clearRect(
        0,
        0,
        canvasRef.present.width,
        canvasRef.present.top
      )
      starsRef.present.forEach(star => {
        contextRef.present.fillStyle = `hsla(0, 100%, 100%, ${star.alpha})`
        contextRef.present.beginPath()
        contextRef.present.arc(star.x, star.y, star.dimension / 2, 0, Math.PI * 2)
        contextRef.present.fill()
      })
    }
    LOAD()
    RENDER()
  }, [])
  return <canvas ref={canvasRef} />
}

Have a mess around with the props on this demo to see how they have an effect on the the best way stars are rendered.

Earlier than we go additional, you’ll have seen a quirk within the demo the place resizing the viewport distorts the <canvas>. As a fast win, we are able to rerun our LOAD and RENDER capabilities on resize. Normally, we’ll wish to debounce this, too. We will add the next code into our useEffect name. Word how we additionally take away the occasion listener within the teardown.

// Naming issues is difficult...
const RUN = () => {
  LOAD()
  RENDER()
}

RUN()

// Arrange occasion dealing with
window.addEventListener('resize', RUN)
return () => {
  window.removeEventListener('resize', RUN)
}

Cool. Now after we resize the viewport, we get a brand new generated starry.

Interacting with the starry backdrop

Now for the enjoyable half! Let’s make this factor interactive.

The concept is that as we transfer our pointer across the display screen, we detect the proximity of the celebrities to the mouse cursor. Relying on that proximity, the celebrities each brighten and scale up.

We’re going to wish so as to add one other occasion listener to tug this off. Let’s name this UPDATE. It will work out the gap between the pointer and every star, then tween every star’s scale and alpha values. To ensure these tweeted values are right, we are able to use GreenSock’s mapRange() utility. In truth, inside our LOAD perform, we are able to create references to some mapping capabilities in addition to a dimension unit then share these between the capabilities if we have to.

Right here’s our new LOAD perform. Word the brand new props for scaleLimit and proximityRatio. They’re used to restrict the vary of how huge or small a star can get, plus the proximity at which to base that on.

const Starscape = ({
  densityRatio = 0.5,
  sizeLimit = 5,
  defaultAlpha = 0.5,
  scaleLimit = 2,
  proximityRatio = 0.1
}) => {
  const canvasRef = React.useRef(null)
  const contextRef = React.useRef(null)
  const starsRef = React.useRef(null)
  const vminRef = React.useRef(null)
  const scaleMapperRef = React.useRef(null)
  const alphaMapperRef = React.useRef(null)
  
  React.useEffect(() => {
    contextRef.present = canvasRef.present.getContext('second')
    const LOAD = () => {
      vminRef.present = Math.min(window.innerHeight, window.innerWidth)
      const STAR_COUNT = Math.flooring(vminRef.present * densityRatio)
      scaleMapperRef.present = gsap.utils.mapRange(
        0,
        vminRef.present * proximityRatio,
        scaleLimit,
        1
      );
      alphaMapperRef.present = gsap.utils.mapRange(
        0,
        vminRef.present * proximityRatio,
        1,
        defaultAlpha
      );
    canvasRef.present.width = window.innerWidth
    canvasRef.present.top = window.innerHeight
    starsRef.present = new Array(STAR_COUNT).fill().map(() => ({
      x: gsap.utils.random(0, window.innerWidth, 1),
      y: gsap.utils.random(0, window.innerHeight, 1),
      dimension: gsap.utils.random(1, sizeLimit, 1),
      scale: 1,
      alpha: gsap.utils.random(0.1, defaultAlpha, 0.1),
    }))
  }
}

And right here’s our UPDATE perform. It calculates the gap and generates an acceptable scale and alpha for a star:

const UPDATE = ({ x, y }) => {
  starsRef.present.forEach(STAR => {
    const DISTANCE = Math.sqrt(Math.pow(STAR.x - x, 2) + Math.pow(STAR.y - y, 2));
    gsap.to(STAR, {
      scale: scaleMapperRef.present(
        Math.min(DISTANCE, vminRef.present * proximityRatio)
      ),
      alpha: alphaMapperRef.present(
        Math.min(DISTANCE, vminRef.present * proximityRatio)
      )
    });
  })
};

However wait… it doesn’t do something?

Properly, it does. However, we haven’t set our element as much as present updates. We have to render new frames as we work together. We will attain for requestAnimationFrame typically. However, as a result of we’re utilizing GreenSock, we are able to make use of gsap.ticker. That is also known as “the heartbeat of the GSAP engine” and it’s is an efficient substitute for requestAnimationFrame.

To make use of it, we add the RENDER perform to the ticker and ensure we take away it within the teardown. One of many neat issues about utilizing the ticker is that we are able to dictate the variety of frames per second (fps). I prefer to go together with a “cinematic” 24fps:

// Take away RUN
LOAD()
gsap.ticker.add(RENDER)
gsap.ticker.fps(24)

window.addEventListener('resize', LOAD)
doc.addEventListener('pointermove', UPDATE)
return () => {
  window.removeEventListener('resize', LOAD)
  doc.removeEventListener('pointermove', UPDATE)
  gsap.ticker.take away(RENDER)
}

Word how we’re now additionally working LOAD on resize. We additionally want to ensure our scale is being picked up in that RENDER perform when utilizing arc:

const RENDER = () => {
  contextRef.present.clearRect(
    0,
    0,
    canvasRef.present.width,
    canvasRef.present.top
  )
  starsRef.present.forEach(star => {
    contextRef.present.fillStyle = `hsla(0, 100%, 100%, ${star.alpha})`
    contextRef.present.beginPath()
    contextRef.present.arc(
      star.x,
      star.y,
      (star.dimension / 2) * star.scale,
      0,
      Math.PI * 2
    )
    contextRef.present.fill()
  })
}

It really works! 🙌

It’s a really refined impact. However, that’s intentional as a result of, whereas it’s is tremendous neat, we don’t need this form of factor to distract from the precise content material. I’d suggest taking part in with the props for the element to see totally different results. It is sensible to set all the celebrities to low alpha by default too.

The next demo lets you play with the totally different props. I’ve gone for some fairly standout defaults right here for the sake of demonstration! However bear in mind, this text is extra about exhibiting you the methods so you may go off and make your individual cool backdrops — whereas being conscious of the way it interacts with content material.

Refinements

There’s one concern with our interactive starry backdrop. If the mouse cursor leaves the <canvas>, the celebrities keep vivid and upscaled however we wish them to return to their authentic state. To repair this, we are able to add an additional handler for pointerleave. When the pointer leaves, this tweens the entire stars all the way down to scale 1 and the unique alpha worth set by defaultAlpha.

const EXIT = () => {
  gsap.to(starsRef.present, {
    scale: 1,
    alpha: defaultAlpha,
  })
}

// Arrange occasion dealing with
window.addEventListener('resize', LOAD)
doc.addEventListener('pointermove', UPDATE)
doc.addEventListener('pointerleave', EXIT)
return () => {
  window.removeEventListener('resize', LOAD)
  doc.removeEventListener('pointermove', UPDATE)
  doc.removeEventListener('pointerleave', EXIT)
  gsap.ticker.take away(RENDER)
}

Neat! Now our stars cut back down and return to their earlier alpha when the mouse cursor leaves the scene.

Bonus: Including an Easter egg

Earlier than we wrap up, let’s add a bit Easter egg shock to our interactive starry backdrop. Ever heard of the Konami Code? It’s a well-known cheat code and a cool manner so as to add an Easter egg to our element.

We will virtually do something with the backdrop as soon as the code runs. Like, we may make all the celebrities pulse in a random manner for instance. Or they might come to life with further colours? It’s a possibility to get artistic with issues!

We’re going pay attention for keyboard occasions and detect whether or not the code will get entered. Let’s begin by making a variable for the code:

const KONAMI_CODE =
  'arrowup,arrowup,arrowdown,arrowdown,arrowleft,arrowright,arrowleft,arrowright,keyb,keya';

Then we create a second impact inside our the starry backdrop. This can be a good solution to keep a separation of considerations in that one impact handles all of the rendering, and the opposite handles the Easter egg. Particularly, we’re listening for keyup occasions and examine whether or not our enter matches the code.

const codeRef = React.useRef([])
React.useEffect(() => {
  const handleCode = e => {
    codeRef.present = [...codeRef.current, e.code]
      .slice(
        codeRef.present.size > 9 ? codeRef.present.size - 9 : 0
      )
    if (codeRef.present.be part of(',').toLowerCase() === KONAMI_CODE) {
      // Get together in right here!!!
    }
  }
  window.addEventListener('keyup', handleCode)
  return () => {
    window.removeEventListener('keyup', handleCode)
  }
}, [])

We retailer the person enter in an Array that we retailer inside a ref. As soon as we hit the occasion code, we are able to clear the Array and do no matter we wish. For instance, we could create a gsap.timeline that does one thing to our stars for a given period of time. If that is so, we don’t wish to enable Konami code to enter whereas the timeline is energetic. As a substitute, we are able to retailer the timeline in a ref and make one other examine earlier than working the occasion code.

const partyRef = React.useRef(null)
const isPartying = () =>
  partyRef.present &&
  partyRef.present.progress() !== 0 &&
  partyRef.present.progress() !== 1;

For this instance, I’ve created a bit timeline that colours every star and strikes it to a brand new place. This requires updating our LOAD and RENDER capabilities.

First, we’d like every star to now have its personal hue, saturation and lightness:

// Producing stars! ⭐️
starsRef.present = new Array(STAR_COUNT).fill().map(() => ({
  hue: 0,
  saturation: 0,
  lightness: 100,
  x: gsap.utils.random(0, window.innerWidth, 1),
  y: gsap.utils.random(0, window.innerHeight, 1),
  dimension: gsap.utils.random(1, sizeLimit, 1),
  scale: 1,
  alpha: defaultAlpha
}));

Second, we have to take these new values into consideration when rendering takes place:

starsRef.present.forEach((star) => {
  contextRef.present.fillStyle = `hsla(
    ${star.hue},
    ${star.saturation}%,
    ${star.lightness}%,
    ${star.alpha}
  )`;
  contextRef.present.beginPath();
  contextRef.present.arc(
    star.x,
    star.y,
    (star.dimension / 2) * star.scale,
    0,
    Math.PI * 2
  );
  contextRef.present.fill();
});

And right here’s the enjoyable little bit of code that strikes all the celebrities round:

partyRef.present = gsap.timeline().to(starsRef.present, {
  scale: 1,
  alpha: defaultAlpha
});

const STAGGER = 0.01;

for (let s = 0; s < starsRef.present.size; s++) {
  partyRef.present
    .to(
    starsRef.present[s],
    {
      onStart: () => {
        gsap.set(starsRef.present[s], {
          hue: gsap.utils.random(0, 360),
          saturation: 80,
          lightness: 60,
          alpha: 1,
        })
      },
      onComplete: () => {
        gsap.set(starsRef.present[s], {
          saturation: 0,
          lightness: 100,
          alpha: defaultAlpha,
        })
      },
      x: gsap.utils.random(0, window.innerWidth),
      y: gsap.utils.random(0, window.innerHeight),
      length: 0.3
    },
    s * STAGGER
  );
}

From there, we generate a brand new timeline and tween the values of every star. These new values get picked up by RENDER. We’re including a stagger by positioning every tween within the timeline utilizing GSAP’s place parameter.

That’s it!

That’s one solution to make an interactive starry backdrop in your website. We mixed GSAP and an HTML <canvas>, and even sprinkled in some React that makes it extra configurable and reusable. We even dropped an Easter egg in there!

The place can you’re taking this element from right here? How would possibly you apply it to a website? The mix of GreenSock and <canvas> is loads of enjoyable and I’m wanting ahead to seeing what you make! Listed here are a pair extra concepts to get your artistic juices flowing…



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