Night Sky

A dynamic night sky background with twinkling stars, customizable density, and content layered on top.

Stars Above You

import NightSkyBackground from "@/components/backgrounds/night-sky-background/night-sky-background";

const NightSkyBackgroundPreview = () => {
  return (
    <NightSkyBackground
      style={{
        width: "100%",
        height: "100%"
      }}
      wrapperProps={{
        style: {
          height: "100%",
          display: "grid",
          placeItems: "center",
          color: "#fff",
        }
      }}
    >
      <h1>Stars Above You</h1>
    </NightSkyBackground>
  );
};

export default NightSkyBackgroundPreview;

Installation

Run the command from your project root directory (the folder that contains package.json).

npx mosaicui-cli@latest backgrounds/night-sky-background

1. Copy the component file

Create a new file called night-sky-background.jsx in your reusable components folder (for example /src/components/) and paste the following code into it.

import { useState, useRef, useEffect, useLayoutEffect, useMemo, useCallback } from "react";
import styles from "./night-sky-background.module.css";

const random = (n = 1) => {
  return Math.random() * n;
};

const NightSkyBackground = (props) => {
  const {
    density = 1,
    children,
    className,
    wrapperProps = {},
    wrapperTagName = "div",
    ...rest
  } = props;

  const {
    className: wrapperClassName = "",
    ...restWrapperProps
  } = wrapperProps;

  const Wrapper = wrapperTagName || "div";

  const spaceColor = "rgb(0, 0, 0)";

  const starsCount = useMemo(() => (
    Math.min(Math.max(100, 1000 * density), 10000)
  ), [density]);

  const containerRef = useRef();
  const canvasRef = useRef(null);
  const rafId = useRef(null);

  const [mounted, setMounted] = useState(false);
  const [width, setWidth] = useState(0);
  const [height, setHeight] = useState(0);

  const { devicePixelRatio, canvasWidth, canvasHeight } = useMemo(() => {
    const devicePixelRatio = Math.max(1, globalThis.devicePixelRatio || 1);
    return {
      devicePixelRatio,
      canvasWidth: width * devicePixelRatio,
      canvasHeight: height * devicePixelRatio,
    };
  }, [width, height]);

  const ctx = useMemo(() => {
    return canvasRef.current?.getContext("2d");
  }, [canvasRef.current]);

  const stars = useMemo(() => {
    return Array.from({ 
      length: starsCount,
    }).map(() => ({
      x: random(width),
      y: random(height),
      radius: random(),
      color: (
        random() < 0.8 ? [255, 255, 255] :  (
          [
            Math.floor(random(255)),
            Math.floor(random(255)),
            Math.floor(random(255)),
          ]
        )
      ),
      twinkingRate: random() * 0.01,
      opacity: random(),
      shouldTwinkle: random() < 0.5,
    }))
  }, [starsCount, width, height]);

  const render = useCallback(() => {
    ctx.setTransform(devicePixelRatio, 0, 0, devicePixelRatio, 0, 0);
    ctx.fillStyle = spaceColor;
    ctx.fillRect(0, 0, canvasWidth, canvasHeight);
    ctx.save();
    for (const star of stars) {
      let starOpacity = star.opacity;
      if (star.shouldTwinkle) {
        star.opacity = (star.opacity + star.twinkingRate) % 100;
        starOpacity = Math.cos(star.opacity);
      }
      ctx.beginPath();
      ctx.ellipse(
        star.x, 
        star.y, 
        star.radius, 
        star.radius, 
        0, 
        0, 
        360, 
        false
      );
      ctx.closePath();
      ctx.fillStyle = `rgba(${[...star.color, starOpacity].join(", ")})`;
      ctx.fill();
    }
    ctx.restore();
    rafId.current = requestAnimationFrame(render);
  }, [
    ctx,
    devicePixelRatio,
    width,
    height,
    canvasWidth,
    canvasHeight,
    stars,
  ]);

  useEffect(() => {
    const updateContainerDimensions = () => {
      const {
        width, 
        height,
      } = containerRef.current.getBoundingClientRect();
      setWidth(width);
      setHeight(height);
    };
    const resizeObserver = new ResizeObserver(updateContainerDimensions);
    resizeObserver.observe(containerRef.current);
    updateContainerDimensions();
    setMounted(true);
    return () => {
      resizeObserver.disconnect();
    }
  }, []);

  useLayoutEffect(() => {
    if (!mounted) return;
    render();
    return () => {
      cancelAnimationFrame(rafId.current);
    };
  }, [mounted, render]);

  return (
    <div
      {...rest}
      ref={containerRef}
      className={[
        className,
        styles["night-sky-background"]
      ].join(" ")}
    >
      <canvas
        aria-hidden={true}
        width={canvasWidth}
        height={canvasHeight}
        ref={canvasRef}
      />
      <Wrapper
        {...restWrapperProps}
        className={[
          wrapperClassName,
          styles["wrapper"]
        ].join(" ")}
      >
        {children}
      </Wrapper>
    </div>
  );
};

export default NightSkyBackground;

2. Copy the CSS module file

In the same folder, create a file called night-sky-background.module.css and paste the following CSS.

.night-sky-background {
  position: relative;
  background: rgb(0, 0, 0);

  canvas {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    width: 100%;
    height: 100%;
    z-index: 1;
  }

  .wrapper {
    position: relative;
    z-index: 3;
  }
}

Props

Configure the component with the following props:

Prop	Type	Required	Default	Description
density	`number`	No	`1`	Controls the number of stars rendered in the background. Min: 0.1, Max: 10. Higher = denser sky.
children	`ReactNode`	Yes	—	Content displayed on top of the night sky background.
className	`string`	No	—	Additional CSS classes applied to the main container.
wrapperProps	`React.HTMLAttributes<any>`	No	—	Extra props passed to the wrapper element containing the children.
wrapperTagName	`string`	No	`"div"`	HTML tag used as the wrapper element around the children.