Backmoji

This library is still under development, and the APIs are not stable yet.

With vanilla JavaScript

Install

npm install backmoji

Usage

import { backmoji, createImageRenderer } from "backmoji";
import JSLogo from "/javascript.png";

const canvas = document.createElement("canvas");
document.body.appendChild(canvas);

async function loadImage(url) {
  const image = new Image();
  image.src = url;
  return new Promise()((resolve) => {
    image.onload = () => resolve(image);
  });
}

async function createRenderer() {
  return createImageRenderer(await loadImage(JSLogo));
}

const { render } = backmoji(canvas, createRenderer(), {
  rowGap: 15,
  columnGap: 20,
  degree: 30,
});
render();

With Vue

Install

npm install @backmoji/vue

Usage

<script setup lang="ts">
import { ref, watchEffect } from "vue";
import { useBackmoji, useImageLoader, useImageRenderer } from "@backmoji/vue";
import VueLogo from "/vue.svg";

const canvasRef = ref<HTMLCanvasElement>();
const image = useImageLoader(VueLogo);
const renderer = useImageRenderer(image);
const { render } = useBackmoji(canvasRef, renderer, {
  rowGap: 15,
  columnGap: 20,
  degree: 30,
});
watchEffect(() => {
  render();
});
</script>

<template>
  <canvas ref="canvasRef"></canvas>
</template>

With React

Install

npm install @backmoji/react

Usage

import { useBackmoji, useImageLoader, useImageRenderer } from "@backmoji/react";
import { useEffect, useRef, useState } from "react";
import ReactLogo from "/react.svg";

export function WithReact() {
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const [mounted, setMounted] = useState(false);

  useEffect(() => {
    setMounted(true);
  }, []);

  const img = useImageLoader(ReactLogo);
  const renderer = useImageRenderer(img);
  const { render } = useBackmoji(canvasRef, renderer, {
    rowGap: 15,
    columnGap: 20,
    degree: 30,
  });

  useEffect(() => {
    if (mounted) {
      render();
    }
  }, [mounted, render]);

  return <canvas ref={canvasRef}></canvas>;
}

Examples

Render a text pattern

You can create a text pattern using createTextRenderer function exported by backmoji. You can adjust the font and size of the text by setting font as shown in the code below, and you can also adjust the spacing between the texts and the rotation by setting rowGap, columnGap and degree.

import { backmoji, createTextRenderer } from "backmoji";

const parent = document.querySelector<HTMLDivElement>("#demo-text-pattern")!;
const canvas = document.createElement("canvas");

const renderer = createTextRenderer("Hello World!", {
  font: "30px Aria",
});
const height = 160;
const { render, setSize } = backmoji(canvas, renderer, {
  degree: -45,
  rowGap: 50,
  columnGap: 40,
});

setSize(parent.clientWidth, height);

const observer = new ResizeObserver((entries) => {
  for (const entry of entries) {
    setSize(entry.contentRect.width, height);
    render();
  }
});
observer.observe(parent);

parent.appendChild(canvas);
render();

Also, you can render an emoji for emoji is a type of text.

Render an image pattern

Rendering an image is similar to rendering text. You can create an image pattern using createImageRenderer. createImageRenderer accepts an image element. Make sure the image has loaded before the first render.

import { backmoji, createImageRenderer } from "backmoji";
import JSLogo from "/javascript.png";

const canvas = document.createElement("canvas");
const parent = document.querySelector<HTMLDivElement>("#demo-image-pattern")!;

function loadImage(url: string) {
  const image = new Image();
  image.src = url;
  return new Promise<HTMLImageElement>((resolve) => {
    image.onload = () => resolve(image);
  });
}

async function createRenderer() {
  return createImageRenderer(await loadImage(JSLogo));
}

const height = 300;
const { render, setSize } = backmoji(canvas, createRenderer(), {
  degree: -30,
  rowGap: 50,
  columnGap: 60,
});

const observer = new ResizeObserver((entries) => {
  for (const entry of entries) {
    setSize(entry.contentRect.width, height);
    render();
  }
});
observer.observe(parent);

parent.appendChild(canvas);
render();

With custom render function

Sometimes you may need to render patterns with special arrangements, such as a chessboard-like staggered arrangement. You can use the second parameter options.customRender provided by createTextRenderer or createImageRenderer to handle the rendering position yourself.

import { backmoji, createImageRenderer } from "backmoji";
import JSLogo from "/javascript.png";

const canvas = document.createElement("canvas");
const parent = document.querySelector<HTMLDivElement>("#demo-custom-pattern")!;

function loadImage(url: string) {
  const image = new Image();
  image.src = url;
  return new Promise<HTMLImageElement>((resolve) => {
    image.onload = () => resolve(image);
  });
}

async function createRenderer() {
  return createImageRenderer(await loadImage(JSLogo), {
    customRender({ ctx, item, renderItemWidth, renderItemHeight, rowGap, columnGap, columnCount, rowCount }) {
      for (let rowIndex = 0; rowIndex < rowCount; rowIndex++) {
        let from: number, to: number;
        if (rowIndex % 2 === 0) {
          from = -2;
          to = columnCount;
        } else {
          from = 0;
          to = columnCount + 2;
        }
        for (let columnIndex = from; columnIndex < to; columnIndex++) {
          const x = columnIndex * (renderItemWidth + columnGap);
          const y = rowIndex * (renderItemHeight + rowGap);
          if ((columnIndex - rowIndex) % 2 === 0) {
            ctx.drawImage(item, x, y, renderItemWidth, renderItemHeight);
          }
        }
      }
    },
  });
}

const height = 300;
const { render, setSize } = backmoji(canvas, createRenderer());

const observer = new ResizeObserver((entries) => {
  for (const entry of entries) {
    setSize(entry.contentRect.width, height);
    render();
  }
});
observer.observe(parent);

parent.appendChild(canvas);
render();

With animation

backmoji itself does not provide any animation-related functionality, but through customRender, you can implement your own animation functionality, just like the animated background on this website. Here is a demonstration related to animation functionality.

// animation.ts
import { isDefined } from "@bernankez/utils";
import Stats from "stats.js";

export type Fn = () => void;

export function animate(options?: {
  speed?: number;
}) {
  let { speed: _speed = 0.5 } = options || {};

  let _callback: Fn | undefined;
  let _isPlay = false;
  let _timestamp = 0;
  let _ref: number | undefined;

  const _stats = new Stats();
  _stats.showPanel(0);

  function getTimestamp() {
    return _timestamp;
  }

  function setSpeed(speed: number) {
    _speed = speed;
  }

  function setCallback(callback: Fn) {
    _callback = callback;
  }

  function toggle(play?: boolean) {
    const isPlay = isDefined(play) ? play : !_isPlay;
    if (isPlay === _isPlay) {
      return;
    }
    if (isPlay) {
      _play();
    } else {
      _pause();
    }
    _isPlay = isPlay;
  }

  function _play() {
    if (!_callback) {
      return;
    }
    _timestamp += _speed;
    _stats.begin();
    _callback();
    _stats.end();
    _ref = requestAnimationFrame(_play);
  }

  function _pause() {
    if (_ref) {
      cancelAnimationFrame(_ref);
      _ref = undefined;
    }
  }

  function _reset() {
    _timestamp = 0;
    _pause();
    _callback?.();
  }

  return {
    stat: _stats,

    getTimestamp,

    setSpeed,
    setCallback,

    toggle,
    play: _play,
    pause: _pause,
    reset: _reset,
  };
}

import { backmoji, createImageRenderer } from "backmoji";
import { animate } from "@/utils/animation";
import Paw from "/paw.svg";

const { play, setCallback, getTimestamp, stat } = animate({
  speed: 0.3,
});

const canvas = document.createElement("canvas");
const parent = document.querySelector<HTMLDivElement>("#demo-animation-pattern")!;

function loadImage(url: string) {
  const image = new Image();
  image.src = url;
  return new Promise<HTMLImageElement>((resolve) => {
    image.onload = () => resolve(image);
  });
}

async function createRenderer() {
  return createImageRenderer(await loadImage(Paw), {
    customRender({ ctx, item, renderItemWidth, renderItemHeight, rowGap, columnGap, columnCount, rowCount }) {
      for (let rowIndex = 0; rowIndex < rowCount; rowIndex++) {
        let from: number, to: number;
        if (rowIndex % 2 === 0) {
          from = -2;
          to = columnCount;
        } else {
          from = 0;
          to = columnCount + 2;
        }
        for (let columnIndex = from; columnIndex < to; columnIndex++) {
          let offset = getTimestamp();
          offset = offset % (2 * (renderItemWidth + columnGap));
          const x = columnIndex * (renderItemWidth + columnGap) + (rowIndex % 2 === 0 ? 1 : -1) * offset;
          const y = rowIndex * (renderItemHeight + rowGap);
          if ((columnIndex - rowIndex) % 2 === 0) {
            ctx.drawImage(item, x, y, renderItemWidth, renderItemHeight);
          }
        }
      }
    },
  });
}

const height = 300;
const { render, setSize } = backmoji(canvas, createRenderer(), {
  degree: 30,
});

function animationCb() {
  const ctx = canvas.getContext("2d")!;
  const w = canvas.width;
  const h = canvas.height;
  ctx.clearRect(0, 0, w, h);
  render();
}

setCallback(animationCb);

const observer = new ResizeObserver((entries) => {
  for (const entry of entries) {
    setSize(entry.contentRect.width, height);
    render();
  }
});
observer.observe(parent);

parent.appendChild(canvas);
const statDom = stat.dom;
statDom.style.position = "absolute";
statDom.style.top = "0";
statDom.style.right = "0";
statDom.style.left = "unset";
parent.appendChild(statDom);

play();

Customize

You can create your own renderer if the provided renderers do not meet your needs. See renderer.ts for more details.

Options

backmoji

declare function backmoji(canvas: Awaitable<HTMLCanvasElement>, renderer: Awaitable<Renderer>, options?: BackmojiOptions): {
  render: () => Promise<void>;
  setOptions: (options: BackmojiOptions, combine?: boolean) => void;
  /*
  * Set the size of the canvas. It handles device pixel ratio automatically.
  */
  setSize: (width: number | undefined, height: number | undefined) => Promise<void>;
};

interface BackmojiOptions {
  degree?: number;
  rowGap?: number;
  columnGap?: number;
}

type Renderer = (context: RendererContext) => void;

interface RendererContext {
  ctx: CanvasRenderingContext2D;
  width: number;
  height: number;
  rowGap: number;
  columnGap: number;
  degree: number;
  angle: number;
  /*
  * Measure size of texts, using CanvasRenderingContext2D.measureText underhood
  */
  measureText: (text: string) => {
    width: number;
    fontHeight: number;
    height: number;
  };
  /*
  * Calculate how many items should be rendered each row
  */
  calculateRenderCount: (renderItemWidth: number, renderItemHeight: number) => number[] & {
    row: number;
    column: number;
  };
  /*
  * Calculate the translate after rotation
  */
  calculateTranslate: () => number[] & {
    x: number;
    y: number;
  };
}

renderer

interface CreateTextRendererOptions {
  font?: string;
  customRender?: (context: RenderContext<string>) => void;
}
/*
* The default render function if no customRender provided
*/
declare function textRender(context: RenderContext<string>): void;
declare function createTextRenderer(text: string, options?: CreateTextRendererOptions): Renderer;
interface CreateImageRendererOptions {
  customRender?: (context: RenderContext<HTMLImageElement>) => void;
}

/*
* The default render function if no customRender provided
*/
declare function imageRender(context: RenderContext<HTMLImageElement>): void;
declare function createImageRenderer(img: HTMLImageElement, options?: CreateImageRendererOptions): Renderer;

The following image explains the meanings of various attribute values: