JSFiddle - React, Tailwind, and code Playground

by Josh Pullen

CSS

canvas {
  /* border: 1px solid black; */
  max-width: calc(100vw - 20px);
  max-height: calc(100vh - 20px);
}

JavaScript

const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");

function drawGrid() {
	ctx.beginPath();
	for (let x = -3; x <= 3; x++) {
  	ctx.moveTo(x, -100);
    ctx.lineTo(x, 100);
  }
  for (let y = -3; y <= 3; y++) {
  	ctx.moveTo(-100, y);
    ctx.lineTo(100, y);
  }
  ctx.strokeStyle = "#ddd";
  ctx.lineWidth = 0.02;
  ctx.stroke();
}

function drawFunction(f) {
	ctx.beginPath();
  ctx.moveTo(-4, f(-4));
  for (let x = -4; x <= 4; x += 0.05) {
  	ctx.lineTo(x, f(x));
  }
  ctx.strokeStyle = "black";
  ctx.lineWidth = 0.05;
  ctx.stroke();
}

const getMathCoords = (canvasX, canvasY) => {
	return [
  	(canvasX - canvas.width / 2) / 100,
    -(canvasY - canvas.height / 2) / 100
  ];
}

const hslToRgb = (h, s, l) => {
    var r, g, b;

    if(s == 0){
        r = g = b = l; // achromatic
    }else{
        var hue2rgb = function hue2rgb(p, q, t){
            if(t < 0) t += 1;
            if(t > 1) t -= 1;
            if(t < 1/6) return p + (q - p) * 6 * t;
            if(t < 1/2) return q;
            if(t < 2/3) return p + (q - p) * (2/3 - t) * 6;
            return p;
        }

        var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
        var p = 2 * l - q;
        r = hue2rgb(p, q, h + 1/3);
        g = hue2rgb(p, q, h);
        b = hue2rgb(p, q, h - 1/3);
    }

    return [Math.round(r * 255), Math.round(g * 255), Math.round(b * 255)];
}

function drawHeatmap(f) {
	const imgData = ctx.createImageData(canvas.width, canvas.height);
  for (let x = 0; x < imgData.width; x++) {
    for (let y = 0; y < imgData.height; y++) {
    	const [mx, my] = getMathCoords(x, y);
      const [r = 0, g = 0, b = 0, a = 1] = f(mx, my);
      imgData.data[(x + y * imgData.width) * 4 + 0] = r * 255;
      imgData.data[(x + y * imgData.width) * 4 + 1] = g * 255;
      imgData.data[(x + y * imgData.width) * 4 + 2] = b * 255;
      imgData.data[(x + y * imgData.width) * 4 + 3] = a * 255;
    }
  }
  ctx.putImageData(imgData, 0, 0);
}

function render() {
 ...