tenMinutePhysics/21-fire.html

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<!DOCTYPE html>
<html>
	<meta name="viewport" content="width=device-width, initial-scale=1.0">

	<head>
		<title>Fire Simulation</title>
		<style>
			body {
				font-family: verdana; 
				font-size: 15px;
			}			
			.button {
				background-color: #606060;
				border: none;
				color: white;
				padding: 10px 10px;
				font-size: 16px;
				margin: 4px 2px;
				cursor: pointer;
			}
			.slider {
				-webkit-appearance: none;
				width: 80px;
				height: 6px;
				border-radius: 5px;
				background: #d3d3d3;
				outline: none;
				opacity: 0.7;
				-webkit-transition: .2s;
				transition: opacity .2s;
			}
		</style>
	</head>
	
<body onresize="onResize()">

	<input type = "checkbox" id = "burningFloor" onclick = "scene.burningFloor = !scene.burningFloor"> Floor
	<input type = "checkbox" id = "burningObstacle" onclick = "scene.burningObstacle = !scene.burningObstacle" checked> Ring
	<input type = "checkbox" id = "swirlButton" onclick = "scene.showSwirls = !scene.showSwirls"> Swirls
	<input type = "range" min = "0" max = "100" value = "50" id = "probabilitySlider" class = "slider"> Probability

	<br>
	<canvas id="myCanvas" style="border:2px solid"></canvas>
	
<script>

var scene = 
	{
		gravity : 0.00,
		dt : 1.0 / 60.0,
		numIters : 10,
		frameNr : 0,
		obstacleX : 0.0,
		obstacleY : 0.0,
		obstacleRadius: 0.2,
		burningObstacle: true,
		burningFloor: false,
		paused: false,
		showObstacle: false,
		showSwirls: false,
		swirlProbability: 50.0,
		swirlMaxRadius: 0.05,
		fluid: null
	};


	var canvas = document.getElementById("myCanvas");
	var c = canvas.getContext("2d");	
	canvas.width = window.innerWidth;
	canvas.height = window.innerHeight - 100;

	canvas.focus();

	var cScale = 1.0;

	var U_FIELD = 0;
	var V_FIELD = 1;
	var T_FIELD = 2;

	var cnt = 0;

	function cX(x) {
		return x * cScale;
	}

	function cY(y) {
		return canvas.height - y * cScale;
	}

	function kernel(r, rmax, leftBorder, rightBorder) {
		if (r >= rmax || r <= 0.0)
			return 0.0;
		else if (r < leftBorder)
			return r / leftBorder;
		else if (r <= rmax - rightBorder)
			return 1.0;
		else 
			return (rmax - r) / rightBorder;
	}


	// ----------------- start of simulator ------------------------------

	class Fluid {
		constructor(numX, numY, h) {
			this.numX = numX + 2; 
			this.numY = numY + 2;
			this.numCells = this.numX * this.numY;
			this.h = h;
			this.u = new Float32Array(this.numCells);
			this.v = new Float32Array(this.numCells);
			this.newU = new Float32Array(this.numCells);
			this.newV = new Float32Array(this.numCells);
			this.s = new Float32Array(this.numCells);
			this.t = new Float32Array(this.numCells);
			this.newT = new Float32Array(this.numCells);
			var num = numX * numY;
			this.t.fill(0.0);
			this.s.fill(1.0);
			
			this.numSwirls = 0;

			let maxSwirls = 100;
			this.swirlGlobalTime = 0.0;
			this.swirlX = new Float32Array(maxSwirls);
			this.swirlY = new Float32Array(maxSwirls);
			this.swirlOmega = new Float32Array(maxSwirls);
			this.swirlRadius = new Float32Array(maxSwirls);
			this.swirlTime = new Float32Array(maxSwirls);
			this.swirlTime.fill(0.0);
		}

		integrate(dt, gravity) {
			var n = this.numY;
			for (var i = 1; i < this.numX; i++) {
				for (var j = 1; j < this.numY-1; j++) {
					if (this.s[i*n + j] != 0.0 && this.s[i*n + j-1] != 0.0)
						this.v[i*n + j] += gravity * dt;
				}	 
			}
		}

		solveIncompressibility(numIters, dt) {

			var n = this.numY;
			let overRelaxation = 1.9;

			for (var iter = 0; iter < numIters; iter++) {

				for (var i = 1; i < this.numX-1; i++) {
					for (var j = 1; j < this.numY-1; j++) {

						if (this.s[i*n + j] == 0.0)
							continue;

						var s = this.s[i*n + j];
						var sx0 = this.s[(i-1)*n + j];
						var sx1 = this.s[(i+1)*n + j];
						var sy0 = this.s[i*n + j-1];
						var sy1 = this.s[i*n + j+1];
						var s = sx0 + sx1 + sy0 + sy1;
						if (s == 0.0)
							continue;

						var div = this.u[(i+1)*n + j] - this.u[i*n + j] + 
							this.v[i*n + j+1] - this.v[i*n + j];

						var p = -div / s;
						p *= overRelaxation;
						this.u[i*n + j] -= sx0 * p;
						this.u[(i+1)*n + j] += sx1 * p;
						this.v[i*n + j] -= sy0 * p;
						this.v[i*n + j+1] += sy1 * p;
					}
				}
			}
		}

		extrapolate() {
			var n = this.numY;
			for (var i = 0; i < this.numX; i++) {
				this.u[i*n + 0] = this.u[i*n + 1];
				this.u[i*n + this.numY-1] = this.u[i*n + this.numY-2]; 
			}
			for (var j = 0; j < this.numY; j++) {
				this.v[0*n + j] = this.v[1*n + j];
				this.v[(this.numX-1)*n + j] = this.v[(this.numX-2)*n + j] 
			}
		}

		sampleField(x, y, field) {
			var n = this.numY;
			var h = this.h;
			var h1 = 1.0 / h;
			var h2 = 0.5 * h;

			x = Math.max(Math.min(x, this.numX * h), h);
			y = Math.max(Math.min(y, this.numY * h), h);

			var dx = 0.0;
			var dy = 0.0;

			var f;

			switch (field) {
				case U_FIELD: f = this.u; dy = h2; break;
				case V_FIELD: f = this.v; dx = h2; break;
				case T_FIELD: f = this.t; dx = h2; dy = h2; break

			}

			var x0 = Math.min(Math.floor((x-dx)*h1), this.numX-1);
			var tx = ((x-dx) - x0*h) * h1;
			var x1 = Math.min(x0 + 1, this.numX-1);
			
			var y0 = Math.min(Math.floor((y-dy)*h1), this.numY-1);
			var ty = ((y-dy) - y0*h) * h1;
			var y1 = Math.min(y0 + 1, this.numY-1);

			var sx = 1.0 - tx;
			var sy = 1.0 - ty;

			var val = sx*sy * f[x0*n + y0] +
				tx*sy * f[x1*n + y0] +
				tx*ty * f[x1*n + y1] +
				sx*ty * f[x0*n + y1];
			
			return val;
		}

		avgU(i, j) {
			var n = this.numY;
			var u = (this.u[i*n + j-1] + this.u[i*n + j] +
				this.u[(i+1)*n + j-1] + this.u[(i+1)*n + j]) * 0.25;
			return u;
				
		}

		avgV(i, j) {
			var n = this.numY;
			var v = (this.v[(i-1)*n + j] + this.v[i*n + j] +
				this.v[(i-1)*n + j+1] + this.v[i*n + j+1]) * 0.25;
			return v;
		}

		advectVel(dt) {

			this.newU.set(this.u);
			this.newV.set(this.v);

			var n = this.numY;
			var h = this.h;
			var h2 = 0.5 * h;

			for (var i = 1; i < this.numX; i++) {
				for (var j = 1; j < this.numY; j++) {

					cnt++;

					// u component
					if (this.s[i*n + j] != 0.0 && this.s[(i-1)*n + j] != 0.0 && j < this.numY - 1) {
						var x = i*h;
						var y = j*h + h2;
						var u = this.u[i*n + j];
						var v = this.avgV(i, j);
						x = x - dt*u;
						y = y - dt*v;
						u = this.sampleField(x,y, U_FIELD);
						this.newU[i*n + j] = u;
					}
					// v component
					if (this.s[i*n + j] != 0.0 && this.s[i*n + j-1] != 0.0 && i < this.numX - 1) {
						var x = i*h + h2;
						var y = j*h;
						var u = this.avgU(i, j);
						var v = this.v[i*n + j];
						x = x - dt*u;
						y = y - dt*v;
						v = this.sampleField(x,y, V_FIELD);
						this.newV[i*n + j] = v;
					}
				}	 
			}

			this.u.set(this.newU);
			this.v.set(this.newV);
		}

		advectTemperature(dt) {

			this.newT.set(this.t);

			var n = this.numY;
			var h = this.h;
			var h2 = 0.5 * h;

			for (var i = 1; i < this.numX-1; i++) {
				for (var j = 1; j < this.numY-1; j++) {

					if (this.s[i*n + j] != 0.0) {
						var u = (this.u[i*n + j] + this.u[(i+1)*n + j]) * 0.5;
						var v = (this.v[i*n + j] + this.v[i*n + j+1]) * 0.5;
						var x = i*h + h2 - dt*u;
						var y = j*h + h2 - dt*v;

						this.newT[i*n + j] = this.sampleField(x,y, T_FIELD);
 					}
				}	 
			}
			this.t.set(this.newT);
		}

		updateFire(dt) {

			let h = this.h;

			let swirlTimeSpan = 1.0;
			let swirlOmega = 20.0;
			let swirlDamping = 10.0 * dt;
			let swirlProbability = scene.swirlProbability * h * h;

			var fireCooling = 1.2 * dt;
			var smokeCooling = 0.3 * dt;
			var lift = 3.0;
			var acceleration = 6.0 * dt;
			let kernelRadius = scene.swirlMaxRadius;

			// update swirls

			var n = this.numY;
			let maxX = (this.numX - 1) * this.h;
			let maxY = (this.numY - 1) * this.h;

			// kill swirls

			let num = 0
			for (let nr = 0; nr < this.numSwirls; nr++) {
				this.swirlTime[nr] -= dt;
				if (this.swirlTime[nr] > 0.0) {
					this.swirlTime[num] = this.swirlTime[nr];
					this.swirlX[num] = this.swirlX[nr];
					this.swirlY[num] = this.swirlY[nr];
					this.swirlOmega[num] = this.swirlOmega[nr];
					num++;
				}
			}
			this.numSwirls = num;

			// advect and modify velocity field

			for (let nr = 0; nr < this.numSwirls; nr++) {

				let ageScale = this.swirlTime[nr] / swirlTimeSpan;
				let x = this.swirlX[nr];
				let y = this.swirlY[nr];
				let swirlU = (1.0 - swirlDamping) * this.sampleField(x, y, U_FIELD);
				let swirlV = (1.0 - swirlDamping) * this.sampleField(x, y, V_FIELD);
				x += swirlU * dt;
				y += swirlV * dt;
				x = Math.min(Math.max(x, h), maxX);
				y = Math.min(Math.max(y, h), maxY);

				this.swirlX[nr] = x;
				this.swirlY[nr] = y;
				let omega = this.swirlOmega[nr];

				// update surrounding velocity field

				let x0 = Math.max(Math.floor((x - kernelRadius) / h), 0);
				let y0 = Math.max(Math.floor((y - kernelRadius) / h), 0);
				let x1 = Math.min(Math.floor((x + kernelRadius) / h) + 1, this.numX - 1);
				let y1 = Math.min(Math.floor((y + kernelRadius) / h) + 1, this.numY - 1);

				for (let i = x0; i <= x1; i++) {
					for (let j = y0; j <= y1; j++) {
						for (let dim = 0; dim < 2; dim++) {

							let vx = dim == 0 ? i * h : (i + 0.5) * h;
							let vy = dim == 0 ? (j + 0.5) * h : j * h;

							let rx = vx - x;
							let ry = vy - y;
							let r = Math.sqrt(rx * rx + ry * ry);

							if (r < kernelRadius) {
								let s = 1.0;
								if (r > 0.8 * kernelRadius) {
									s = 5.0 - 5.0 / kernelRadius * r;
									// s = (kernelRadius - r) / kernelRadius * ageScale;
								}
							
								if (dim == 0) {
									let target = ry * omega + swirlU;
									let u = this.u[n*i + j];
									this.u[n*i + j] = (target - u) * s;
								}
								else {
									let target = -rx * omega + swirlV;
									let v = this.v[n*i + j];
									this.v[n*i + j] += (target - v) * s;
								}
							}
						}
					}
				}
			}

			// update temperatures 

			let minR = 0.85 * scene.obstacleRadius;
			let maxR = scene.obstacleRadius + h;

			for (var i = 0; i < this.numX; i++) {
				for (var j = 0; j < this.numY; j++) {
					let t = this.t[i*n + j];

					let cooling = t < 0.3 ? smokeCooling : fireCooling;
					this.t[i*n + j] = Math.max(t - cooling, 0.0);
					let u = this.u[i*n + j];
					let v = this.v[i*n + j];
					let targetV = t * lift;
					this.v[i*n + j] += (targetV - v) * acceleration;

					let numNewSwirls = 0;

					// obstacle burning
					if (scene.burningObstacle) {
						let dx = (i + 0.5) * this.h - scene.obstacleX;
						let dy = (j + 0.5) * this.h - scene.obstacleY - 3.0 * this.h;
						let d = dx * dx + dy * dy;
						if (minR * minR <= d && d < maxR * maxR) {
							this.t[i*n + j] = 1.0;
							if (Math.random() < 0.5 * swirlProbability)
								numNewSwirls++;
						}
					}

					// floor burning
					if (j < 4 && scene.burningFloor) {
						this.t[i*n + j] = 1.0;
						this.u[i*n + j] = 0.0;
						this.v[i*n + j] = 0.0;
						if (Math.random() < swirlProbability)
							numNewSwirls++;
					}

					for (let k = 0; k < numNewSwirls; k++) {
						if (this.numSwirls >= this.maxSwirls)
							break;
						let nr = this.numSwirls;
						this.swirlX[nr] = i * h;
						this.swirlY[nr] = j * h;
						this.swirlOmega[nr] = (-1.0 + 2.0 * Math.random()) * swirlOmega;
						this.swirlTime[nr] = swirlTimeSpan;
						this.numSwirls++;
					}
				}
			}

			// foo: maybe for obstacle
			
			// smooth temperatures

			for (let i = 1; i < this.numX - 1; i++) {
				for (let j = 1; j < this.numY - 1; j++) {
					let t = this.t[i * n + j];
					if (t == 1.0) {
						let avg = (
							this.t[(i - 1) * n + (j - 1)] + 
							this.t[(i + 1) * n + (j - 1)] + 
							this.t[(i + 1) * n + (j + 1)] + 
							this.t[(i - 1) * n + (j + 1)]) * 0.25;
						this.t[i * n + j] = avg;
					}
				}
			}
		}

		// ----------------- end of simulator ------------------------------

		simulate(dt, gravity, numIters) {

			this.integrate(dt, gravity);

			this.solveIncompressibility(numIters, dt);
			this.extrapolate();
			this.advectVel(dt);
			this.advectTemperature(dt);
			this.updateFire(dt);
		}
	}

	function setupScene() 
	{
		var canvas = document.getElementById("myCanvas");
		canvas.width = window.innerWidth;
		canvas.height = window.innerHeight - 20;

		let simHeight = 1.0;	
		cScale = canvas.height / simHeight;
		let simWidth = canvas.width / cScale;

		var numCells = 100000;
		var h = Math.sqrt(simWidth * simHeight / numCells);

		var numX = Math.floor(simWidth / h);
		var numY = Math.floor(simHeight / h);

		if (numX < numY) {
			scene.swirlProbability = 80.0;
			scene.swirlMaxRadius = 0.04;
		}

		scene.obstacleX = 0.5 * numX * h;
		scene.obstacleY = 0.3 * numY * h;
		scene.showObstacle = scene.burningObstacle;

		scene.fluid = new Fluid(numX, numY, h);
	}


	// draw -------------------------------------------------------

	function setColor(r,g,b) {
		c.fillStyle = `rgb(
			${Math.floor(255*r)},
			${Math.floor(255*g)},
			${Math.floor(255*b)})`
		c.strokeStyle = `rgb(
			${Math.floor(255*r)},
			${Math.floor(255*g)},
			${Math.floor(255*b)})`
	}

	function getFireColor(val) {
		val = Math.min(Math.max(val, 0.0), 1.0);
		var r, g, b;

		if (val < 0.3) {
			let s = val / 0.3;
			r = 0.2 * s; g = 0.2 * s; b = 0.2 * s; 
		}
		else if (val < 0.5) {
			let s = (val-0.3) / 0.2;
			r = 0.2 + 0.8 * s; g = 0.1; b = 0.1;
		}
		else  {
			let s = (val - 0.5) / 0.48;
			r = 1.0; g = s; b = 0.0;
		}
		return[255*r,255*g,255*b, 255]
	}

	function draw() 
	{
		c.clearRect(0, 0, canvas.width, canvas.height);

		c.fillStyle = "#FF0000";
		f = scene.fluid;
		n = f.numY;

		var cellScale = 1.1;

		var h = f.h;

		id = c.getImageData(0,0, canvas.width, canvas.height)

		var color = [255, 255, 255, 255]

		for (var i = 0; i < f.numX; i++) {
			for (var j = 0; j < f.numY; j++) {

				var t = f.t[i*n + j];
				color = getFireColor(t, 0.0, 1.0);

				var x = Math.floor(cX(i * h));
				var y = Math.floor(cY((j+1) * h));
				var cx = Math.floor(cScale * cellScale * h) + 1;
				var cy = Math.floor(cScale * cellScale * h) + 1;

				r = color[0];
				g = color[1];
				b = color[2];

				for (var yi = y; yi < y + cy; yi++) {
					var p = 4 * (yi * canvas.width + x)

					for (var xi = 0; xi < cx; xi++) {
						id.data[p++] = r;
						id.data[p++] = g;
						id.data[p++] = b;
						id.data[p++] = 255;
					}
				}
			}
		}

		c.putImageData(id, 0, 0);

		if (scene.showObstacle) {

			r = scene.obstacleRadius + f.h;
			if (scene.showPressure)
				c.fillStyle = "#000000";
			else
				c.fillStyle = "#DDDDDD";
			// c.beginPath();	
			// c.arc(
			// 	cX(scene.obstacleX), cY(scene.obstacleY), cScale * r, 0.0, 2.0 * Math.PI); 
			// c.closePath();
			// c.fill();

			c.lineWidth = 20.0;
			c.strokeStyle = "#404040";
			c.beginPath();	
			c.arc(
				cX(scene.obstacleX), cY(scene.obstacleY), cScale * r, 0.0, 2.0 * Math.PI); 
			c.closePath();
			c.stroke();
			c.lineWidth = 1.0;
		}

		if (scene.showSwirls) {

			for (let i = 0; i < f.numSwirls; i++) {
				let x = f.swirlX[i];
				let y = f.swirlY[i];
				let r = scene.swirlMaxRadius;

				c.lineWidth = 1.0;
				c.strokeStyle = "#303030";
				c.beginPath();	
				c.arc(
					cX(x), cY(y), cScale * r, 0.0, 2.0 * Math.PI); 
				c.closePath();
				c.stroke();
				c.lineWidth = 1.0;
			}
		}
	}

	function setObstacle(x, y, reset) {

		var vx = 0.0;
		var vy = 0.0;

		if (!reset) {
			vx = (x - scene.obstacleX) / scene.dt;
			vy = (y - scene.obstacleY) / scene.dt;
		}

		scene.obstacleX = x;
		scene.obstacleY = y;
		scene.showObstacle = true;

		var r = scene.obstacleRadius;
		var f = scene.fluid;
		var n = f.numY;
		var cd = Math.sqrt(2) * f.h;

		for (var i = 1; i < f.numX-2; i++) {
			for (var j = 1; j < f.numY-2; j++) {

				f.s[i*n + j] = 1.0;

				dx = (i + 0.5) * f.h - x;
				dy = (j + 0.5) * f.h - y;

				let d2 = dx * dx + dy * dy;
				if (d2 < r * r) {
					// f.s[i*n + j] = 0.0;
					f.u[i*n + j] += 0.2 * vx;
					f.u[(i+1)*n + j] += 0.2 * vx;
					f.v[i*n + j] += 0.2 * vy;
					f.v[i*n + j+1] += 0.2 * vy;
				}
			}
		}
	}

	// interaction -------------------------------------------------------

	var mouseDown = false;

	function startDrag(x, y) {
		let bounds = canvas.getBoundingClientRect();

		let mx = x - bounds.left - canvas.clientLeft;
		let my = y - bounds.top - canvas.clientTop;
		mouseDown = true;

		x = mx / cScale;
		y = (canvas.height - my) / cScale;

		setObstacle(x,y, true);
	}

	function drag(x, y) {
		if (mouseDown) {
			let bounds = canvas.getBoundingClientRect();
			let mx = x - bounds.left - canvas.clientLeft;
			let my = y - bounds.top - canvas.clientTop;
			x = mx / cScale;
			y = (canvas.height - my) / cScale;
			setObstacle(x,y, false);
		}
	}

	function endDrag() {
		mouseDown = false;
	}

	canvas.addEventListener('mousedown', event => {
		startDrag(event.x, event.y);
	});

	canvas.addEventListener('mouseup', event => {
		endDrag();
	});

	canvas.addEventListener('mousemove', event => {
		drag(event.x, event.y);
	});

	canvas.addEventListener('touchstart', event => {
		startDrag(event.touches[0].clientX, event.touches[0].clientY)
	});

	canvas.addEventListener('touchend', event => {
		endDrag()
	});

	canvas.addEventListener('touchmove', event => {
		event.preventDefault();
		event.stopImmediatePropagation();
		drag(event.touches[0].clientX, event.touches[0].clientY)
	}, { passive: false});


	document.addEventListener('keydown', event => {
		switch(event.key) {
			case 'p': scene.paused = !scene.paused; break;
			case 'm': scene.paused = false; simulate(); scene.paused = true; break;
		}
	});

	function toggleStart()
	{
		var button = document.getElementById('startButton');
		if (scene.paused)
			button.innerHTML = "Stop";
		else
			button.innerHTML = "Start";
		scene.paused = !scene.paused;
	}

	document.getElementById("probabilitySlider").oninput = function() {
		scene.swirlProbability = this.value;
	}

	var resizeTimer = 0;
	
	onResize = function() {
    	clearTimeout(resizeTimer);
		resizeTimer = setTimeout(setupScene, 300);
	};

	// main -------------------------------------------------------

	function simulate() 
	{
		if (!scene.paused)
			scene.fluid.simulate(scene.dt, scene.gravity, scene.numIters)
			scene.frameNr++;
	}

	function update() {
		simulate();
		draw();
		requestAnimationFrame(update);
	}

	setupScene();
	
	update();
	
</script> 
</body>
</html>