dhteumeuleu » Fluid dynamics

Fluid dynamics

On May 13, 2011, in lab, by ge1doot

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Direct Link

Download: http://www.dhteumeuleu.com/dhtml/water-js-canvas.html

Source code

<!DOCTYPE html> 
<html> 
<head> 
<title>Fluid dynamics - Interactive DHTML demos</title> 
<meta name="Author" content="Gerard Ferrandez at http://www.dhteumeuleu.com"> 
<style type="text/css"> 
	body { 
		margin: 0px; 
		padding: 0px; 
		background: #111; 
		width: 100%; 
		height: 100%; 
		color:#fff; 
		font-size:12px; 
		font-family: arial,verdana; 
	} 
	#screen { 
		position: absolute; 
		left: 50%; 
		top: 50%; 
		background: #000; 
		overflow: hidden; 
		width: 400px; 
		height: 400px; 
		margin-left:-200px; 
		margin-top:-200px; 
		outline: #222 solid 1px; 
	} 
	#screen img { 
		position: absolute; 
	} 
	#particle { 
		visibility: hidden; 
	} 
	#fps { 
		position: absolute; 
		left: 50%; 
		top: 50%; 
		width: 400px; 
		margin-top: 205px; 
		margin-left:-200px; 
		text-align: right; 
		color:#666; 
	} 
</style> 
 
<script type="text/javascript"> 
// =============================================================================== 
//              ***** Particle-based JS Fluid Simulation ***** 
// ----------------------------------------------------------------------------- 
// JavaScript: Gerard Ferrandez - 8 May 2011 
// http://www.dhteumeuleu.com/ 
// use under a CC-BY-NC license 
// ----------------------------------------------------------------------------- 
// Freely adapted from Grant Kot visco-elastic Java implementation 
// http://kotsoft.googlepages.com/Viscoelastic2.html 
// Research paper - 
// http://www.iro.umontreal.ca/labs/infographie/papers/Clavet-2005-PVFS/pvfs.pdf 
// =============================================================================== 
 
"use strict"; 
 
(function () { 
	// ----- private vars ----- 
	var canvas, ctx, nw, nh, nx, ny, nbX, nbY, particleImage, particleWidth, particleHeight, 
		particles = [], grid = [], neighbors = [], mousePressed, 
		mouseX = 0, mouseY = 0, fps = 0, nParticles, gridResolution, rad; 
	// ----- Particle prototype ----- 
	var Particle = function (x, y) { 
		this.x = x; 
		this.y = y; 
		this.pprevx = x; 
		this.pprevy = y; 
		this.velx = 0; 
		this.vely = 0; 
	}; 
	Particle.prototype.pass1 = function () { 
		// ----- maintain spatial hashing grid ------ 
		var g = grid[Math.round(this.y / gridResolution) * nbX + Math.round(this.x / gridResolution)]; 
		g.neighborsParticles[g.len++] = this; 
		// ----- mouse pressed ----- 
		if (mousePressed) { 
			var vx = this.x - mouseX; 
			var vy = this.y - mouseY; 
			var vlen = Math.sqrt(vx * vx + vy * vy); 
			if (vlen >= 1 && vlen < 60) { 
				this.velx += 0.5 * rad * (vx / vlen) / vlen; 
				this.vely += 0.5 * rad * (vy / vlen) / vlen; 
			} 
		} 
		// apply gravity 
		this.vely += 0.01; 
		// save previous position 
		this.pprevx  = this.x; 
		this.pprevy  = this.y; 
		// advance to predicted position 
		this.x += this.velx; 
		this.y += this.vely; 
	} 
	// ----- Double Density Relaxation Algorithm ----- 
	Particle.prototype.pass2 = function () { 
		var pressure = 0, presnear = 0, nl = 0; 
		// ----- get grid position ----- 
		var xc = Math.round(this.x / gridResolution); 
		var yc = Math.round(this.y / gridResolution); 
		// ----- 3 x 3 grid cells ----- 
		for (var xd = -1; xd < 2; xd++){ 
			for (var yd = -1; yd < 2; yd++){ 
				var h = grid[(yc + yd) * nbX + (xc + xd)]; 
				if (h && h.len) { 
					// ----- foreach neighbors pair ----- 
					for (var a = 0, l = h.len; a < l; a++) { 
						var pn = h.neighborsParticles[a]; 
						if (pn != this) { 
							var vx = pn.x - this.x; 
							var vy = pn.y - this.y; 
							var vlen = Math.sqrt(vx * vx + vy * vy); 
							if (vlen < rad){ 
								// ----- compute density and near-density ----- 
								var q = 1 - (vlen / rad); 
								pressure += q * q; // quadratic spike 
								presnear += q * q * q; // cubic spike 
								pn.q = q; 
								pn.vxl = (vx / vlen) * q; 
								pn.vyl = (vy / vlen) * q; 
								neighbors[nl++] = pn; 
							} 
						} 
					} 
				} 
			} 
		} 
		// ----- screen limits ----- 
		if (this.x < rad){ 
			var q = 1 - Math.abs(this.x / rad); 
			this.x += q * q * 0.5; 
		} else if (this.x > nw - rad){ 
			var q = 1 - Math.abs((nw - this.x) / rad); 
			this.x -= q * q * 0.5; 
		} 
		if (this.y < rad){ 
			var q = 1 - Math.abs(this.y / rad); 
			this.y += q * q * 0.5; 
		} else if (this.y > nh - rad){ 
			var q = 1 - Math.abs((nh - this.y) / rad); 
			this.y -= q * q * 0.5; 
		} 
		if (this.x < particleWidth) this.x = particleWidth; else if (this.x > nw - particleWidth) this.x = nw - particleWidth; 
		if (this.y < particleHeight) this.y = particleHeight; else if (this.y > nh - particleHeight) this.y = nh - particleHeight; 
		// ----- second pass of the relaxation ----- 
		pressure = (pressure - 3) * 0.5; 
		presnear *= 0.5; 
		for (var a = 0; a < nl; a++){ 
			var np = neighbors[a]; 
			// apply displacements 
			var p = pressure + presnear * np.q; 
			var dx = (np.vxl * p) * 0.5; 
			var dy = (np.vyl * p) * 0.5; 
			np.x += dx; 
			np.y += dy; 
			this.x -= dx; 
			this.y -= dy; 
		} 
	} 
	Particle.prototype.pass3 = function () { 
		// use previous position to compute next velocity 
		this.velx = this.x - this.pprevx; 
		this.vely = this.y - this.pprevy; 
		// draw particles - HTML5 canvas drawImage 
		ctx.drawImage(particleImage, this.x - particleWidth, this.y - particleHeight); 
	} 
	// ----- main loop ----- 
	var run = function () { 
		ctx.clearRect(0, 0, nw, nh); 
		// ----- reset grid ----- 
		for (var i = 0, l = nbX * nbY; i < l; i++) grid[i].len = 0; 
		// ----- simulation passes ----- 
		for (var i = 0; i < nParticles; i++) particles[i].pass1(); 
		for (var i = 0; i < nParticles; i++) particles[i].pass2(); 
		for (var i = 0; i < nParticles; i++) particles[i].pass3(); 
		fps++; 
	}; 
	//////////////////////////////////////////////////////////////////////////////////////// 
	// ----- initialization ----- 
	var init = function (params) { 
		// ----- entry parameters ----- 
		nParticles = params.nParticles; 
		gridResolution = params.gridResolution; 
		rad = params.rad; 
		// ----- DOM elements ----- 
		var d = canvas = document.getElementById("screen"); 
		ctx = canvas.getContext("2d"); 
		particleImage = document.getElementById("particle"); 
		particleWidth = particleImage.width * 0.5; 
		particleHeight = particleImage.height * 0.5; 
		// ---- canvas dimensions ---- 
		nw = d.offsetWidth; 
		nh = d.offsetHeight; 
		canvas.width = nw; 
		canvas.height = nh; 
		for (nx = 0, ny = 0; d != null; d = d.offsetParent) { 
			nx += d.offsetLeft; 
			ny += d.offsetTop; 
		} 
		nbX = Math.round(nw / gridResolution) + 1; 
		nbY = Math.round(nh / gridResolution) + 1; 
		// ----- init grid (static for better js performance) ----- 
		for (var i = 0; i < nbX * nbY; i++) { 
			grid[i] = { 
				len: 0, 
				neighborsParticles: [] 
			} 
		}; 
		// ----- create particles ----- 
		for (var i = 0; i < nParticles; i++ ) { 
			particles[i] = new Particle(Math.random() * nw, Math.random() * nh); 
		} 
		// ----- mouse events ----- 
		document.onselectstart = function () { return false; } 
		document.ondrag        = function () { return false; } 
		document.addEventListener('mousedown', function (e) { mousePressed = true;  }, false); 
		document.addEventListener('mouseup',   function (e) { mousePressed = false; }, false); 
		document.addEventListener('mousemove', function (e) { 
			mouseX = e.clientX - nx; 
			mouseY = e.clientY - ny; 
		}, false); 
		// ----- start engine ----- 
		setInterval(run, 16); 
		// ----- frames per second ----- 
		setInterval(function () { 
			document.getElementById('fps').innerHTML = fps + " fps"; 
			fps = 0; 
		}, 1000); 
	}; 
 
	return { 
		//////////////////////////////////////////////////////////////////////////// 
		// ---- launch script ----- 
		init : function (params) { 
			window.addEventListener('load', function () { 
				init(params); 
			}, false); 
		} 
	} 
})().init({ 
	// ----- init parameters ----- 
	nParticles:1000, 
	gridResolution: 20, 
	rad: 20 
}); 
</script> 
</head> 
<body> 
<canvas id="screen">If the brute force approach doesn't work, you're obviously not using enough brute force!</canvas> 
<div id="fps"></div> 
<img id = "particle" src="../images/bouton_green.png"> 
</body> 
</html>

Tagged with: canvas • fluid • particles • physics • water