某人用Java搞了一个流体力学的演示：http://grantkot.com/MPM/Liquid.html。

下面是 HTML 5版的流体力学演示（推荐使用Chrome浏览器浏览）：

效果演示

<canvas width="400" height="400" id="liquid"></canvas><script> /** * This version: * Copyright Stephen Sinclair (radarsat1) ( http://www.music.mcgill.ca/~sinclair ) * MIT License ( http://www.opensource.org/licenses/mit-license.php ) * Downloaded from: http://www.music.mcgill.ca/~sinclair/blog */ /** * Flash version: * Copyright iunpin ( http://wonderfl.net/user/iunpin ) * MIT License ( http://www.opensource.org/licenses/mit-license.php ) * Downloaded from: http://wonderfl.net/c/6eu4 */ /** * Original Java version: * http://grantkot.com/MPM/Liquid.html */ var canvas;var context;var running = false;var width = 0;var height = 0;var liquidTest;var step = 0; function LiquidTest(gsizeX, gsizeY, particlesX, particlesY){ this.particles = []; this.gsizeX = gsizeX; this.gsizeY = gsizeY; this.grid = [[]]; //Nodes this.active = []; //Nodes this.water = new Material(1.0, 1.0, 1.0, 1.0, 1.0, 1.0); this.pressed = false; this.pressedprev = false; this.mx = 0; this.my = 0; this.mxprev = 0; this.myprev = 0; this.init = function() { var i = 0, j = 0; this.grid = []; for (i = 0; i < this.gsizeX; i++) { this.grid.push([]); for (j = 0; j < this.gsizeY; j++) { this.grid[i].push(new Node()); } } var p; for (i = 0; i < particlesX; i++) for (j = 0; j < particlesY; j++) { p = new Particle(this.water, i + 4, j + 4, 0.0, 0.0); this.particles.push(p); } } this.paint = function() { context.clearRect(0, 0, width, height); context.beginPath(); for (var pi in this.particles) { var p = this.particles[pi]; line(4.0 * p.x, 4.0 * p.y, 4.0 * (p.x - p.u), 4.0 * (p.y - p.v)); } context.stroke(); } this.simulate = function() { var drag = false; var mdx = 0.0, mdy = 0.0; if (this.pressed && this.pressedprev) { drag = true; mdx = 0.25 * (this.mx - this.mxprev); mdy = 0.25 * (this.my - this.myprev); } this.pressedprev = this.pressed; this.mxprev = this.mx; this.myprev = this.my; for (var n in this.active) this.active[n].clear(); this.active.length = 0; var i, j; var x, y, phi; var fx = 0.0, fy = 0.0; for (var pi in this.particles) { var p = this.particles[pi]; p.cx = parseInt(p.x - 0.5); p.cy = parseInt(p.y - 0.5); x = p.cx - p.x; p.px[0] = (0.5 * x * x + 1.5 * x + 1.125); p.gx[0] = (x + 1.5); x += 1.0; p.px[1] = (-x * x + 0.75); p.gx[1] = (-2.0 * x); x += 1.0; p.px[2] = (0.5 * x * x - 1.5 * x + 1.125); p.gx[2] = (x - 1.5); y = p.cy - p.y; p.py[0] = (0.5 * y * y + 1.5 * y + 1.125); p.gy[0] = (y + 1.5); y += 1.0; p.py[1] = (-y * y + 0.75); p.gy[1] = (-2.0 * y); y += 1.0; p.py[2] = (0.5 * y * y - 1.5 * y + 1.125); p.gy[2] = (y - 1.5); for (var i = 0; i < 3; i++) { for (var j = 0; j < 3; j++) { var n = this.grid[p.cx + i][p.cy + j]; if (!n.active) { this.active.push(n); n.active = true; } phi = p.px[i] * p.py[j]; n.m += phi * p.mat.m; n.d += phi; n.gx += p.gx[i] * p.py[j]; n.gy += p.px[i] * p.gy[j]; } } } var density, pressure, weight; var n01, n02; var n11, n12; var cx, cy; var cxi, cyi; var pdx, pdy; var C20, C02, C30, C03; var csum1, csum2; var C21, C31, C12, C13, C11; var u, u2, u3; var v, v2, v3; for (var pi in this.particles) { var p = this.particles[pi]; cx = parseInt(p.x); cy = parseInt(p.y); cxi = cx + 1; cyi = cy + 1; n01 = this.grid[cx][cy]; n02 = this.grid[cx][cyi]; n11 = this.grid[cxi][cy]; n12 = this.grid[cxi][cyi]; pdx = n11.d - n01.d; pdy = n02.d - n01.d; C20 = 3.0 * pdx - n11.gx - 2.0 * n01.gx; C02 = 3.0 * pdy - n02.gy - 2.0 * n01.gy; C30 = -2.0 * pdx + n11.gx + n01.gx; C03 = -2.0 * pdy + n02.gy + n01.gy; csum1 = n01.d + n01.gy + C02 + C03; csum2 = n01.d + n01.gx + C20 + C30; C21 = 3.0 * n12.d - 2.0 * n02.gx - n12.gx - 3.0 * csum1 - C20; C31 = -2.0 * n12.d + n02.gx + n12.gx + 2.0 * csum1 - C30; C12 = 3.0 * n12.d - 2.0 * n11.gy - n12.gy - 3.0 * csum2 - C02; C13 = -2.0 * n12.d + n11.gy + n12.gy + 2.0 * csum2 - C03; C11 = n02.gx - C13 - C12 - n01.gx; u = p.x - cx; u2 = u * u; u3 = u * u2; v = p.y - cy; v2 = v * v; v3 = v * v2; density = n01.d + n01.gx * u + n01.gy * v + C20 * u2 + C02 * v2 + C30 * u3 + C03 * v3 + C21 * u2 * v + C31 * u3 * v + C12 * u * v2 + C13 * u * v3 + C11 * u * v; pressure = density - 1.0; if (pressure > 2.0) pressure = 2.0; fx = 0.0; fy = 0.0; if (p.x < 4.0) fx += p.mat.m * (4.0 - p.x); else if (p.x > this.gsizeX - 5) fx += p.mat.m * (this.gsizeX - 5 - p.x); if (p.y < 4.0) fy += p.mat.m * (4.0 - p.y); else if (p.y > this.gsizeY - 5) fy += p.mat.m * (this.gsizeY - 5 - p.y); if (drag) { var vx = Math.abs(p.x - 0.25 * this.mx); var vy = Math.abs(p.y - 0.25 * this.my); if ((vx < 10.0) && (vy < 10.0)) { weight = p.mat.m * (1.0 - vx * 0.10) * (1.0 - vy * 0.10); fx += weight * (mdx - p.u); fy += weight * (mdy - p.v); } } for (i = 0; i < 3; i++) { for (j = 0; j < 3; j++) { n = this.grid[(p.cx + i)][(p.cy + j)]; phi = p.px[i] * p.py[j]; n.ax += -((p.gx[i] * p.py[j]) * pressure) + fx * phi; n.ay += -((p.px[i] * p.gy[j]) * pressure) + fy * phi; } } } for (var ni in this.active) { var n = this.active[ni]; if (n.m > 0.0) { n.ax /= n.m; n.ay /= n.m; n.ay += 0.03; } } var mu, mv; for (var pi in this.particles) { var p = this.particles[pi]; for (i = 0; i < 3; i++) { for (j = 0; j < 3; j++) { n = this.grid[(p.cx + i)][(p.cy + j)]; phi = p.px[i] * p.py[j]; p.u += phi * n.ax; p.v += phi * n.ay; } } mu = p.mat.m * p.u; mv = p.mat.m * p.v; for (i = 0; i < 3; i++) { for (j = 0; j < 3; j++) { n = this.grid[(p.cx + i)][(p.cy + j)]; phi = p.px[i] * p.py[j]; n.u += phi * mu; n.v += phi * mv; } } } for (var ni in this.active) { var n = this.active[ni]; if (n.m > 0.0) { n.u /= n.m; n.v /= n.m; } } var gu, gv; for (var pi in this.particles) { var p = this.particles[pi]; gu = 0.0; gv = 0.0; for (var i = 0; i < 3; i++) { for (var j = 0; j < 3; j++) { var n = this.grid[(p.cx + i)][(p.cy + j)]; phi = p.px[i] * p.py[j]; gu += phi * n.u; gv += phi * n.v; } } p.x += gu; p.y += gv; p.u += 1.0 * (gu - p.u); p.v += 1.0 * (gv - p.v); if (p.x < 1.0) { p.x = (1.0 + Math.random() * 0.01); p.u = 0.0; } else if (p.x > this.gsizeX - 2) { p.x = (this.gsizeX - 2 - Math.random() * 0.01); p.u = 0.0; } if (p.y < 1.0) { p.y = (1.0 + Math.random() * 0.01); p.v = 0.0; } else if (p.y > this.gsizeY - 2) { p.y = (this.gsizeY - 2 - Math.random() * 0.01); p.v = 0.0; } } } this.init();} function Node(){ this.m = 0; this.d = 0; this.gx = 0; this.gy = 0; this.u = 0; this.v = 0; this.ax = 0; this.ay = 0; this.active = false; this.clear = function() { this.m = this.d = this.gx = this.gy = this.u = this.v = this.ax = this.ay = 0.0; this.active = false; }} function Particle(mat, x, y, u, v){ this.mat = mat; this.x = x; this.y = y; this.u = u; this.v = v; this.dudx = 0; this.dudy = 0; this.dvdx = 0; this.dvdy = 0; this.cx = 0; this.cy = 0; this.px = [0,0,0]; this.py = [0,0,0]; this.gx = [0,0,0]; this.gy = [0,0,0];} function Material(m, rd, k, v, d, g){ this.m = m; this.rd = rd; this.k = k; this.v = v; this.d = d; this.g = g;} function line(x1,y1,x2,y2) { context.moveTo(x1,y1); context.lineTo(x2,y2);} function getPosition(obj) { var p = obj.offsetParent; var left = obj.offsetLeft; var top = obj.offsetTop; if (p) { var pos = getPosition(p); left += pos[0]; top += pos[1]; } return [left, top];} function mouseMoved(event){ var pos = getPosition(canvas); liquidTest.mx = event.pageX - pos[0]; liquidTest.my = event.pageY - pos[1];} function mousePressed(event){ liquidTest.pressed = true;} function mouseReleased(event){ liquidTest.pressed = false;} function stop(){ running = false;} function start(){ running = true; draw();} function restart(gsizeX, gsizeY, particlesX, particlesY){ liquidTest = new LiquidTest(gsizeX, gsizeY, particlesX, particlesY); running = true; draw();} function draw(){ // clear // advance simulation liquidTest.simulate(); step ++;} function init() { canvas = document.getElementById(‘liquid‘); width = canvas.width; height = canvas.height; context = canvas.getContext(‘2d‘); context.strokeStyle = "#0000FF"; canvas.onmousedown = mousePressed; canvas.onmouseup = mouseReleased; canvas.onmousemove = mouseMoved; liquidTest = new LiquidTest(100, 100, 50, 50); start();} setInterval(draw, 33);setInterval("liquidTest.paint()", 33); init();</script>

不过，这仅仅是个开始。某同学将其发布上了reddit.com，于是，全世界的同学们开始给力了。郸城县殳海环保

Flash的开发者首先不服，搞了个 flash版（带源码）：http://wonderfl.net/c/yxe9

看到了Flash版，Javascript+HTML5的同学们也不干了，于是出现HTML5版（带源码）：http://www.music.mcgill.ca/~sinclair/content/blog/liquid_simulator_ported_to_canvas

不过性能慢了很多，所以，又有人优化了一下HTML5版的程序：http://jsbin.com/unovo4

SVG的同学们也不甘寂寞，不过，那真叫一个慢啊：http://ulo.pe/js-liquid-svg/

这个时候，C/C++同学出来了，使用SDL库也搞了一个：http://q3k.org/fluidsim.zip

短短几天里，被人重写成各种语言。

下面看看在HTML 5里面的实现：

HTML5 canvas流体力学效果