本文作者html5tricks，转载请注明出处
还记得很早以前向大家分享的这款HTML5 Canvas模拟衣服撕扯动画吗？这绝对是一款非常具有创意而且很好玩的
下面我们来简单分享一下实现的源码，代码主要由HTML和JavaScript组成，主要还是JavaScript。
HTML代码：
只是定义了一个canvas标签，非常简单。
JavaScript代码：
canvas = document.getElementById('c');
ctx = canvas.getContext('2d');
//settings
var physics_acc = 5,
tear_distance = 40,
auto_rotate = 1,
field_of_view = 500,
gravity = 0.2,
friction = 0.99,
cloth_rows = 20,
pm_locked_c = 39; //pointmass locked count - prevents the cloth from falling to the ground
//arrays
var pointmass = [],
constraints = [];
vertex = [];
//random
var halfx = canvas.width / 2,
halfy = canvas.height / 2,
rotatex = 0,
rotatey = 0,
rotatez = 0,
mouse = {
down: false,
x: 0,
y: 0,
ox: 0,
oy: 0,
button: 0
};
ctx.lineWidth = 0.5;
ctx.strokeStyle = "#ddd";
window.requestAnimFrame =
window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function (callback) {
window.setTimeout(callback, 1000 / 60);
};
function init() {
//create top row
for(i = 0; i < 40; i++) {
x = Math.cos(2 * Math.PI * (i / 40)) * 100;
z = Math.sin(2 * Math.PI * (i / 40)) * 100;
create_pointmass(x, cloth_rows / 2 * -20, z);
}
//rest
for(i = 0; i < 40; i++) {
x = Math.cos(2 * Math.PI * (i / 40)) * 100;
z = Math.sin(2 * Math.PI * (i / 40)) * 100;
for(y = cloth_rows / 2 * -20 + 20; y < cloth_rows / 2 * 20; y+=20) {
create_pointmass(x,y,z);
}
}
//create constraints based on distance
for(i = 0; i < pointmass.length; i++) {
for(c = i + 1; c < pointmass.length; c++) {
dist = Math.sqrt(
Math.pow(pointmass[i][0] - pointmass[c][0], 2)
+ Math.pow(pointmass[i][1] - pointmass[c][1], 2)
+ Math.pow(pointmass[i][2] - pointmass[c][2], 2));
if(dist < 21) {
create_constraint(i,c);
}
}
}
//mouse
canvas.onmousemove = function(e) {
mouse.ox = mouse.x;
mouse.oy = mouse.y;
mouse.x = e.pageX - canvas.offsetLeft,
mouse.y = e.pageY - canvas.offsetTop;
e.preventDefault();
};
canvas.onmousedown = function(e) {
mouse.button = e.which;
mouse.down = true;
e.preventDefault();
};
canvas.oncontextmenu = function(e) {
e.preventDefault();
};
canvas.onmouseup = function(e) {
mouse.down = false;
e.preventDefault();
};
render()
}
function draw3D() {
vertex = [];
for(i = 0; i < pointmass.length; i++) {
vertex.push([pointmass[i][0],pointmass[i][1],pointmass[i][2]])
}
if(auto_rotate == 1)rotatey+= 0.01;
for(i = 0; i < vertex.length; i++) {
xyz = vertex[i];
x = xyz[0];
y = xyz[1];
z = xyz[2];
xcosa = Math.cos(rotatex);
xsina = Math.sin(rotatex);
ycosa = Math.cos(rotatey);
ysina = Math.sin(rotatey);
zcosa = Math.cos(rotatez);
zsina = Math.sin(rotatez);
xy = xcosa*y - xsina*z; //x
xz = xsina*y + xcosa*z;
yz = ycosa*xz - ysina*x; //y
yx = ysina*xz + ycosa*x;
zx = zcosa*yx - zsina*xy; //z
zy = zsina*yx + zcosa*xy;
xyz[0] = zx;
xyz[1] = zy;
xyz[2] = yz;
}
ctx.beginPath();
for(i = 0; i < constraints.length; i++) {
for(c = 0; c < 2; c++) {
xyz = vertex[constraints[i][c]];
fov = field_of_view / (field_of_view + xyz[2]);
x = xyz[0] * fov + halfx;
y = xyz[1] * fov + halfy;
if(c == 0) {
ctx.moveTo(x,y);
} else {
ctx.lineTo(x,y);
}
}
}
ctx.closePath();
ctx.stroke();
}
function update_pointmass() {
for(i = 0; i < pointmass.length; i++) {
x = pointmass[i][0];
y = pointmass[i][1];
z = pointmass[i][2];
ox = pointmass[i][3];
oy = pointmass[i][4];
oz = pointmass[i][5];
dx = x - ox;
dy = y - oy;
dz = z - oz;
if(i > pm_locked_c) {
pointmass[i][3] = x;
pointmass[i][4] = y;
pointmass[i][5] = z;
pointmass[i][0] = x + dx * friction;
pointmass[i][1] = y + dy + gravity;
pointmass[i][2] = z + dz * friction;
} else {
pointmass[i][0] = ox;
pointmass[i][1] = oy;
pointmass[i][2] = oz;
}
}
}
function update_constraint() {
for(i = 0; i < physics_acc; i++) {
for(c = 0; c < constraints.length; c++) {
c1 = pointmass[constraints[c][0]];
c2 = pointmass[constraints[c][1]];
diffx = c1[0] - c2[0];
diffy = c1[1] - c2[1];
diffz = c1[2] - c2[2];
dist = Math.sqrt(diffx * diffx + diffy * diffy + diffz * diffz);
diff = (constraints[c][2] - dist) / dist;
dx = c1[0] - c2[0];
dy = c1[1] - c2[1];
dz = c1[2] - c2[2];
dx = dx * 0.5;
dy = dy * 0.5;
dz = dz * 0.5;
c1[0] = c1[0] + dx * diff;
c1[1] = c1[1] + dy * diff;
c1[2] = c1[2] + dz * diff;
c2[0] = c2[0] - dx * diff;
c2[1] = c2[1] - dy * diff;
c2[2] = c2[2] - dz * diff;
constraints[c][3] = dist;
if(dist > tear_distance) {
constraints.splice(c, 1);
}
}
}
}
function create_pointmass(x,y,z) {
pointmass.push([x, y, z, x, y, z]);
}
function create_constraint(f,s) {
constraints.push([f, s, Math.sqrt(
Math.pow((pointmass[f][0] - pointmass[s][0]), 2)
+ Math.pow((pointmass[f][1] - pointmass[s][1]), 2)
+ Math.pow((pointmass[f][2] - pointmass[s][2]), 2)), 1])
}
function render() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
update_mouse();
update_pointmass();
update_constraint();
draw3D();
requestAnimFrame(render);
}
function update_mouse() {
if(mouse.down == true) {
for(i = 0; i < pointmass.length; i++) {
dist = Math.sqrt(Math.pow((vertex[i][0] - (mouse.x - halfx)), 2)
+ Math.pow((vertex[i][1] - (mouse.y - halfy)), 2)
+ Math.pow((vertex[i][2] + 50), 2));
if(dist < 100 && mouse.button == 1) {
pointmass[i][3] = pointmass[i][3] - Math.min(1, (mouse.x - mouse.ox) / 10);
pointmass[i][4] = pointmass[i][4] - Math.min(1, (mouse.y - mouse.oy) / 10);
}
//lazy cut for m2
if(dist < 21 && mouse.button == 3) {
pointmass[i][4] = -1000;
pointmass[i][3] = -1000;
}
}
}
}
最后在页面加载完后调用一下初始化的代码即可：
init();