相关主题：requestAnimationFrame 垃圾回收
我一直致力于在我为触摸设备构建的小部件中实现流畅的动画，我发现可以帮助我实现这一目标的工具之一是 Chrome 内存时间轴屏幕。
评估我在 rAF 循环中的内存消耗对我有点帮助，但我对我在 Chrome 30 中观察到的一些行为方面感到困扰。
最初进入运行 rAF 循环的页面时，我看到了这一点。
看起来还可以。如果我完成了工作并消除了内部循环中的对象分配，就不应该有锯齿。这是与链接主题一致的行为，也就是说，只要您使用 rAF，Chrome 就会内置泄漏。（哎呀！）
当我开始在页面中做各种事情时，它会变得更有趣。
我并没有真正做任何不同的事情，只是暂时添加了两个元素，这些元素将 CSS3 3D 变换样式应用于几帧，然后我停止与它们交互。
我们在这里看到的是 Chrome 报告突然每次 rAF 触发（16 毫秒）都会导致Animation Frame Fired x 3.
这种重复，以及它这样做的速率，单调增加，直到页面刷新。
您已经可以在第二个屏幕截图中看到锯齿斜率在最初从 跳转Animation Frame Fired到后急剧增加Animation Frame Fired x 3。
过了一会儿，它跳到了x 21：
看起来我的代码运行了一大堆额外的时间，但所有额外的多次运行只是浪费热量，丢弃了计算。
当我拍摄第三个屏幕截图时，我的 Macbook 发热非常严重。不久之后，在我能够将时间线拖到最后一点（大约 8 分钟）以查看x数字增加到什么之前，检查器窗口变得完全没有响应，并且提示我我的页面变得没有响应并且必须终止。
以下是页面中运行的全部代码：
// ============================================================================
// Copyright (c) 2013 Steven Lu
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.
// ============================================================================
// This is meant to be a true velocity verlet integrator, which means sending
// in for the force and torque a function (not a value). If the forces provided
// are evaluated at the current time step then I think we are left with plain
// old Euler integration. This is a 3 DOF integrator that is meant for use
// with 2D rigid bodies, but it should be equally useful for modeling 3d point
// dynamics.
// this attempts to minimize memory waste by operating on state in-place.
function vel_verlet_3(state, acc, dt) {
var x = state[0],
y = state[1],
z = state[2],
vx = state[3],
vy = state[4],
vz = state[5],
ax = state[6],
ay = state[7],
az = state[8],
x1 = x + vx * dt + 0.5 * ax * dt * dt,
y1 = y + vy * dt + 0.5 * ay * dt * dt,
z1 = z + vz * dt + 0.5 * az * dt * dt, // eqn 1
a1 = acc(x1, y1, z1),
ax1 = a1[0],
ay1 = a1[1],
az1 = a1[2];
state[0] = x1;
state[1] = y1;
state[2] = z1;
state[3] = vx + 0.5 * (ax + ax1) * dt,
state[4] = vy + 0.5 * (ay + ay1) * dt,
state[5] = vz + 0.5 * (az + az1) * dt; // eqn 2
state[6] = ax1;
state[7] = ay1;
state[8] = az1;
}
// velocity indepedent acc --- shit this is gonna need to change soon
var acc = function(x, y, z) {
return [0,0,0];
};
$("#lock").click(function() {
var values = [Number($('#ax').val()), Number($('#ay').val()), Number($('#az').val())];
acc = function() {
return values;
};
});
// Obtain the sin and cos from an angle.
// Allocate nothing.
function getRotation(angle, cs) {
cs[0] = Math.cos(angle);
cs[1] = Math.sin(angle);
}
// Provide the localpoint as [x,y].
// Allocate nothing.
function global(bodystate, localpoint, returnpoint) {
getRotation(bodystate[2], returnpoint);
// now returnpoint contains cosine+sine of angle.
var px = bodystate[0], py = bodystate[1];
var x = localpoint[0], y = localpoint[1];
// console.log('global():', cs, [px, py], localpoint, 'with', [x,y]);
// [ c -s px ] [x]
// [ s c py ] * [y]
// [1]
var c = returnpoint[0];
var s = returnpoint[1];
returnpoint[0] = c * x - s * y + px;
returnpoint[1] = s * x + c * y + py;
}
function local(bodystate, globalpoint, returnpoint) {
getRotation(bodystate[2], returnpoint);
// now returnpoint contains cosine+sine of angle
var px = bodystate[0], py = bodystate[1];
var x = globalpoint[0], y = globalpoint[1];
// console.log('local():', cs, [px, py], globalpoint, 'with', [x,y]);
// [ c s ] [x - px]
// [ -s c ] * [y - py]
var xx = x - px, yy = y - py;
var c = returnpoint[0], s = returnpoint[1];
returnpoint[0] = c * xx + s * yy;
returnpoint[1] = -s * xx + c * yy;
}
var cumulativeOffset = function(element) {
var top = 0, left = 0;
do {
top += element.offsetTop || 0;
left += element.offsetLeft || 0;
element = element.offsetParent;
} while (element);
return {
top: top,
left: left
};
};
// helper to create/assign position debugger (handles a single point)
// offset here is a boundingclientrect offset and needs window.scrollXY correction
var hasDPOffsetRun = false;
var dpoff = false;
function debugPoint(position, id, color, offset) {
if (offset) {
position[0] += offset.left;
position[1] += offset.top;
}
// if (position[0] >= 0) { console.log('debugPoint:', id, color, position); }
var element = $('#point' + id);
if (!element.length) {
element = $('<div></div>')
.attr('id', 'point' + id)
.css({
pointerEvents: 'none',
position: 'absolute',
backgroundColor: color,
border: '#fff 1px solid',
top: -2,
left: -2,
width: 2,
height: 2,
borderRadius: 300,
boxShadow: '0 0 6px 0 ' + color
});
$('body').append(
$('<div></div>')
.addClass('debugpointcontainer')
.css({
position: 'absolute',
top: 0,
left: 0
})
.append(element)
);
if (!hasDPOffsetRun) {
// determine the offset of the body-appended absolute element. body's margin
// is the primary offender that tends to throw a wrench into our shit.
var dpoffset = $('.debugpointcontainer')[0].getBoundingClientRect();
dpoff = [dpoffset.left + window.scrollX, dpoffset.top + window.scrollY];
hasDPOffsetRun = true;
}
}
if (dpoff) {
position[0] -= dpoff[0];
position[1] -= dpoff[1];
}
// set position
element[0].style.webkitTransform = 'translate3d(' + position[0] + 'px,' + position[1] + 'px,0)';
}
var elements_tracked = [];
/*
var globaleventhandler = function(event) {
var t = event.target;
if (false) { // t is a child of a tracked element...
}
};
// when the library is loaded the global event handler for GRAB is not
// installed. It is lazily installed when GRAB_global is first called, and so
// if you only ever call GRAB then the document does not get any handlers
// attached to it. This will remain unimplemented as it's not clear what the
// semantics for defining behavior are. It's much more straightforward to use
// the direct API
function GRAB_global(element, custom_behavior) {
// this is the entry point that will initialize a grabbable element all state
// for the element will be accessible through its __GRAB__ element through
// the DOM, and the DOM is never accessed (other than through initial
// assignment) by the code.
// event handlers are attached to the document, so use GRAB_direct if your
// webpage relies on preventing event bubbling.
if (elements_tracked.indexOf(element) !== -1) {
console.log('You tried to call GRAB() on an element more than once.',
element, 'existing elements:', elements_tracked);
}
elements_tracked.push(element);
if (elements_tracked.length === 1) { // this is the initial call
document.addEventListener('touchstart', globaleventhandler, true);
document.addEventListener('mousedown', globaleventhandler, true);
}
}
// cleanup function cleans everything up, returning behavior to normal.
// may provide a boolean true argument to indicate that you want the CSS 3D
// transform value to be cleared
function GRAB_global_remove(cleartransform) {
document.removeEventListener('touchstart', globaleventhandler, true);
document.removeEventListener('mousedown', globaleventhandler, true);
}
*/
var mousedownelement = false;
var stop = false;
// there is only one mouse, and the only time when we need to handle release
// of pointer is when the one mouse is let go somewhere far away.
function GRAB(element, onfinish, center_of_mass) {
// This version directly assigns the event handlers to the element
// it is less efficient but more "portable" and self-contained, and also
// potentially more friendly by using a regular event handler rather than
// a capture event handler, so that you can customize the grabbing behavior
// better and also more easily define it per element
var offset = center_of_mass;
var pageOffset = cumulativeOffset(element);
var bcrOffset = element.getBoundingClientRect();
bcrOffset = {
left: bcrOffset.left + window.scrollX,
right: bcrOffset.right + window.scrollX,
top: bcrOffset.top + window.scrollY,
bottom: bcrOffset.bottom + window.scrollY
};
if (!offset) {
offset = [element.offsetWidth / 2, element.offsetHeight / 2];
}
var model = {
state: [0, 0, 0, 0, 0, 0, 0, 0, 0],
offset: offset,
pageoffset: bcrOffset // remember, these values are pre-window.scroll[XY]-corrected
};
element.__GRAB__ = model;
var eventhandlertouchstart = function(event) {
// set
var et0 = event.touches[0];
model.anchor = [0,0];
local(model.state, [et0.pageX - bcrOffset.left - offset[0], et0.pageY - bcrOffset.top - offset[1]], model.anchor);
debugPoint([et0.pageX, et0.pageY], 1, 'red');
event.preventDefault();
requestAnimationFrame(step);
};
var eventhandlermousedown = function(event) {
console.log('todo: reject right clicks');
// console.log('a', document.body.scrollLeft);
// set
// model.anchor = [event.offsetX - offset[0], event.offsetY - offset[1]];
model.anchor = [0,0];
var globalwithoffset = [event.pageX - bcrOffset.left - offset[0], event.pageY - bcrOffset.top - offset[1]];
local(model.state, globalwithoffset, model.anchor);
debugPoint([event.pageX, event.pageY], 1, 'red');
mousedownelement = element;
requestAnimationFrame(step);
};
var eventhandlertouchend = function(event) {
// clear
model.anchor = false;
requestAnimationFrame(step);
};
element.addEventListener('touchstart', eventhandlertouchstart, false);
element.addEventListener('mousedown', eventhandlermousedown, false);
element.addEventListener('touchend', eventhandlertouchend, false);
elements_tracked.push(element);
// assign some favorable properties to grabbable element.
element.style.webkitTouchCallout = 'none';
element.style.webkitUserSelect = 'none';
// TODO: figure out the proper values for these
element.style.MozUserSelect = 'none';
element.style.msUserSelect = 'none';
element.style.MsUserSelect = 'none';
}
document.addEventListener('mouseup', function() {
if (mousedownelement) {
mousedownelement.__GRAB__.anchor = false;
mousedownelement = false;
requestAnimationFrame(step);
}
}, false);
function GRAB_remove(element, cleartransform) {}
// unimpld
function GRAB_remove_all(cleartransform) {}
GRAB($('#content2')[0]);
(function() {
var requestAnimationFrame = window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame ||
window.requestAnimationFrame;
window.requestAnimationFrame = requestAnimationFrame;
})();
var now = function() { return window.performance ? performance.now() : Date.now(); };
var lasttime = 0;
var abs = Math.abs;
var dt = 0;
var scratch0 = [0,0];
var scratch1 = [0,0]; // memory pool
var step = function(time) {
dt = (time - lasttime) * 0.001;
if (time < 1e12) {
// highres timer
} else {
// ms since unix epoch
if (dt > 1e9) {
dt = 0;
}
}
// console.log('dt: ' + dt);
lasttime = time;
var foundnotstopped = false;
for (var i = 0; i < elements_tracked.length; ++i) {
var e = elements_tracked[i];
var data = e.__GRAB__;
if (data.anchor) {
global(data.state, data.anchor, scratch0);
scratch1[0] = scratch0[0] + data.offset[0];
scratch1[1] = scratch0[1] + data.offset[1];
//console.log("output of global", point);
debugPoint(scratch1,
0, 'blue', data.pageoffset);
} else {
scratch1[0] = -1000;
scratch1[1] = -1000;
debugPoint(scratch1, 0, 'blue');
}
// timestep is dynamic and based on reported time. clamped to 100ms.
if (dt > 0.3) {
//console.log('clamped from ' + dt + ' @' + now());
dt = 0.3;
}
vel_verlet_3(data.state, acc, dt);
e.style.webkitTransform = 'translate3d(' + data.state[0] + 'px,' + data.state[1] + 'px,0)' +
'rotateZ(' + data.state[2] + 'rad)';
}
requestAnimationFrame(step);
};
requestAnimationFrame(step);
为了完整起见，这里是测试页面 HTML：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta http-equiv="cache-control" content="max-age=0" />
<meta http-equiv="cache-control" content="no-cache" />
<meta http-equiv="expires" content="0" />
<meta http-equiv="expires" content="Tue, 01 Jan 1980 1:00:00 GMT" />
<meta http-equiv="pragma" content="no-cache" />
<title>symplectic integrator test page</title>
<script src="zepto.js"></script>
<script src="d3.v3.js"></script>
<style type='text/css'>
body {
position: relative;
margin: 80px;
}
#content {
width: 800px;
height: 40px;
display: inline-block;
background: lightgreen;
padding: 20px;
margin: 30px;
border: green dashed 1px;
}
#content2 {
top: 200px;
width: 600px;
height: 200px;
display: inline-block;
background: lightblue;
padding: 20px;
margin: 30px;
border: blue dashed 1px;
}
</style>
</head>
<body>
<div id='scrolling-placeholder' style='background-color: #eee; height: 1000px;'></div>
<label>dt:<input id='dt' type='number' step='0.001' value='0.016666666' /></label>
<label>ax:<input id='ax' type='number' step='0.25' value='0' /></label>
<label>ay:<input id='ay' type='number' step='0.25' value='0' /></label>
<label>t:<input id='az' type='number' step='0.01' value='0' /></label>
<button id='lock'>Set</button>
<button id='zerof' onclick='$("#ax,#ay,#az").val(0);'>Zero forces</button>
<button id='zerov'>Zero velocities</button>
<div>
<span id='content'>content</span>
<span id='content2'>content2</span>
</div>
<div id='debuglog'></div>
<script src="rb2.js"></script>
</body>
</html>
这应该满足任何“向我们展示代码”的要求。
现在我不会赌上我的生命，但我很确定我至少在正确使用 rAF 方面做得很好。我没有滥用任何东西，我已经改进了代码，使其对 Javascript 内存分配非常轻。
所以，真的， Chrome绝对没有理由接受这个并试图像火箭一样将我的笔记本电脑送入轨道。没理由。
一般来说，Safari 似乎处理得更好（它最终不会死），而且我会注意到 iOS 通常能够保持 200x600px 的 div 以 60fps 的速度平移和旋转。
但是，我承认我还没有看到 Chrome 真的像这样死去，除非我让它记录了内存时间线。
在这一点上，我有点摸不着头脑。这可能只是与这个特定的开发工具功能（据我所知，这是同类产品中唯一的一个）的一些意外的、不可预见的交互。
所以然后我尝试了一些新的东西，至少可以帮助调查内存时间线额外回调触发的这个问题：
添加了这些行。
window.rafbuf = [];
var step = function(time) {
window.rafbuf.push(time);
这基本上注销了我的 rAF 例程（step()函数）被调用的所有时间。
当它正常运行时，它大约每 16.7 毫秒记录一次时间。
我懂了：
这清楚地表明它使用相同的时间输入参数重新运行step()至少 22 次，就像时间线试图告诉我的那样。
所以我敢让你，互联网，告诉我这是有意的行为。:)