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CSS Animation Notes

CSS Transform

transform:

  • No affect on the CSS box model layout (excepts overflow).
  • No affect on display: inline element.
  • Affect the visual rendering.
  • Affect client rectangles exposed by Element Interface Extensions (getClientRects()/getBoundingClientRect()).
  • Affect after clip/clip-path: first clip/clip-path, then transform.
  • Create new stacking context.
  • Create new containing block for absolute/fixed positioned children.
  • <transform-function>+: 多重变换从右向左按顺序执行.

Translate Transform

translate()/translateX()/translateY()/translateZ()/translate3d():

.translate {
/* 往右偏移10px, 往下偏移20px */
transform: translate(10px, 20px);

/* 往右偏移10px */
transform: translateX(10px);

/* 往下偏移20px */
transform: translateY(20px);

/* 往左偏移自身宽度的一半, 往上偏移自身高度的一半 */
transform: translate(-50%, -50%);
}

Scale Transform

scale()/scaleX()/scaleY()/scaleZ()/scale3d():

.scale {
/* 水平放大 2 倍, 垂直缩小 1/2 */
transform: scale(2, 0.5);

/* 水平放大 2 倍 */
transform: scaleX(2);

/* 垂直缩小 1/2 */
transform: scaleY(0.5);

/* 水平翻转效果 */
transform: scaleX(-1);

/* 垂直翻转效果 */
transform: scaleY(-1);
}

Rotate Transform

rotate()/rotateX()/rotateY()/rotateZ()/rotate3d():

  • deg: degrees 角度 (00 ~ 360360^{\circ}).
  • grad: grads 百分度 (00 ~ 400400).
  • rad: radians 弧度 (1=180π1^{\circ} = \frac{180}{\pi}).
  • turn: turns 圈数.
.rotate {
/* 正值顺时针, 负值逆时针 */
transform: rotate(45deg);
transform: rotate(50grad);
transform: rotate(0.7854rad);
transform: rotate(0.25turn);
}

Skew Transform

skew()/skewX()/skewY():

.skew {
/* 水平切斜 10 度, 垂直切斜 20 度 */
transform: skew(10deg, 20deg);

/* 水平切斜10度 */
transform: skewX(10deg);

/* 垂直切斜20度 */
transform: skewY(20deg);
}

Skew Transform

Matrix Transform

matrix(a, b, c, d, e, f):

[acebdf001][xy1]    [ax+cy+ebx+dy+f1]\begin{bmatrix} a & c & e \\ b & d & f \\ 0 & 0 & 1 \end{bmatrix} \begin{bmatrix} x \\ y \\ 1 \end{bmatrix} \implies \begin{bmatrix} ax + cy + e \\ bx + dy + f \\ 1 \end{bmatrix} x=ax+cy+ey=bx+dy+f\begin{align} x' &= ax + cy + e \\ y' &= bx + dy + f \end{align}

Translate:

x=1x+0y+e=x+ey=0x+1y+f=y+f\begin{align} x' &= 1 \cdot x + 0 \cdot y + e &= x + e \\ y' &= 0 \cdot x + 1 \cdot y + f &= y + f \end{align}

Scale:

x=ax+0y+0=axy=0x+dy+0=dy\begin{align} x' &= a \cdot x + 0 \cdot y + 0 &= ax \\ y' &= 0 \cdot x + d \cdot y + 0 &= dy \end{align}

Rotate:

x=cosθxsinθyy=sinθx+cosθy\begin{align} x' &= \cos\theta \cdot x - \sin\theta \cdot y \\ y' &= \sin\theta \cdot x + \cos\theta \cdot y \end{align}

Skew:

x=x+tanθxyy=tanθyx+y\begin{align} x' &= x + \tan{\theta x} \cdot y \\ y' &= \tan{\theta y} \cdot x + y \end{align}
.matrix {
transform: matrix(1, 0, 0, 1, var(--translate-x), var(--translate-y));
transform: matrix(var(--scale-x), 0, 0, var(--scale-y), 0, 0);
transform: matrix(var(--cos), var(--sin), var(--sin-minus), var(--cos), 0, 0);
transform: matrix(1, var(--tan-y), var(--tan-x), 1, 0, 0);
}

Transform Origin

transform-origin change transform start point:

  • X offset: <length>/<percentage>/left/center/right.
  • Y offset: <length>/<percentage>/top/center/bottom.
  • Z offset: <length>.
.transform-origin {
/* One-value syntax, the other is `50%`/`center` */
transform-origin: 2px;
transform-origin: bottom;

/* x-offset | y-offset */
transform-origin: 3cm 2px;
transform-origin: left 2px;

/* x-offset | y-offset | z-offset */
transform-origin: 2px 30% 10px;
transform-origin: left 5px -3px;
}

Individual Transform

Individual transform property:

.element {
rotate: 90deg;
rotate: y 0.25turn;
rotate: z 1.57rad;
rotate: 1 1 1 90deg;
scale: 2;
scale: 2 0.5;
scale: 2 0.5 2;
translate: 50%;
translate: 100px 200px;
translate: 50% 105px;
translate: 50% 105px 5rem;
}

Transform Style

transform-style:

  • flat: initial value, 表示平面变换.
  • preserve-3d: 表示 3D 透视变换.

Transform Perspective

perspective3D 转换元素定义透视视图:

.parent {
perspective: 201px;
}
  • 设置的 translateZ 值越小, 则子元素大小越小 (因为元素远去, 我们眼睛看到的就会变小).
  • translateZ 值越大, 该元素也会越来越大.
  • translateZ 值非常接近 201 像素, 但是不超过 201 像素的时候 (如 200 像素). 该元素的大小就会撑满整个屏幕 (父辈元素没有 overflow: hidden 的限制).
  • translateZ 值再变大, 超过 201 像素的时候, 该元素看不见了.

Transform Perspective

Backface Visibility

.element {
backface-visibility: hidden;
}

当元素 rotateY(180deg) 时, 元素将被隐藏.

Transform Container

  • :hover should not add to transformed elements, :hover should add to parent element.
  • 3D 变换一般需要在容器元素上加上以下样式:
.transform-container {
perspective: 1024px;
transform-style: preserve-3d;
}

.front .back {
backface-visibility: hidden;
}

Transform Alignment

  • Keep translate(-50%, -50%) in keyframe transform property list when using it for alignment.
  • 父元素设置了 transform 变换, position: fixed 子元素固定定位失效.
  • 父元素设置了 transform 变换 + overflow: hidden, position: absolute 子元素会被剪裁.
  • 当变换绝对定位居中的元素时, 需要改变 transform-origin:
.rotate {
position: absolute;
top: 200px;
left: 50%;
transform: translateX(-50%);
transform-origin: left;
}

Transform Reference

CSS Transition

Transition Property

  • transition-property: all (initial value).
  • transition-duration.
  • transition-delay: 支持负值.
  • transition-timing-function: <easing-function>.
.element {
transition: property duration timing-function delay;
transition: all 0s ease 0s;
transition: transform 0.5s ease-in-out 0.2s;
}

@media only screen and (prefers-reduced-motion: reduce) {
.element {
transition: none;
}
}
Transition Background Images

transition 无法对 CSS 背景图像 (如渐变效果) 起效:

  • 可以通过 opacity/background-position 间接实现渐变图像的过渡动画.
  • 可以通过 CSS Houdini @property 快速实现渐变图像的过渡动画.

Transition Timing Function

<easing-function>:

  • liner.
  • <cubic-bezier-timing-function>:
    • ease: cubic-bezier(0.25, 0.1, 0.25, 1.0).
    • ease-in: cubic-bezier(0.42, 0, 1.0, 1.0).
    • ease-out: cubic-bezier(0, 0, 0.58, 1.0).
    • ease-in-out: cubic-bezier(0.42, 0, 0.58, 1.0).
    • cubic-bezier(<number [0,1]>, <number>, <number [0,1]>, <number>).
  • <step-timing-function>:
    • step-start.
    • step-end.
    • steps(<integer>[, jump-start | jump-end | jump-none | jump-both | start | end]?).
    • 可用 animated background-position + <step-timing-function> + image sprites 模拟 GIFs.
:root {
--ease-in-quad: cubic-bezier(0.55, 0.085, 0.68, 0.53);
--ease-in-cubic: cubic-bezier(0.55, 0.055, 0.675, 0.19);
--ease-in-quart: cubic-bezier(0.895, 0.03, 0.685, 0.22);
--ease-in-quint: cubic-bezier(0.755, 0.05, 0.855, 0.06);
--ease-in-expo: cubic-bezier(0.95, 0.05, 0.795, 0.035);
--ease-in-circ: cubic-bezier(0.6, 0.04, 0.98, 0.335);
--ease-out-quad: cubic-bezier(0.25, 0.46, 0.45, 0.94);
--ease-out-cubic: cubic-bezier(0.215, 0.61, 0.355, 1);
--ease-out-quart: cubic-bezier(0.165, 0.84, 0.44, 1);
--ease-out-quint: cubic-bezier(0.23, 1, 0.32, 1);
--ease-out-expo: cubic-bezier(0.19, 1, 0.22, 1);
--ease-out-circ: cubic-bezier(0.075, 0.82, 0.165, 1);
--ease-in-out-quad: cubic-bezier(0.455, 0.03, 0.515, 0.955);
--ease-in-out-cubic: cubic-bezier(0.645, 0.045, 0.355, 1);
--ease-in-out-quart: cubic-bezier(0.77, 0, 0.175, 1);
--ease-in-out-quint: cubic-bezier(0.86, 0, 0.07, 1);
--ease-in-out-expo: cubic-bezier(l, 0, 0, 1);
--ease-in-out-circ: cubic-bezier(0.785, 0.135, 0.15, 0.86);
}

Step Timing Function

Transition Direction

By specifying the transition on the element itself, define the transition to occur in both directions (hover on "enter" and hover off "exit").

Change transition when :hover etc state bring magic effect:

.menu-nav {
visibility: hidden;
transition: all 0.4s ease-in-out; /* Exit transition */
transform: translateX(-100%);
}

.menu-link {
opacity: 0;
transition: opacity 0.4s ease-in-out; /* Exit transition */
}

.menu-toggle:checked ~ .menu-nav {
visibility: visible;
transform: translateX(0);
}

.menu-toggle:checked ~ .menu-nav .menu-link {
opacity: 1;

/* Magic effect for delaying enter transition */
transition: opacity 0.4s ease-in-out 0.4s;
}

Transition Class Controls

With transition: opacity 0.5s set, first add .opacity-0 class, then replace it with .opacity-1 class. Transition animation get trigger as css style of element changed (class changed):

@media only screen and (prefers-reduced-motion: reduce) {
.element {
transition: none;
}
}

.element {
transition: opacity 0.5s;
}

/* before-enter -> enter -> before-leave -> leave */
.enter,
.before-leave {
opacity: 1;
}

.leave,
.before-enter {
opacity: 0;
}
div.classList.add('before-enter')

setTimeout(() => {
div.classList.remove('before-enter')
div.classList.add('enter')
}, 20)

Transition Internals

transition take effect only when browser detecting different styles between style stage.

// transition not working
panel.style.transform = 'scale(0)'
panel.style.transition = 'transform .5s'
// previous `transform` is empty
panel.style.transform = 'scale(1)'

// transition working
panel.style.transform = 'scale(0)'
panel.style.transition = 'transform .5s'
// previous `transform` is `scale(0)`
requestAnimationFrame(() => {
panel.style.transform = 'scale(1)'
})

// transition working
panel.style.transform = 'scale(0)'
// `getComputedStyle(element).property` trigger a new `style` stage
const computedTransform = getComputedStyle(panel).transform
panel.style.transition = 'transform .5s'
// previous `transform` is `scale(0)`
panel.style.transform = 'scale(1)'

CSS View Transitions

CSS view transitions API:

/**
* ::view-transition
* └─ ::view-transition-group(root)
* └─ ::view-transition-image-pair(root)
* ├─ ::view-transition-old(root)
* └─ ::view-transition-new(root)
* Old page view animates from opacity 1 to 0,
* while the new view animates from opacity 0 to 1,
* which is what creates the default cross-fade.
*/
function updateView(event) {
// Handle the difference in whether the event is fired on the <a> or the <img>.
const targetIdentifier = event.target.firstChild || event.target

const displayNewImage = () => {
const mainSrc = `${targetIdentifier.src.split('_th.jpg')[0]}.jpg`
galleryImg.src = mainSrc
galleryCaption.textContent = targetIdentifier.alt
}

// Fallback for browsers that don't support View Transitions:
if (!document.startViewTransition) {
displayNewImage()
return
}

// With View Transitions:
const transition = document.startViewTransition(() => displayNewImage())
}

Transition Reference

CSS Animation

Animation Property

animation formal syntax:

  • animation-name.
  • animation-duration.
  • animation-delay: 支持负值.
  • animation-timing-function: <easing-function>.
  • animation-iteration-count:
    • infinite | <number> 执行次数.
    • 支持 0 与小数.
    • 不支持负值.
  • animation-direction:
    • normal: 0%->100% 方向.
    • reverse: 100%->0% 方向.
    • alternate/alternate-reverse: 不断交替方向.
  • animation-fill-mode: forwards/backwards/both.
  • animation-play-state: paused/running.
@media only screen and (prefers-reduced-motion: reduce) {
.element {
animation: none;
}
}

.element {
animation: name duration timing-function delay iteration-count direction;
}

Animation Fill Mode

animation-fill-mode:

  • forwards: 动画结束后, 应用动画最后一帧属性值.
  • backwards: 动画开始前, 应用动画第一帧属性值.
  • both: 同时应用上述两种效果.
animation-directionanimation-iteration-countlast keyframe
normaleven or odd100%
reverseeven or odd0%
alternateeven0%
alternateodd100%
alternate-reverseeven100%
alternate-reverseodd0%
normal/alternate00%
reverse/alternate-reverse0100%
animation-directionfirst keyframe
normal/alternate0%
reverse/alternate-reverse100%

Animation Play State

利用 animation-paly-state 与 JavaScript 添加 .animate 类控制动画开始和停止.

div {
animation-play-state: paused;
}

:checked ~ div {
animation-play-state: running;
}
@media only screen and (prefers-reduced-motion: reduce) {
.to-animate {
animation: none;
}
}

.to-animate {
animation: animationName 1.5s linear;
animation-play-state: paused;
animation-iteration-count: infinite;
}

.animate {
animation-iteration-count: running;
}
element.classList.add('animate')
setTimeout(() => element.classList.remove('animate'), duration)

Offset Animation

offset, animating an element along a defined path:

.path {
/* Offset position */
offset: auto;
offset: 10px 30px;
offset: none;

/* Offset path */
/* stylelint-disable-next-line function-no-unknown */
offset: ray(45deg closest-side);
offset: url('arc.svg');
offset: path('M 100 100 L 300 100 L 200 300 z');

/* Offset path with distance and/or rotation */
offset: url('circle.svg') 100px;
offset: url('circle.svg') 40%;
offset: url('circle.svg') 30deg;
offset: url('circle.svg') 50px 20deg;

/* Including offset anchor */
/* stylelint-disable-next-line function-no-unknown */
offset: ray(45deg closest-side) / 40px 20px;
offset: url('arc.svg') 2cm / 0.5cm 3cm;
offset: url('arc.svg') 30deg / 50px 100px;
}

Animation FLIP Pattern

  • First: 初始状态.
  • Last: 动画结束状态.
  • Invert: last 至 first 的 transform 属性.
  • Play: transition: transform .2s linear.
@media only screen and (prefers-reduced-motion: reduce) {
.scale-up {
transition: none;
}
}

/* first: scale(1), last: scale(1.2) */
.scale-up {
transition: transform 0.2s linear;
transform: scale(0.8);
}

.scale-up:hover,
.scale-up:focus {
transform: none;
}

Animation Bounce Cache Pattern

  • First -100.
  • Then +5/+20.
  • Finally 0.
  • 切换动画时, 需要先把之前的动画清除: 防止出现闪烁 Bug.

Animation Helper

  • opacity.
  • overflow: hidden.
  • transform: scale/translate.
  • transition.
  • animation-delay.
  • width/height
  • max-width/max-height.
  • margin.
  • border-*.
  • background.
  • background-position.
  • background with multiple gradient.
  • Single box-shadow
  • Multiple box-shadow.
  • *-clip-*.
  • mask-*.
  • filter.
  • backdrop-filter.
  • Pseudo element (::before/::after).
  • Pseudo class (:hover/:focus/:target).
  • Changing top/right/bottom/left of pseudo element can change animation start point: e.g bottom: 0, right: 0 change width/height from 0 to 100%, size animation will start from bottom-right corner.
.animation-container {
z-index: -1;
overflow: hidden;
}
/* 直接动画 */
.div {
animation-name: name;
animation-duration: 1s;
animation-timing-function: cubic-bezier(0.42, 0, 0.58, 1);
animation-delay: 0.5s;
}

/* hover 后再播放动画, 高级化 transform + transition */
.div:hover,
.div:focus {
animation-name: name;
animation-duration: 1s;
animation-timing-function: cubic-bezier(0.42, 0, 0.58, 1);
animation-delay: 0.5s;
}

Animation API

DOM events:

  • animationiteration: triggered after each animation iteration.
  • animationend: triggered after an animation completes.
  • animationstart: triggered at the start of an animation.

GreenSock Library

TweenMax

TweenMax.fromTo(element, 1, { x: 0 }, { x: 100 })

TimelineMax

const tl = new TimelineMax()
tl.staggerFrom(
[
'#Cap_1 > g > path:nth-child(1)',
'#Cap_1 > circle:nth-child(7)',
'#Cap_1 > path:nth-child(6)',
'#Cap_1 > circle:nth-child(5)',
],
1,
{
scaleY: 0,
scaleX: 0,
transformOrigin: 'center',
ease: Bounce.easeOut,
stagger: 0.2,
}
)

Animation Reference