浏览器渲染原理

INFO

这部分内容是【渡一教育 - WEB前端大师课 - 浏览器渲染原理】的学习笔记。

啥叫渲染 —— Render

将 html 字符串变为屏幕上的像素信息，这个过程叫渲染。

// 示意
function render(html) {
    return pixels
}

面试题

浏览器输入 url 到显示页面期间，都做了什么事。

网络
网络进程中的网络线程拿到 html。
生成渲染任务，放入消息队列。
渲染
渲染主线程在消息队列中拿到渲染任务，进行渲染

alt text

面试题

相关面试题：浏览器是如何渲染页面的？

渲染时间点

alt text

每个阶段都有输入和输出，上一个阶段的输入会变成下个阶段的输出。

输入 HTML 字符串

解析 HTML
样式计算
布局
分层
绘制
分块
光栅化
画

得到像素信息

面试题

相关面试题：浏览器是如何渲染页面的 —— 渲染时间点

1. 解析 HTML —— Parse HTML

总的来说，就是将 HTML 转化为两棵树：DOM 树和 CSSOM 树。

alt text

DOM 树

alt text

> document
< #document (https://www.baidu.com)
> typeof document
< 'object'
> console.dir(document)
< #document
f: （…）
jQuery110205025669316202075: 9
location: Location {ancestorOrigins: DOMStringList, href: 'https://www.baidu.com/', origin: 'https://www.baidu.com', protocol: 'https:', host: 'www.baidu.com', …}
...

DOM 树是在 C++ 中的对象，DOM 树的 JS 对象是为了能方便地方位 C++ 中的 DOM 树。

CSSOM 树

alt text

HTML 中有哪些样式
- 内部样式表 <style>
- 外部样式表 <link...>
- 内联样式表 <div style...
- 浏览器默认样式表

p 元素、div 元素独占一行，等默认行为，是因为浏览器默认样式。

除了浏览器默认样式，JS 都能操作。平时操作最多的是内联样式。dom.style。

另外两个样式可以用下面的方式操作。

> document.styleSheets[0]
CSSStyleSheet {
    ownerRule: null, 
    type: 'text/css', 
    href: 'https://pss.bdstatic.com/r/www/static/font/cosmic/pc/cos-icon_99f656e.css', 
    ownerNode: link, 
    parentStyleSheet: null, …}
    cssRules: （…）
    disabled: false
    href: "https://pss.bdstatic.com/r/www/static/font/cosmic/pc/cos-icon_99f656e.css"
    media: MediaList {length: 0, mediaText: ''}
    ownerNode: 
    linkownerRule: null
    parentStyleSheet: null
    rules: （…）
    title: null
    type: "text/css"
    [[Prototype]]: CSSStyleSheet
}
> document.styleSheets
< StyleSheetList {
    0: CSSStyleSheet,
    1: CSSStyleSheet,
    2: CSSStyleSheet,
    3: CSSStyleSheet,
    ...
    length: 21
}
> document.styleSheets[1].cssRules
< 0: CSSStyleRule {selectorText: '#form .bdsug', style: CSSStyleDeclaration, styleMap: StylePropertyMap, cssRules: CSSRuleList, type: 1, …}
1: CSSStyleRule {selectorText: '.bdsug', style: CSSStyleDeclaration, styleMap: StylePropertyMap, cssRules: CSSRuleList, type: 1, …}
2: CSSStyleRule {selectorText: '.bdsug li', style: CSSStyleDeclaration, styleMap: StylePropertyMap, cssRules: CSSRuleList, type: 1, …}
3: CSSStyleRule {selectorText: '.bdsug li.bdsug-s', style: CSSStyleDeclaration, styleMap: StylePropertyMap, cssRules: CSSRuleList, type: 1, …}
4: CSSStyleRule {selectorText: '.bdsug-store span, .bdsug-store b', style: CSSStyleDeclaration, styleMap: StylePropertyMap, cssRules: CSSRuleList, type: 1, …}
5: CSSStyleRule {selectorText: '.bdsug-store-del', style: CSSStyleDeclaration, styleMap: StylePropertyMap, cssRules: CSSRuleList, type: 1, …}
...

使用这种方式甚至可以添加样式。

> document.styleSheets[1].addRule('div', 'border: 1px red solid !important')
< -1

alt text

这种做法的好处是不会在标签中体现，而是直接操作样式表。

为什么要转换为 DOM 和 CSSOM 树
- 为了后续不需要再操作字符串
- 为 JS 操作 DOM 和 CSSOM 提供支持

HTML 过程解析过程中遇到 CSS 怎么办

预解析线程快速浏览文档，遇到 CSS 后交给网络进程去下载，下载完成后交给主线程处理。

CSS 不会阻塞主线程。

alt text

面试题

HTML 过程解析过程中遇到 CSS 怎么办? 解析 HTML。

HTML 解析过程中遇到 JS 怎么办

主线程暂停一切，等待下载完成后，将 JS 脚本放到 v8 引擎中执行完毕。

alt text

为什么会这样

因为 JS 可能会修改当前 DOM 树。

面试题

HTML 解析过程中遇到 JS 怎么办? 解析 HTML。

思考

为什么 JS 没有生成树？
- JS 执行一遍就完事了，不需要。
- DOM 和 CSSOM 都是给 JS 用的。

2. 样式计算 —— Recalculate Style

将计算后的 CSS 属性放到 DOM 树上，得到带有最终样式的 DOM 树。

alt text

CSS 属性值的计算过程就是在这一步发生的。

相关内容 —— CSS 属性值的计算过程

层叠
继承
...

相关内容 —— 视觉格式化模型

盒模型
包含块
流式布局
浮动布局
BFC
...

最终样式

就是计算后的样式（Computed Style），每个元素的所有的 CSS 属性都必须有值。

在【浏览器 F12 - 元素 - 点击一个元素 - 计算样式（Computed） - 勾选全部显示（Show all）】中可以看到。

alt text

在计算过程中，有的值会变化。例如在样式表中设置的 em，计算后都会变成 px。例如我们在页面上为一个元素设置相对大小的字号。

alt text

我们可以在 Computed 中看到已经计算为了绝对尺寸。

alt text

获取计算后的样式

隐藏点击显示

> getComputedStyle

// 有点多，结果给隐藏了，点右面看

> temp1
< <a href="https://haokan.baidu.com/?sfrom=baidu-top" target="_blank" class="mnav c-font-normal c-color-t" style="font-size: 2em;">视频</a>
> getComputedStyle(temp1)
< {
    "0": "accent-color",
    "1": "align-content",
    "2": "align-items",
    "3": "align-self",
    "4": "alignment-baseline",
    "5": "anchor-name",
    "6": "animation-composition",
    "7": "animation-delay",
    "8": "animation-direction",
    "9": "animation-duration",
    "10": "animation-fill-mode",
    "11": "animation-iteration-count",
    "12": "animation-name",
    "13": "animation-play-state",
    "14": "animation-range-end",
    "15": "animation-range-start",
    "16": "animation-timeline",
    "17": "animation-timing-function",
    "18": "app-region",
    "19": "appearance",
    "20": "backdrop-filter",
    "21": "backface-visibility",
    "22": "background-attachment",
    "23": "background-blend-mode",
    "24": "background-clip",
    "25": "background-color",
    "26": "background-image",
    "27": "background-origin",
    "28": "background-position",
    "29": "background-repeat",
    "30": "background-size",
    "31": "baseline-shift",
    "32": "baseline-source",
    "33": "block-size",
    "34": "border-block-end-color",
    "35": "border-block-end-style",
    "36": "border-block-end-width",
    "37": "border-block-start-color",
    "38": "border-block-start-style",
    "39": "border-block-start-width",
    "40": "border-bottom-color",
    "41": "border-bottom-left-radius",
    "42": "border-bottom-right-radius",
    "43": "border-bottom-style",
    "44": "border-bottom-width",
    "45": "border-collapse",
    "46": "border-end-end-radius",
    "47": "border-end-start-radius",
    "48": "border-image-outset",
    "49": "border-image-repeat",
    "50": "border-image-slice",
    "51": "border-image-source",
    "52": "border-image-width",
    "53": "border-inline-end-color",
    "54": "border-inline-end-style",
    "55": "border-inline-end-width",
    "56": "border-inline-start-color",
    "57": "border-inline-start-style",
    "58": "border-inline-start-width",
    "59": "border-left-color",
    "60": "border-left-style",
    "61": "border-left-width",
    "62": "border-right-color",
    "63": "border-right-style",
    "64": "border-right-width",
    "65": "border-start-end-radius",
    "66": "border-start-start-radius",
    "67": "border-top-color",
    "68": "border-top-left-radius",
    "69": "border-top-right-radius",
    "70": "border-top-style",
    "71": "border-top-width",
    "72": "bottom",
    "73": "box-shadow",
    "74": "box-sizing",
    "75": "break-after",
    "76": "break-before",
    "77": "break-inside",
    "78": "buffered-rendering",
    "79": "caption-side",
    "80": "caret-color",
    "81": "clear",
    "82": "clip",
    "83": "clip-path",
    "84": "clip-rule",
    "85": "color",
    "86": "color-interpolation",
    "87": "color-interpolation-filters",
    "88": "color-rendering",
    "89": "column-count",
    "90": "column-gap",
    "91": "column-rule-color",
    "92": "column-rule-style",
    "93": "column-rule-width",
    "94": "column-span",
    "95": "column-width",
    "96": "contain-intrinsic-block-size",
    "97": "contain-intrinsic-height",
    "98": "contain-intrinsic-inline-size",
    "99": "contain-intrinsic-size",
    "100": "contain-intrinsic-width",
    "101": "container-name",
    "102": "container-type",
    "103": "content",
    "104": "cursor",
    "105": "cx",
    "106": "cy",
    "107": "d",
    "108": "direction",
    "109": "display",
    "110": "dominant-baseline",
    "111": "empty-cells",
    "112": "field-sizing",
    "113": "fill",
    "114": "fill-opacity",
    "115": "fill-rule",
    "116": "filter",
    "117": "flex-basis",
    "118": "flex-direction",
    "119": "flex-grow",
    "120": "flex-shrink",
    "121": "flex-wrap",
    "122": "float",
    "123": "flood-color",
    "124": "flood-opacity",
    "125": "font-family",
    "126": "font-kerning",
    "127": "font-optical-sizing",
    "128": "font-palette",
    "129": "font-size",
    "130": "font-size-adjust",
    "131": "font-stretch",
    "132": "font-style",
    "133": "font-synthesis-small-caps",
    "134": "font-synthesis-style",
    "135": "font-synthesis-weight",
    "136": "font-variant",
    "137": "font-variant-alternates",
    "138": "font-variant-caps",
    "139": "font-variant-east-asian",
    "140": "font-variant-ligatures",
    "141": "font-variant-numeric",
    "142": "font-variant-position",
    "143": "font-weight",
    "144": "grid-auto-columns",
    "145": "grid-auto-flow",
    "146": "grid-auto-rows",
    "147": "grid-column-end",
    "148": "grid-column-start",
    "149": "grid-row-end",
    "150": "grid-row-start",
    "151": "grid-template-areas",
    "152": "grid-template-columns",
    "153": "grid-template-rows",
    "154": "height",
    "155": "hyphenate-character",
    "156": "hyphenate-limit-chars",
    "157": "hyphens",
    "158": "image-orientation",
    "159": "image-rendering",
    "160": "initial-letter",
    "161": "inline-size",
    "162": "inset-area",
    "163": "inset-block-end",
    "164": "inset-block-start",
    "165": "inset-inline-end",
    "166": "inset-inline-start",
    "167": "isolation",
    "168": "justify-content",
    "169": "justify-items",
    "170": "justify-self",
    "171": "left",
    "172": "letter-spacing",
    "173": "lighting-color",
    "174": "line-break",
    "175": "line-height",
    "176": "list-style-image",
    "177": "list-style-position",
    "178": "list-style-type",
    "179": "margin-block-end",
    "180": "margin-block-start",
    "181": "margin-bottom",
    "182": "margin-inline-end",
    "183": "margin-inline-start",
    "184": "margin-left",
    "185": "margin-right",
    "186": "margin-top",
    "187": "marker-end",
    "188": "marker-mid",
    "189": "marker-start",
    "190": "mask-clip",
    "191": "mask-composite",
    "192": "mask-image",
    "193": "mask-mode",
    "194": "mask-origin",
    "195": "mask-position",
    "196": "mask-repeat",
    "197": "mask-size",
    "198": "mask-type",
    "199": "math-depth",
    "200": "math-shift",
    "201": "math-style",
    "202": "max-block-size",
    "203": "max-height",
    "204": "max-inline-size",
    "205": "max-width",
    "206": "min-block-size",
    "207": "min-height",
    "208": "min-inline-size",
    "209": "min-width",
    "210": "mix-blend-mode",
    "211": "object-fit",
    "212": "object-position",
    "213": "object-view-box",
    "214": "offset-anchor",
    "215": "offset-distance",
    "216": "offset-path",
    "217": "offset-position",
    "218": "offset-rotate",
    "219": "opacity",
    "220": "order",
    "221": "orphans",
    "222": "outline-color",
    "223": "outline-offset",
    "224": "outline-style",
    "225": "outline-width",
    "226": "overflow-anchor",
    "227": "overflow-clip-margin",
    "228": "overflow-wrap",
    "229": "overflow-x",
    "230": "overflow-y",
    "231": "overlay",
    "232": "overscroll-behavior-block",
    "233": "overscroll-behavior-inline",
    "234": "padding-block-end",
    "235": "padding-block-start",
    "236": "padding-bottom",
    "237": "padding-inline-end",
    "238": "padding-inline-start",
    "239": "padding-left",
    "240": "padding-right",
    "241": "padding-top",
    "242": "paint-order",
    "243": "perspective",
    "244": "perspective-origin",
    "245": "pointer-events",
    "246": "position",
    "247": "position-anchor",
    "248": "position-try-fallbacks",
    "249": "position-try-order",
    "250": "position-visibility",
    "251": "r",
    "252": "resize",
    "253": "right",
    "254": "rotate",
    "255": "row-gap",
    "256": "ruby-align",
    "257": "ruby-position",
    "258": "rx",
    "259": "ry",
    "260": "scale",
    "261": "scroll-behavior",
    "262": "scroll-margin-block-end",
    "263": "scroll-margin-block-start",
    "264": "scroll-margin-inline-end",
    "265": "scroll-margin-inline-start",
    "266": "scroll-padding-block-end",
    "267": "scroll-padding-block-start",
    "268": "scroll-padding-inline-end",
    "269": "scroll-padding-inline-start",
    "270": "scroll-timeline-axis",
    "271": "scroll-timeline-name",
    "272": "scrollbar-color",
    "273": "scrollbar-gutter",
    "274": "scrollbar-width",
    "275": "shape-image-threshold",
    "276": "shape-margin",
    "277": "shape-outside",
    "278": "shape-rendering",
    "279": "speak",
    "280": "stop-color",
    "281": "stop-opacity",
    "282": "stroke",
    "283": "stroke-dasharray",
    "284": "stroke-dashoffset",
    "285": "stroke-linecap",
    "286": "stroke-linejoin",
    "287": "stroke-miterlimit",
    "288": "stroke-opacity",
    "289": "stroke-width",
    "290": "tab-size",
    "291": "table-layout",
    "292": "text-align",
    "293": "text-align-last",
    "294": "text-anchor",
    "295": "text-decoration",
    "296": "text-decoration-color",
    "297": "text-decoration-line",
    "298": "text-decoration-skip-ink",
    "299": "text-decoration-style",
    "300": "text-emphasis-color",
    "301": "text-emphasis-position",
    "302": "text-emphasis-style",
    "303": "text-indent",
    "304": "text-overflow",
    "305": "text-rendering",
    "306": "text-shadow",
    "307": "text-size-adjust",
    "308": "text-spacing-trim",
    "309": "text-transform",
    "310": "text-underline-position",
    "311": "text-wrap",
    "312": "timeline-scope",
    "313": "top",
    "314": "touch-action",
    "315": "transform",
    "316": "transform-origin",
    "317": "transform-style",
    "318": "transition-behavior",
    "319": "transition-delay",
    "320": "transition-duration",
    "321": "transition-property",
    "322": "transition-timing-function",
    "323": "translate",
    "324": "unicode-bidi",
    "325": "user-select",
    "326": "vector-effect",
    "327": "vertical-align",
    "328": "view-timeline-axis",
    "329": "view-timeline-inset",
    "330": "view-timeline-name",
    "331": "view-transition-class",
    "332": "view-transition-name",
    "333": "visibility",
    "334": "white-space-collapse",
    "335": "widows",
    "336": "width",
    "337": "will-change",
    "338": "word-break",
    "339": "word-spacing",
    "340": "writing-mode",
    "341": "x",
    "342": "y",
    "343": "z-index",
    "344": "zoom",
    "345": "-webkit-border-horizontal-spacing",
    "346": "-webkit-border-image",
    "347": "-webkit-border-vertical-spacing",
    "348": "-webkit-box-align",
    "349": "-webkit-box-decoration-break",
    "350": "-webkit-box-direction",
    "351": "-webkit-box-flex",
    "352": "-webkit-box-ordinal-group",
    "353": "-webkit-box-orient",
    "354": "-webkit-box-pack",
    "355": "-webkit-box-reflect",
    "356": "-webkit-font-smoothing",
    "357": "-webkit-line-break",
    "358": "-webkit-line-clamp",
    "359": "-webkit-locale",
    "360": "-webkit-mask-box-image",
    "361": "-webkit-mask-box-image-outset",
    "362": "-webkit-mask-box-image-repeat",
    "363": "-webkit-mask-box-image-slice",
    "364": "-webkit-mask-box-image-source",
    "365": "-webkit-mask-box-image-width",
    "366": "-webkit-print-color-adjust",
    "367": "-webkit-rtl-ordering",
    "368": "-webkit-tap-highlight-color",
    "369": "-webkit-text-combine",
    "370": "-webkit-text-decorations-in-effect",
    "371": "-webkit-text-fill-color",
    "372": "-webkit-text-orientation",
    "373": "-webkit-text-security",
    "374": "-webkit-text-stroke-color",
    "375": "-webkit-text-stroke-width",
    "376": "-webkit-user-drag",
    "377": "-webkit-user-modify",
    "378": "-webkit-writing-mode",
    "accentColor": "auto",
    "additiveSymbols": "",
    "alignContent": "normal",
    "alignItems": "normal",
    "alignSelf": "auto",
    "alignmentBaseline": "auto",
    "all": "",
    "anchorName": "none",
    "animation": "none 0s ease 0s 1 normal none running",
    "animationComposition": "replace",
    "animationDelay": "0s",
    "animationDirection": "normal",
    "animationDuration": "0s",
    "animationFillMode": "none",
    "animationIterationCount": "1",
    "animationName": "none",
    "animationPlayState": "running",
    "animationRange": "normal",
    "animationRangeEnd": "normal",
    "animationRangeStart": "normal",
    "animationTimeline": "auto",
    "animationTimingFunction": "ease",
    "appRegion": "none",
    "appearance": "none",
    "ascentOverride": "",
    "aspectRatio": "auto",
    "backdropFilter": "none",
    "backfaceVisibility": "visible",
    "background": "rgba(0, 0, 0, 0) none repeat scroll 0% 0% / auto padding-box border-box",
    "backgroundAttachment": "scroll",
    "backgroundBlendMode": "normal",
    "backgroundClip": "border-box",
    "backgroundColor": "rgba(0, 0, 0, 0)",
    "backgroundImage": "none",
    "backgroundOrigin": "padding-box",
    "backgroundPosition": "0% 0%",
    "backgroundPositionX": "0%",
    "backgroundPositionY": "0%",
    "backgroundRepeat": "repeat",
    "backgroundSize": "auto",
    "basePalette": "",
    "baselineShift": "0px",
    "baselineSource": "auto",
    "blockSize": "23px",
    "border": "0px none rgb(34, 34, 34)",
    "borderBlock": "0px none rgb(34, 34, 34)",
    "borderBlockColor": "rgb(34, 34, 34)",
    "borderBlockEnd": "0px none rgb(34, 34, 34)",
    "borderBlockEndColor": "rgb(34, 34, 34)",
    "borderBlockEndStyle": "none",
    "borderBlockEndWidth": "0px",
    "borderBlockStart": "0px none rgb(34, 34, 34)",
    "borderBlockStartColor": "rgb(34, 34, 34)",
    "borderBlockStartStyle": "none",
    "borderBlockStartWidth": "0px",
    "borderBlockStyle": "none",
    "borderBlockWidth": "0px",
    "borderBottom": "0px none rgb(34, 34, 34)",
    "borderBottomColor": "rgb(34, 34, 34)",
    "borderBottomLeftRadius": "0px",
    "borderBottomRightRadius": "0px",
    "borderBottomStyle": "none",
    "borderBottomWidth": "0px",
    "borderCollapse": "separate",
    "borderColor": "rgb(34, 34, 34)",
    "borderEndEndRadius": "0px",
    "borderEndStartRadius": "0px",
    "borderImage": "none",
    "borderImageOutset": "0",
    "borderImageRepeat": "stretch",
    "borderImageSlice": "100%",
    "borderImageSource": "none",
    "borderImageWidth": "1",
    "borderInline": "0px none rgb(34, 34, 34)",
    "borderInlineColor": "rgb(34, 34, 34)",
    "borderInlineEnd": "0px none rgb(34, 34, 34)",
    "borderInlineEndColor": "rgb(34, 34, 34)",
    "borderInlineEndStyle": "none",
    "borderInlineEndWidth": "0px",
    "borderInlineStart": "0px none rgb(34, 34, 34)",
    "borderInlineStartColor": "rgb(34, 34, 34)",
    "borderInlineStartStyle": "none",
    "borderInlineStartWidth": "0px",
    "borderInlineStyle": "none",
    "borderInlineWidth": "0px",
    "borderLeft": "0px none rgb(34, 34, 34)",
    "borderLeftColor": "rgb(34, 34, 34)",
    "borderLeftStyle": "none",
    "borderLeftWidth": "0px",
    "borderRadius": "0px",
    "borderRight": "0px none rgb(34, 34, 34)",
    "borderRightColor": "rgb(34, 34, 34)",
    "borderRightStyle": "none",
    "borderRightWidth": "0px",
    "borderSpacing": "0px 0px",
    "borderStartEndRadius": "0px",
    "borderStartStartRadius": "0px",
    "borderStyle": "none",
    "borderTop": "0px none rgb(34, 34, 34)",
    "borderTopColor": "rgb(34, 34, 34)",
    "borderTopLeftRadius": "0px",
    "borderTopRightRadius": "0px",
    "borderTopStyle": "none",
    "borderTopWidth": "0px",
    "borderWidth": "0px",
    "bottom": "0px",
    "boxShadow": "none",
    "boxSizing": "content-box",
    "breakAfter": "auto",
    "breakBefore": "auto",
    "breakInside": "auto",
    "bufferedRendering": "auto",
    "captionSide": "top",
    "caretColor": "rgb(34, 34, 34)",
    "clear": "none",
    "clip": "auto",
    "clipPath": "none",
    "clipRule": "nonzero",
    "color": "rgb(34, 34, 34)",
    "colorInterpolation": "srgb",
    "colorInterpolationFilters": "linearrgb",
    "colorRendering": "auto",
    "colorScheme": "normal",
    "columnCount": "auto",
    "columnFill": "balance",
    "columnGap": "normal",
    "columnRule": "0px none rgb(34, 34, 34)",
    "columnRuleColor": "rgb(34, 34, 34)",
    "columnRuleStyle": "none",
    "columnRuleWidth": "0px",
    "columnSpan": "none",
    "columnWidth": "auto",
    "columns": "auto auto",
    "contain": "none",
    "containIntrinsicBlockSize": "none",
    "containIntrinsicHeight": "none",
    "containIntrinsicInlineSize": "none",
    "containIntrinsicSize": "none",
    "containIntrinsicWidth": "none",
    "container": "none",
    "containerName": "none",
    "containerType": "normal",
    "content": "normal",
    "contentVisibility": "visible",
    "counterIncrement": "none",
    "counterReset": "none",
    "counterSet": "none",
    "cursor": "pointer",
    "cx": "0px",
    "cy": "0px",
    "d": "none",
    "descentOverride": "",
    "direction": "ltr",
    "display": "inline-block",
    "dominantBaseline": "auto",
    "emptyCells": "show",
    "fallback": "",
    "fieldSizing": "fixed",
    "fill": "rgb(0, 0, 0)",
    "fillOpacity": "1",
    "fillRule": "nonzero",
    "filter": "none",
    "flex": "0 1 auto",
    "flexBasis": "auto",
    "flexDirection": "row",
    "flexFlow": "row nowrap",
    "flexGrow": "0",
    "flexShrink": "1",
    "flexWrap": "nowrap",
    "float": "none",
    "floodColor": "rgb(0, 0, 0)",
    "floodOpacity": "1",
    "font": "24px / 23px Arial, sans-serif",
    "fontDisplay": "",
    "fontFamily": "Arial, sans-serif",
    "fontFeatureSettings": "normal",
    "fontKerning": "auto",
    "fontOpticalSizing": "auto",
    "fontPalette": "normal",
    "fontSize": "24px",
    "fontSizeAdjust": "none",
    "fontStretch": "100%",
    "fontStyle": "normal",
    "fontSynthesis": "weight style small-caps",
    "fontSynthesisSmallCaps": "auto",
    "fontSynthesisStyle": "auto",
    "fontSynthesisWeight": "auto",
    "fontVariant": "normal",
    "fontVariantAlternates": "normal",
    "fontVariantCaps": "normal",
    "fontVariantEastAsian": "normal",
    "fontVariantLigatures": "normal",
    "fontVariantNumeric": "normal",
    "fontVariantPosition": "normal",
    "fontVariationSettings": "normal",
    "fontWeight": "400",
    "forcedColorAdjust": "auto",
    "gap": "normal",
    "grid": "none / none / none / row / auto / auto",
    "gridArea": "auto",
    "gridAutoColumns": "auto",
    "gridAutoFlow": "row",
    "gridAutoRows": "auto",
    "gridColumn": "auto",
    "gridColumnEnd": "auto",
    "gridColumnGap": "normal",
    "gridColumnStart": "auto",
    "gridGap": "normal",
    "gridRow": "auto",
    "gridRowEnd": "auto",
    "gridRowGap": "normal",
    "gridRowStart": "auto",
    "gridTemplate": "none",
    "gridTemplateAreas": "none",
    "gridTemplateColumns": "none",
    "gridTemplateRows": "none",
    "height": "23px",
    "hyphenateCharacter": "auto",
    "hyphenateLimitChars": "auto",
    "hyphens": "manual",
    "imageOrientation": "from-image",
    "imageRendering": "auto",
    "inherits": "",
    "initialLetter": "normal",
    "initialValue": "",
    "inlineSize": "48px",
    "inset": "0px",
    "insetArea": "none",
    "insetBlock": "0px",
    "insetBlockEnd": "0px",
    "insetBlockStart": "0px",
    "insetInline": "0px",
    "insetInlineEnd": "0px",
    "insetInlineStart": "0px",
    "isolation": "auto",
    "justifyContent": "normal",
    "justifyItems": "normal",
    "justifySelf": "auto",
    "left": "0px",
    "letterSpacing": "normal",
    "lightingColor": "rgb(255, 255, 255)",
    "lineBreak": "auto",
    "lineGapOverride": "",
    "lineHeight": "23px",
    "listStyle": "outside none disc",
    "listStyleImage": "none",
    "listStylePosition": "outside",
    "listStyleType": "disc",
    "margin": "19px 24px 0px 0px",
    "marginBlock": "19px 0px",
    "marginBlockEnd": "0px",
    "marginBlockStart": "19px",
    "marginBottom": "0px",
    "marginInline": "0px 24px",
    "marginInlineEnd": "24px",
    "marginInlineStart": "0px",
    "marginLeft": "0px",
    "marginRight": "24px",
    "marginTop": "19px",
    "marker": "none",
    "markerEnd": "none",
    "markerMid": "none",
    "markerStart": "none",
    "mask": "none",
    "maskClip": "border-box",
    "maskComposite": "add",
    "maskImage": "none",
    "maskMode": "match-source",
    "maskOrigin": "border-box",
    "maskPosition": "0% 0%",
    "maskRepeat": "repeat",
    "maskSize": "auto",
    "maskType": "luminance",
    "mathDepth": "0",
    "mathShift": "normal",
    "mathStyle": "normal",
    "maxBlockSize": "none",
    "maxHeight": "none",
    "maxInlineSize": "none",
    "maxWidth": "none",
    "minBlockSize": "0px",
    "minHeight": "0px",
    "minInlineSize": "0px",
    "minWidth": "0px",
    "mixBlendMode": "normal",
    "navigation": "",
    "negative": "",
    "objectFit": "fill",
    "objectPosition": "50% 50%",
    "objectViewBox": "none",
    "offset": "none 0px auto 0deg",
    "offsetAnchor": "auto",
    "offsetDistance": "0px",
    "offsetPath": "none",
    "offsetPosition": "normal",
    "offsetRotate": "auto 0deg",
    "opacity": "1",
    "order": "0",
    "orphans": "2",
    "outline": "rgb(34, 34, 34) none 0px",
    "outlineColor": "rgb(34, 34, 34)",
    "outlineOffset": "0px",
    "outlineStyle": "none",
    "outlineWidth": "0px",
    "overflow": "visible",
    "overflowAnchor": "auto",
    "overflowClipMargin": "0px",
    "overflowWrap": "normal",
    "overflowX": "visible",
    "overflowY": "visible",
    "overlay": "none",
    "overrideColors": "",
    "overscrollBehavior": "auto",
    "overscrollBehaviorBlock": "auto",
    "overscrollBehaviorInline": "auto",
    "overscrollBehaviorX": "auto",
    "overscrollBehaviorY": "auto",
    "pad": "",
    "padding": "0px",
    "paddingBlock": "0px",
    "paddingBlockEnd": "0px",
    "paddingBlockStart": "0px",
    "paddingBottom": "0px",
    "paddingInline": "0px",
    "paddingInlineEnd": "0px",
    "paddingInlineStart": "0px",
    "paddingLeft": "0px",
    "paddingRight": "0px",
    "paddingTop": "0px",
    "page": "auto",
    "pageBreakAfter": "auto",
    "pageBreakBefore": "auto",
    "pageBreakInside": "auto",
    "pageOrientation": "",
    "paintOrder": "normal",
    "perspective": "none",
    "perspectiveOrigin": "24px 11.5px",
    "placeContent": "normal",
    "placeItems": "normal",
    "placeSelf": "auto",
    "pointerEvents": "auto",
    "position": "relative",
    "positionAnchor": "auto",
    "positionTry": "none",
    "positionTryFallbacks": "none",
    "positionTryOrder": "normal",
    "positionVisibility": "always",
    "prefix": "",
    "quotes": "auto",
    "r": "0px",
    "range": "",
    "resize": "none",
    "right": "0px",
    "rotate": "none",
    "rowGap": "normal",
    "rubyAlign": "space-around",
    "rubyPosition": "over",
    "rx": "auto",
    "ry": "auto",
    "scale": "none",
    "scrollBehavior": "auto",
    "scrollMargin": "0px",
    "scrollMarginBlock": "0px",
    "scrollMarginBlockEnd": "0px",
    "scrollMarginBlockStart": "0px",
    "scrollMarginBottom": "0px",
    "scrollMarginInline": "0px",
    "scrollMarginInlineEnd": "0px",
    "scrollMarginInlineStart": "0px",
    "scrollMarginLeft": "0px",
    "scrollMarginRight": "0px",
    "scrollMarginTop": "0px",
    "scrollPadding": "auto",
    "scrollPaddingBlock": "auto",
    "scrollPaddingBlockEnd": "auto",
    "scrollPaddingBlockStart": "auto",
    "scrollPaddingBottom": "auto",
    "scrollPaddingInline": "auto",
    "scrollPaddingInlineEnd": "auto",
    "scrollPaddingInlineStart": "auto",
    "scrollPaddingLeft": "auto",
    "scrollPaddingRight": "auto",
    "scrollPaddingTop": "auto",
    "scrollSnapAlign": "none",
    "scrollSnapStop": "normal",
    "scrollSnapType": "none",
    "scrollTimeline": "none",
    "scrollTimelineAxis": "block",
    "scrollTimelineName": "none",
    "scrollbarColor": "auto",
    "scrollbarGutter": "auto",
    "scrollbarWidth": "auto",
    "shapeImageThreshold": "0",
    "shapeMargin": "0px",
    "shapeOutside": "none",
    "shapeRendering": "auto",
    "size": "",
    "sizeAdjust": "",
    "speak": "normal",
    "speakAs": "",
    "src": "",
    "stopColor": "rgb(0, 0, 0)",
    "stopOpacity": "1",
    "stroke": "none",
    "strokeDasharray": "none",
    "strokeDashoffset": "0px",
    "strokeLinecap": "butt",
    "strokeLinejoin": "miter",
    "strokeMiterlimit": "4",
    "strokeOpacity": "1",
    "strokeWidth": "1px",
    "suffix": "",
    "symbols": "",
    "syntax": "",
    "system": "",
    "tabSize": "8",
    "tableLayout": "auto",
    "textAlign": "center",
    "textAlignLast": "auto",
    "textAnchor": "start",
    "textCombineUpright": "none",
    "textDecoration": "none solid rgb(34, 34, 34)",
    "textDecorationColor": "rgb(34, 34, 34)",
    "textDecorationLine": "none",
    "textDecorationSkipInk": "auto",
    "textDecorationStyle": "solid",
    "textDecorationThickness": "auto",
    "textEmphasis": "none rgb(34, 34, 34)",
    "textEmphasisColor": "rgb(34, 34, 34)",
    "textEmphasisPosition": "over",
    "textEmphasisStyle": "none",
    "textIndent": "0px",
    "textOrientation": "mixed",
    "textOverflow": "clip",
    "textRendering": "auto",
    "textShadow": "none",
    "textSizeAdjust": "auto",
    "textSpacingTrim": "normal",
    "textTransform": "none",
    "textUnderlineOffset": "auto",
    "textUnderlinePosition": "auto",
    "textWrap": "wrap",
    "timelineScope": "none",
    "top": "0px",
    "touchAction": "auto",
    "transform": "none",
    "transformBox": "view-box",
    "transformOrigin": "24px 11.5px",
    "transformStyle": "flat",
    "transition": "all",
    "transitionBehavior": "normal",
    "transitionDelay": "0s",
    "transitionDuration": "0s",
    "transitionProperty": "all",
    "transitionTimingFunction": "ease",
    "translate": "none",
    "types": "",
    "unicodeBidi": "normal",
    "unicodeRange": "",
    "userSelect": "auto",
    "vectorEffect": "none",
    "verticalAlign": "baseline",
    "viewTimeline": "none",
    "viewTimelineAxis": "block",
    "viewTimelineInset": "auto",
    "viewTimelineName": "none",
    "viewTransitionClass": "none",
    "viewTransitionName": "none",
    "visibility": "visible",
    "webkitAlignContent": "normal",
    "webkitAlignItems": "normal",
    "webkitAlignSelf": "auto",
    "webkitAnimation": "none 0s ease 0s 1 normal none running",
    "webkitAnimationDelay": "0s",
    "webkitAnimationDirection": "normal",
    "webkitAnimationDuration": "0s",
    "webkitAnimationFillMode": "none",
    "webkitAnimationIterationCount": "1",
    "webkitAnimationName": "none",
    "webkitAnimationPlayState": "running",
    "webkitAnimationTimingFunction": "ease",
    "webkitAppRegion": "none",
    "webkitAppearance": "none",
    "webkitBackfaceVisibility": "visible",
    "webkitBackgroundClip": "border-box",
    "webkitBackgroundOrigin": "padding-box",
    "webkitBackgroundSize": "auto",
    "webkitBorderAfter": "0px none rgb(34, 34, 34)",
    "webkitBorderAfterColor": "rgb(34, 34, 34)",
    "webkitBorderAfterStyle": "none",
    "webkitBorderAfterWidth": "0px",
    "webkitBorderBefore": "0px none rgb(34, 34, 34)",
    "webkitBorderBeforeColor": "rgb(34, 34, 34)",
    "webkitBorderBeforeStyle": "none",
    "webkitBorderBeforeWidth": "0px",
    "webkitBorderBottomLeftRadius": "0px",
    "webkitBorderBottomRightRadius": "0px",
    "webkitBorderEnd": "0px none rgb(34, 34, 34)",
    "webkitBorderEndColor": "rgb(34, 34, 34)",
    "webkitBorderEndStyle": "none",
    "webkitBorderEndWidth": "0px",
    "webkitBorderHorizontalSpacing": "0px",
    "webkitBorderImage": "none",
    "webkitBorderRadius": "0px",
    "webkitBorderStart": "0px none rgb(34, 34, 34)",
    "webkitBorderStartColor": "rgb(34, 34, 34)",
    "webkitBorderStartStyle": "none",
    "webkitBorderStartWidth": "0px",
    "webkitBorderTopLeftRadius": "0px",
    "webkitBorderTopRightRadius": "0px",
    "webkitBorderVerticalSpacing": "0px",
    "webkitBoxAlign": "stretch",
    "webkitBoxDecorationBreak": "slice",
    "webkitBoxDirection": "normal",
    "webkitBoxFlex": "0",
    "webkitBoxOrdinalGroup": "1",
    "webkitBoxOrient": "horizontal",
    "webkitBoxPack": "start",
    "webkitBoxReflect": "none",
    "webkitBoxShadow": "none",
    "webkitBoxSizing": "content-box",
    "webkitClipPath": "none",
    "webkitColumnBreakAfter": "auto",
    "webkitColumnBreakBefore": "auto",
    "webkitColumnBreakInside": "auto",
    "webkitColumnCount": "auto",
    "webkitColumnGap": "normal",
    "webkitColumnRule": "0px none rgb(34, 34, 34)",
    "webkitColumnRuleColor": "rgb(34, 34, 34)",
    "webkitColumnRuleStyle": "none",
    "webkitColumnRuleWidth": "0px",
    "webkitColumnSpan": "none",
    "webkitColumnWidth": "auto",
    "webkitColumns": "auto auto",
    "webkitFilter": "none",
    "webkitFlex": "0 1 auto",
    "webkitFlexBasis": "auto",
    "webkitFlexDirection": "row",
    "webkitFlexFlow": "row nowrap",
    "webkitFlexGrow": "0",
    "webkitFlexShrink": "1",
    "webkitFlexWrap": "nowrap",
    "webkitFontFeatureSettings": "normal",
    "webkitFontSmoothing": "auto",
    "webkitHyphenateCharacter": "auto",
    "webkitJustifyContent": "normal",
    "webkitLineBreak": "auto",
    "webkitLineClamp": "none",
    "webkitLocale": "auto",
    "webkitLogicalHeight": "23px",
    "webkitLogicalWidth": "48px",
    "webkitMarginAfter": "0px",
    "webkitMarginBefore": "19px",
    "webkitMarginEnd": "24px",
    "webkitMarginStart": "0px",
    "webkitMask": "none",
    "webkitMaskBoxImage": "none",
    "webkitMaskBoxImageOutset": "0",
    "webkitMaskBoxImageRepeat": "stretch",
    "webkitMaskBoxImageSlice": "0 fill",
    "webkitMaskBoxImageSource": "none",
    "webkitMaskBoxImageWidth": "auto",
    "webkitMaskClip": "border-box",
    "webkitMaskComposite": "add",
    "webkitMaskImage": "none",
    "webkitMaskOrigin": "border-box",
    "webkitMaskPosition": "0% 0%",
    "webkitMaskPositionX": "0%",
    "webkitMaskPositionY": "0%",
    "webkitMaskRepeat": "repeat",
    "webkitMaskSize": "auto",
    "webkitMaxLogicalHeight": "none",
    "webkitMaxLogicalWidth": "none",
    "webkitMinLogicalHeight": "0px",
    "webkitMinLogicalWidth": "0px",
    "webkitOpacity": "1",
    "webkitOrder": "0",
    "webkitPaddingAfter": "0px",
    "webkitPaddingBefore": "0px",
    "webkitPaddingEnd": "0px",
    "webkitPaddingStart": "0px",
    "webkitPerspective": "none",
    "webkitPerspectiveOrigin": "24px 11.5px",
    "webkitPerspectiveOriginX": "",
    "webkitPerspectiveOriginY": "",
    "webkitPrintColorAdjust": "economy",
    "webkitRtlOrdering": "logical",
    "webkitRubyPosition": "before",
    "webkitShapeImageThreshold": "0",
    "webkitShapeMargin": "0px",
    "webkitShapeOutside": "none",
    "webkitTapHighlightColor": "rgba(0, 0, 0, 0.18)",
    "webkitTextCombine": "none",
    "webkitTextDecorationsInEffect": "none",
    "webkitTextEmphasis": "none rgb(34, 34, 34)",
    "webkitTextEmphasisColor": "rgb(34, 34, 34)",
    "webkitTextEmphasisPosition": "over",
    "webkitTextEmphasisStyle": "none",
    "webkitTextFillColor": "rgb(34, 34, 34)",
    "webkitTextOrientation": "vertical-right",
    "webkitTextSecurity": "none",
    "webkitTextSizeAdjust": "auto",
    "webkitTextStroke": "0px rgb(34, 34, 34)",
    "webkitTextStrokeColor": "rgb(34, 34, 34)",
    "webkitTextStrokeWidth": "0px",
    "webkitTransform": "none",
    "webkitTransformOrigin": "24px 11.5px",
    "webkitTransformOriginX": "",
    "webkitTransformOriginY": "",
    "webkitTransformOriginZ": "",
    "webkitTransformStyle": "flat",
    "webkitTransition": "all",
    "webkitTransitionDelay": "0s",
    "webkitTransitionDuration": "0s",
    "webkitTransitionProperty": "all",
    "webkitTransitionTimingFunction": "ease",
    "webkitUserDrag": "auto",
    "webkitUserModify": "read-only",
    "webkitUserSelect": "auto",
    "webkitWritingMode": "horizontal-tb",
    "whiteSpace": "normal",
    "whiteSpaceCollapse": "collapse",
    "widows": "2",
    "width": "48px",
    "willChange": "auto",
    "wordBreak": "normal",
    "wordSpacing": "0px",
    "wordWrap": "normal",
    "writingMode": "horizontal-tb",
    "x": "0px",
    "y": "0px",

:::info 面试题
[样式计算具体步骤](./meeting_question.md#computed_style)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017

3. 布局 —— Layout

根据 DOM 树中的样式，计算出每个节点的尺寸和位置。

alt text

这个过程很复杂，因为页面上元素之间是会互相影响的。

尺寸

因为有的元素宽高是相对的，所以在上一步样式计算中是不会进行宽高的计算的。在当前这步才能计算。

位置

相对包含块的位置。

DOM 树和 Layout 树不一定是一一对应的

因为 Layout 树是找到每个节点的几何信息的，所以有些隐藏的节点是不会在 Layout 树中的。

DOM 树中存在但布局树中不存在的

head
display:none

DOM 树中不存在但布局树中存在的

::before 伪元素

`head` 节点为什么是隐藏的

浏览器默认样式中让 head 隐藏

匿名行盒块盒

alt text

内容必须在行盒中
行盒和块盒不能相邻
布局树会添加匿名行盒和块盒 (这三条是 w3c 说的。)

布局树不是 DOM 对象

布局树是 C++ 对象，JS 操作不到。

面试题

怎么进行布局的 —— 布局

4. 分层 —— Layer

分层是现代浏览器新引入的机制。为了只更新频繁变动的部分。

alt text

在【浏览器 F12 - 右上角三个点 - 更多工具（More tools）- 图层（Layers）】中。

alt text

浏览器内部有分层策略，不需要我们关心。有些跟堆叠上下文相关的 CSS 属性会影响到分层。

z-index
opacity
transform

不是一定会有影响，只是会影响浏览器的决策。

有一个特殊的 CSS 属性 will-change，会影响分层决策。如果某个元素会频繁变化，但浏览器还没为其单独分层，可以使用这个属性让浏览器把它单独分层。

css

will-change: transform;

面试题

分层

5. 绘制 —— Painted

alt text

生成绘制指令。例如

将笔尖移动到 10, 30
画一个 200 * 300 的矩形
使用红色填充
将笔尖移动到 ...

类似 canvas，实际上 canvas 中用的就是浏览器内核中的绘制指令。

渲染主线程的工作到此为止了，剩余步骤交给其它线程处理。

alt text

面试题

绘制

6. 分块 —— Tiling

将每一层都划分为小的区域，按优先级处理。

优先级

先画视口附近的块。

多线程处理

合成线程做分块，启动更多线程一起处理。

alt text

可以使用系统工具（Mac 系统的活动监视器）来查看。

alt text

面试题

分块

7. 光栅化 —— Raster

将每个块变成位图。

会优先处理视口附近的块。

alt text

光栅化过程中会使用 GPU 进行加速。

alt text

面试题

光栅化

8. 画 —— Draw

将每个块按照指引信息（quad）交给 GPU 进程，GPU 进程将其交给硬件（显卡），最终呈现。

alt text

为什么要在 GPU 进程中中转

而不是直接交给硬件呢？

因为渲染主线程和合成进程都在渲染进程中，是沙盒环境，而找硬件是系统调用。因此浏览网页过程中不会导致计算机遭受攻击。

transform 是在这步才进行处理的

因为 transform 是在 GPU 中进行矩阵变换。

transform 为什么效率高

GPU 处理矩阵变换快

面试题

画

完整过程

alt text

解析 html 生成 dom 树和 cssom 树
计算样式让每个 dom 得到最终样式
布局计算每个 dom 节点的几何信息
布局树和 dom 树不一样，不能一一对应
分层为了提高后续的渲染效率，把页面分为图层，单独进行绘制
绘制产生绘制指令
分块绘制指令交给合成线程进行分块
光栅化对每个层的每个小块进行光栅化，输出位图。优先处理视口附近的小块。
画

浏览器渲染原理 ​

啥叫渲染 —— Render ​

渲染时间点 ​

1. 解析 HTML —— Parse HTML ​

DOM 树 ​

CSSOM 树 ​

HTML 过程解析过程中遇到 CSS 怎么办 ​

HTML 解析过程中遇到 JS 怎么办 ​

2. 样式计算 —— Recalculate Style ​

最终样式 ​

获取计算后的样式 ​

3. 布局 —— Layout ​

尺寸 ​

位置 ​

DOM 树和 Layout 树不一定是一一对应的 ​

DOM 树中存在但布局树中不存在的 ​

DOM 树中不存在但布局树中存在的 ​

head 节点为什么是隐藏的 ​

匿名行盒块盒 ​

布局树不是 DOM 对象 ​

4. 分层 —— Layer ​

5. 绘制 —— Painted ​

6. 分块 —— Tiling ​

优先级 ​

多线程处理 ​

7. 光栅化 —— Raster ​

8. 画 —— Draw ​

为什么要在 GPU 进程中中转 ​

transform 是在这步才进行处理的 ​

transform 为什么效率高 ​

完整过程 ​

浏览器渲染原理

啥叫渲染 —— Render

渲染时间点

1. 解析 HTML —— Parse HTML

DOM 树

CSSOM 树

HTML 过程解析过程中遇到 CSS 怎么办

HTML 解析过程中遇到 JS 怎么办

2. 样式计算 —— Recalculate Style

最终样式

获取计算后的样式

3. 布局 —— Layout

尺寸

位置

DOM 树和 Layout 树不一定是一一对应的

DOM 树中存在但布局树中不存在的

DOM 树中不存在但布局树中存在的

`head` 节点为什么是隐藏的

匿名行盒块盒

布局树不是 DOM 对象

4. 分层 —— Layer

5. 绘制 —— Painted

6. 分块 —— Tiling

优先级

多线程处理

7. 光栅化 —— Raster

8. 画 —— Draw

为什么要在 GPU 进程中中转

transform 是在这步才进行处理的

transform 为什么效率高

完整过程