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856 lines
49 KiB
856 lines
49 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html lang="en-US-x-Hixie" ><head><title>4.8.11 The canvas element — HTML5 </title><style type="text/css">
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pre { margin-left: 2em; white-space: pre-wrap; }
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h2 { margin: 3em 0 1em 0; }
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h3 { margin: 2.5em 0 1em 0; }
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h4 { margin: 2.5em 0 0.75em 0; }
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h5, h6 { margin: 2.5em 0 1em; }
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h1 + h2, h1 + h2 + h2 { margin: 0.75em 0 0.75em; }
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h2 + h3, h3 + h4, h4 + h5, h5 + h6 { margin-top: 0.5em; }
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p { margin: 1em 0; }
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hr:not(.top) { display: block; background: none; border: none; padding: 0; margin: 2em 0; height: auto; }
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dl, dd { margin-top: 0; margin-bottom: 0; }
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dt { margin-top: 0.75em; margin-bottom: 0.25em; clear: left; }
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dt + dt { margin-top: 0; }
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dd dt { margin-top: 0.25em; margin-bottom: 0; }
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dd p { margin-top: 0; }
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dd dl + p { margin-top: 1em; }
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dd table + p { margin-top: 1em; }
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p + * > li, dd li { margin: 1em 0; }
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dt, dfn { font-weight: bold; font-style: normal; }
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dt dfn { font-style: italic; }
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pre, code { font-size: inherit; font-family: monospace; font-variant: normal; }
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pre strong { color: black; font: inherit; font-weight: bold; background: yellow; }
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pre em { font-weight: bolder; font-style: normal; }
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@media screen { code { color: orangered; } code :link, code :visited { color: inherit; } }
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var sub { vertical-align: bottom; font-size: smaller; position: relative; top: 0.1em; }
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table { border-collapse: collapse; border-style: hidden hidden none hidden; }
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table thead, table tbody { border-bottom: solid; }
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table tbody th:first-child { border-left: solid; }
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table tbody th { text-align: left; }
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table td, table th { border-left: solid; border-right: solid; border-bottom: solid thin; vertical-align: top; padding: 0.2em; }
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blockquote { margin: 0 0 0 2em; border: 0; padding: 0; font-style: italic; }
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.bad, .bad *:not(.XXX) { color: gray; border-color: gray; background: transparent; }
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.matrix, .matrix td { border: none; text-align: right; }
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.matrix { margin-left: 2em; }
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.dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
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.dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
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.dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }
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.toc dfn, h1 dfn, h2 dfn, h3 dfn, h4 dfn, h5 dfn, h6 dfn { font: inherit; }
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img.extra { float: right; }
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pre.idl { border: solid thin; background: #EEEEEE; color: black; padding: 0.5em 1em; }
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pre.idl :link, pre.idl :visited { color: inherit; background: transparent; }
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pre.css { border: solid thin; background: #FFFFEE; color: black; padding: 0.5em 1em; }
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pre.css:first-line { color: #AAAA50; }
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dl.domintro { color: green; margin: 2em 0 2em 2em; padding: 0.5em 1em; border: none; background: #DDFFDD; }
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hr + dl.domintro, div.impl + dl.domintro { margin-top: 2.5em; margin-bottom: 1.5em; }
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dl.domintro dt, dl.domintro dt * { color: black; text-decoration: none; }
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dl.domintro dd { margin: 0.5em 0 1em 2em; padding: 0; }
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dl.domintro dd p { margin: 0.5em 0; }
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dl.switch { padding-left: 2em; }
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dl.switch > dt { text-indent: -1.5em; }
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dl.switch > dt:before { content: '\21AA'; padding: 0 0.5em 0 0; display: inline-block; width: 1em; text-align: right; line-height: 0.5em; }
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dl.triple { padding: 0 0 0 1em; }
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dl.triple dt, dl.triple dd { margin: 0; display: inline }
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dl.triple dt:after { content: ':'; }
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dl.triple dd:after { content: '\A'; white-space: pre; }
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.diff-old { text-decoration: line-through; color: silver; background: transparent; }
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.diff-chg, .diff-new { text-decoration: underline; color: green; background: transparent; }
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a .diff-new { border-bottom: 1px blue solid; }
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h2 { page-break-before: always; }
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h1, h2, h3, h4, h5, h6 { page-break-after: avoid; }
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h1 + h2, hr + h2.no-toc { page-break-before: auto; }
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p > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]),
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li > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]), { border-bottom: solid #9999CC; }
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div.head { margin: 0 0 1em; padding: 1em 0 0 0; }
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div.head p { margin: 0; }
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div.head h1 { margin: 0; }
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div.head .logo { float: right; margin: 0 1em; }
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div.head .logo img { border: none } /* remove border from top image */
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div.head dl { margin: 1em 0; }
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div.head p.copyright, div.head p.alt { font-size: x-small; font-style: oblique; margin: 0; }
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body > .toc > li { margin-top: 1em; margin-bottom: 1em; }
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body > .toc.brief > li { margin-top: 0.35em; margin-bottom: 0.35em; }
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body > .toc > li > * { margin-bottom: 0.5em; }
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body > .toc > li > * > li > * { margin-bottom: 0.25em; }
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.toc, .toc li { list-style: none; }
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.brief { margin-top: 1em; margin-bottom: 1em; line-height: 1.1; }
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.brief li { margin: 0; padding: 0; }
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.category-list li { display: inline; }
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.category-list li:not(:last-child)::after { content: ', '; }
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.category-list li > span, .category-list li > a { text-transform: lowercase; }
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.category-list li * { text-transform: none; } /* don't affect <code> nested in <a> */
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.XXX { color: #E50000; background: white; border: solid red; padding: 0.5em; margin: 1em 0; }
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.XXX > :first-child { margin-top: 0; }
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p .XXX { line-height: 3em; }
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.annotation { border: solid thin black; background: #0C479D; color: white; position: relative; margin: 8px 0 20px 0; }
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.annotation:before { position: absolute; left: 0; top: 0; width: 100%; height: 100%; margin: 6px -6px -6px 6px; background: #333333; z-index: -1; content: ''; }
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.annotation :link, .annotation :visited { color: inherit; }
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.annotation :link:hover, .annotation :visited:hover { background: transparent; }
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.annotation span { border: none ! important; }
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.note { color: green; background: transparent; font-family: sans-serif; }
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.warning { color: red; background: transparent; }
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.note, .warning { font-weight: bolder; font-style: italic; }
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p.note, div.note { padding: 0.5em 2em; }
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span.note { padding: 0 2em; }
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.note p:last-child, .warning p:last-child { margin-bottom: 0; }
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.warning:before { font-style: normal; }
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p.note:before { content: 'Note: '; }
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p.warning:before { content: '\26A0 Warning! '; }
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.bookkeeping:before { display: block; content: 'Bookkeeping details'; font-weight: bolder; font-style: italic; }
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.bookkeeping { font-size: 0.8em; margin: 2em 0; }
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.bookkeeping p { margin: 0.5em 2em; display: list-item; list-style: square; }
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.bookkeeping dt { margin: 0.5em 2em 0; }
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.bookkeeping dd { margin: 0 3em 0.5em; }
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h4 { position: relative; z-index: 3; }
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h4 + .element, h4 + div + .element { margin-top: -2.5em; padding-top: 2em; }
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.element {
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background: #EEEEFF;
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color: black;
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margin: 0 0 1em 0.15em;
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padding: 0 1em 0.25em 0.75em;
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border-left: solid #9999FF 0.25em;
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position: relative;
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z-index: 1;
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}
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.element:before {
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position: absolute;
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z-index: 2;
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top: 0;
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left: -1.15em;
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height: 2em;
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width: 0.9em;
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background: #EEEEFF;
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content: ' ';
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border-style: none none solid solid;
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border-color: #9999FF;
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border-width: 0.25em;
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}
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.example { display: block; color: #222222; background: #FCFCFC; border-left: double; margin-left: 2em; padding-left: 1em; }
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td > .example:only-child { margin: 0 0 0 0.1em; }
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ul.domTree, ul.domTree ul { padding: 0 0 0 1em; margin: 0; }
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ul.domTree li { padding: 0; margin: 0; list-style: none; position: relative; }
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ul.domTree li li { list-style: none; }
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ul.domTree li:first-child::before { position: absolute; top: 0; height: 0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
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ul.domTree li:not(:last-child)::after { position: absolute; top: 0; bottom: -0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
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ul.domTree span { font-style: italic; font-family: serif; }
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ul.domTree .t1 code { color: purple; font-weight: bold; }
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ul.domTree .t2 { font-style: normal; font-family: monospace; }
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ul.domTree .t2 .name { color: black; font-weight: bold; }
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ul.domTree .t2 .value { color: blue; font-weight: normal; }
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ul.domTree .t3 code, .domTree .t4 code, .domTree .t5 code { color: gray; }
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ul.domTree .t7 code, .domTree .t8 code { color: green; }
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ul.domTree .t10 code { color: teal; }
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body.dfnEnabled dfn { cursor: pointer; }
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.dfnPanel {
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display: inline;
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position: absolute;
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z-index: 10;
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height: auto;
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width: auto;
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padding: 0.5em 0.75em;
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font: small sans-serif, Droid Sans Fallback;
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background: #DDDDDD;
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color: black;
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border: outset 0.2em;
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}
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.dfnPanel * { margin: 0; padding: 0; font: inherit; text-indent: 0; }
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.dfnPanel :link, .dfnPanel :visited { color: black; }
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.dfnPanel p { font-weight: bolder; }
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.dfnPanel * + p { margin-top: 0.25em; }
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.dfnPanel li { list-style-position: inside; }
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#configUI { position: absolute; z-index: 20; top: 10em; right: 1em; width: 11em; font-size: small; }
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#configUI p { margin: 0.5em 0; padding: 0.3em; background: #EEEEEE; color: black; border: inset thin; }
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#configUI p label { display: block; }
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#configUI #updateUI, #configUI .loginUI { text-align: center; }
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#configUI input[type=button] { display: block; margin: auto; }
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fieldset { margin: 1em; padding: 0.5em 1em; }
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fieldset > legend + * { margin-top: 0; }
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fieldset > :last-child { margin-bottom: 0; }
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fieldset p { margin: 0.5em 0; }
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.stability {
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position: fixed;
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bottom: 0;
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left: 0; right: 0;
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margin: 0 auto 0 auto !important;
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z-index: 1000;
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width: 50%;
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background: maroon; color: yellow;
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-webkit-border-radius: 1em 1em 0 0;
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-moz-border-radius: 1em 1em 0 0;
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border-radius: 1em 1em 0 0;
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-moz-box-shadow: 0 0 1em #500;
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-webkit-box-shadow: 0 0 1em #500;
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box-shadow: 0 0 1em red;
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padding: 0.5em 1em;
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text-align: center;
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}
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.stability strong {
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display: block;
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}
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.stability input {
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appearance: none; margin: 0; border: 0; padding: 0.25em 0.5em; background: transparent; color: black;
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position: absolute; top: -0.5em; right: 0; font: 1.25em sans-serif; text-align: center;
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}
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.stability input:hover {
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color: white;
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text-shadow: 0 0 2px black;
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}
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.stability input:active {
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padding: 0.3em 0.45em 0.2em 0.55em;
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}
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.stability :link, .stability :visited,
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.stability :link:hover, .stability :visited:hover {
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background: transparent;
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color: white;
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}
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</style><link href="data:text/css,.impl%20%7B%20display:%20none;%20%7D%0Ahtml%20%7B%20border:%20solid%20yellow;%20%7D%20.domintro:before%20%7B%20display:%20none;%20%7D" id="author" rel="alternate stylesheet" title="Author documentation only"><link href="data:text/css,.impl%20%7B%20background:%20%23FFEEEE;%20%7D%20.domintro:before%20%7B%20background:%20%23FFEEEE;%20%7D" id="highlight" rel="alternate stylesheet" title="Highlight implementation
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requirements"><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css"><style type="text/css">
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.applies thead th > * { display: block; }
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.applies thead code { display: block; }
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.applies tbody th { whitespace: nowrap; }
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.applies td { text-align: center; }
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.applies .yes { background: yellow; }
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.matrix, .matrix td { border: hidden; text-align: right; }
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.matrix { margin-left: 2em; }
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.dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
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.dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
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.dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }
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td.eg { border-width: thin; text-align: center; }
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#table-example-1 { border: solid thin; border-collapse: collapse; margin-left: 3em; }
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#table-example-1 * { font-family: "Essays1743", serif; line-height: 1.01em; }
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#table-example-1 caption { padding-bottom: 0.5em; }
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#table-example-1 thead, #table-example-1 tbody { border: none; }
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#table-example-1 th, #table-example-1 td { border: solid thin; }
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#table-example-1 th { font-weight: normal; }
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#table-example-1 td { border-style: none solid; vertical-align: top; }
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#table-example-1 th { padding: 0.5em; vertical-align: middle; text-align: center; }
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#table-example-1 tbody tr:first-child td { padding-top: 0.5em; }
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#table-example-1 tbody tr:last-child td { padding-bottom: 1.5em; }
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#table-example-1 tbody td:first-child { padding-left: 2.5em; padding-right: 0; width: 9em; }
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#table-example-1 tbody td:first-child::after { content: leader(". "); }
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#table-example-1 tbody td { padding-left: 2em; padding-right: 2em; }
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#table-example-1 tbody td:first-child + td { width: 10em; }
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#table-example-1 tbody td:first-child + td ~ td { width: 2.5em; }
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#table-example-1 tbody td:first-child + td + td + td ~ td { width: 1.25em; }
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.apple-table-examples { border: none; border-collapse: separate; border-spacing: 1.5em 0em; width: 40em; margin-left: 3em; }
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.apple-table-examples * { font-family: "Times", serif; }
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.apple-table-examples td, .apple-table-examples th { border: none; white-space: nowrap; padding-top: 0; padding-bottom: 0; }
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.apple-table-examples tbody th:first-child { border-left: none; width: 100%; }
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.apple-table-examples thead th:first-child ~ th { font-size: smaller; font-weight: bolder; border-bottom: solid 2px; text-align: center; }
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.apple-table-examples tbody th::after, .apple-table-examples tfoot th::after { content: leader(". ") }
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.apple-table-examples tbody th, .apple-table-examples tfoot th { font: inherit; text-align: left; }
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.apple-table-examples td { text-align: right; vertical-align: top; }
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.apple-table-examples.e1 tbody tr:last-child td { border-bottom: solid 1px; }
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.apple-table-examples.e1 tbody + tbody tr:last-child td { border-bottom: double 3px; }
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.apple-table-examples.e2 th[scope=row] { padding-left: 1em; }
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.apple-table-examples sup { line-height: 0; }
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.details-example img { vertical-align: top; }
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#base64-table {
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white-space: nowrap;
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font-size: 0.6em;
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column-width: 6em;
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column-count: 5;
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column-gap: 1em;
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-moz-column-width: 6em;
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-moz-column-count: 5;
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-moz-column-gap: 1em;
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-webkit-column-width: 6em;
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-webkit-column-count: 5;
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-webkit-column-gap: 1em;
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}
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#base64-table thead { display: none; }
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#base64-table * { border: none; }
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#base64-table tbody td:first-child:after { content: ':'; }
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#base64-table tbody td:last-child { text-align: right; }
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#named-character-references-table {
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white-space: nowrap;
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font-size: 0.6em;
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column-width: 30em;
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column-gap: 1em;
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-moz-column-width: 30em;
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-moz-column-gap: 1em;
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-webkit-column-width: 30em;
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-webkit-column-gap: 1em;
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}
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#named-character-references-table > table > tbody > tr > td:first-child + td,
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#named-character-references-table > table > tbody > tr > td:last-child { text-align: center; }
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#named-character-references-table > table > tbody > tr > td:last-child:hover > span { position: absolute; top: auto; left: auto; margin-left: 0.5em; line-height: 1.2; font-size: 5em; border: outset; padding: 0.25em 0.5em; background: white; width: 1.25em; height: auto; text-align: center; }
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#named-character-references-table > table > tbody > tr#entity-CounterClockwiseContourIntegral > td:first-child { font-size: 0.5em; }
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.glyph.control { color: red; }
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@font-face {
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font-family: 'Essays1743';
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743.ttf');
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}
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@font-face {
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font-family: 'Essays1743';
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font-weight: bold;
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Bold.ttf');
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}
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@font-face {
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font-family: 'Essays1743';
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font-style: italic;
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Italic.ttf');
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}
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@font-face {
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font-family: 'Essays1743';
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font-style: italic;
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font-weight: bold;
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-BoldItalic.ttf');
|
|
}
|
|
|
|
</style><style type="text/css">
|
|
.domintro:before { display: table; margin: -1em -0.5em -0.5em auto; width: auto; content: 'This box is non-normative. Implementation requirements are given below this box.'; color: black; font-style: italic; border: solid 2px; background: white; padding: 0 0.25em; }
|
|
</style><script type="text/javascript">
|
|
function getCookie(name) {
|
|
var params = location.search.substr(1).split("&");
|
|
for (var index = 0; index < params.length; index++) {
|
|
if (params[index] == name)
|
|
return "1";
|
|
var data = params[index].split("=");
|
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if (data[0] == name)
|
|
return unescape(data[1]);
|
|
}
|
|
var cookies = document.cookie.split("; ");
|
|
for (var index = 0; index < cookies.length; index++) {
|
|
var data = cookies[index].split("=");
|
|
if (data[0] == name)
|
|
return unescape(data[1]);
|
|
}
|
|
return null;
|
|
}
|
|
</script>
|
|
<script src="link-fixup.js" type="text/javascript"></script>
|
|
<link href="style.css" rel="stylesheet"><link href="the-iframe-element.html" title="4.8.2 The iframe element" rel="prev">
|
|
<link href="spec.html#contents" title="Table of contents" rel="index">
|
|
<link href="the-map-element.html" title="4.8.12 The map element" rel="next">
|
|
</head><body><div class="head" id="head">
|
|
<div id="multipage-common">
|
|
<p class="stability" id="wip"><strong>This is a work in
|
|
progress!</strong> For the latest updates from the HTML WG, possibly
|
|
including important bug fixes, please look at the <a href="http://dev.w3.org/html5/spec/Overview.html">editor's draft</a> instead.
|
|
There may also be a more
|
|
<a href="http://www.w3.org/TR/html5">up-to-date Working Draft</a>
|
|
with changes based on resolution of Last Call issues.
|
|
<input onclick="closeWarning(this.parentNode)" type="button" value="╳⃝"></p>
|
|
<script type="text/javascript">
|
|
function closeWarning(element) {
|
|
element.parentNode.removeChild(element);
|
|
var date = new Date();
|
|
date.setDate(date.getDate()+4);
|
|
document.cookie = 'hide-obsolescence-warning=1; expires=' + date.toGMTString();
|
|
}
|
|
if (getCookie('hide-obsolescence-warning') == '1')
|
|
setTimeout(function () { document.getElementById('wip').parentNode.removeChild(document.getElementById('wip')); }, 2000);
|
|
</script></div>
|
|
|
|
<p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="http://www.w3.org/Icons/w3c_home" width="72"></a></p>
|
|
|
|
<h1>HTML5</h1>
|
|
</div><div>
|
|
<a href="the-iframe-element.html" class="prev">4.8.2 The iframe element</a> –
|
|
<a href="spec.html#contents">Table of contents</a> –
|
|
<a href="the-map-element.html" class="next">4.8.12 The map element</a>
|
|
<ol class="toc"><li><ol><li><ol><li><a href="the-canvas-element.html#the-canvas-element"><span class="secno">4.8.11 </span>The <code>canvas</code> element</a>
|
|
<ol><li><a href="the-canvas-element.html#color-spaces-and-color-correction"><span class="secno">4.8.11.1 </span>Color spaces and color correction</a></li><li><a href="the-canvas-element.html#security-with-canvas-elements"><span class="secno">4.8.11.2 </span>Security with <code>canvas</code> elements</a></li></ol></li></ol></li></ol></li></ol></div>
|
|
|
|
<h4 id="the-canvas-element"><span class="secno">4.8.11 </span>The <dfn id="canvas"><code>canvas</code></dfn> element</h4><dl class="element"><dt>Categories</dt>
|
|
<dd><a href="content-models.html#flow-content">Flow content</a>.</dd>
|
|
<dd><a href="content-models.html#phrasing-content">Phrasing content</a>.</dd>
|
|
<dd><a href="content-models.html#embedded-content">Embedded content</a>.</dd>
|
|
<dt>Contexts in which this element can be used:</dt>
|
|
<dd>Where <a href="content-models.html#embedded-content">embedded content</a> is expected.</dd>
|
|
<dt>Content model:</dt>
|
|
<dd><a href="content-models.html#transparent">Transparent</a>.</dd>
|
|
<dt>Content attributes:</dt>
|
|
<dd><a href="elements.html#global-attributes">Global attributes</a></dd>
|
|
<dd><code title="attr-canvas-width"><a href="#attr-canvas-width">width</a></code></dd>
|
|
<dd><code title="attr-canvas-height"><a href="#attr-canvas-height">height</a></code></dd>
|
|
<dt>DOM interface:</dt>
|
|
<dd>
|
|
<pre class="idl">interface <dfn id="htmlcanvaselement">HTMLCanvasElement</dfn> : <a href="elements.html#htmlelement">HTMLElement</a> {
|
|
attribute unsigned long <a href="#dom-canvas-width" title="dom-canvas-width">width</a>;
|
|
attribute unsigned long <a href="#dom-canvas-height" title="dom-canvas-height">height</a>;
|
|
|
|
DOMString <a href="#dom-canvas-todataurl" title="dom-canvas-toDataURL">toDataURL</a>(in optional DOMString type, in any... args);
|
|
void <a href="#dom-canvas-toblob" title="dom-canvas-toBlob">toBlob</a>(in <span>FileCallback</span>, in optional DOMString type, in any... args);
|
|
|
|
object <a href="#dom-canvas-getcontext" title="dom-canvas-getContext">getContext</a>(in DOMString contextId, in any... args);
|
|
};</pre>
|
|
</dd>
|
|
</dl><p>The <code><a href="#the-canvas-element">canvas</a></code> element provides scripts with a
|
|
resolution-dependent bitmap canvas, which can be used for rendering
|
|
graphs, game graphics, or other visual images on the fly.</p><p>Authors should not use the <code><a href="#the-canvas-element">canvas</a></code> element in a
|
|
document when a more suitable element is available. For example, it
|
|
is inappropriate to use a <code><a href="#the-canvas-element">canvas</a></code> element to render a
|
|
page heading: if the desired presentation of the heading is
|
|
graphically intense, it should be marked up using appropriate
|
|
elements (typically <code><a href="sections.html#the-h1-h2-h3-h4-h5-and-h6-elements">h1</a></code>) and then styled using CSS and
|
|
supporting technologies such as XBL.</p><p>When authors use the <code><a href="#the-canvas-element">canvas</a></code> element, they must also
|
|
provide content that, when presented to the user, conveys
|
|
essentially the same function or purpose as the bitmap canvas. This
|
|
content may be placed as content of the <code><a href="#the-canvas-element">canvas</a></code>
|
|
element. The contents of the <code><a href="#the-canvas-element">canvas</a></code> element, if any,
|
|
are the element's <a href="content-models.html#fallback-content">fallback content</a>.</p><p>In interactive visual media, if <a href="webappapis.html#concept-n-script" title="concept-n-script">scripting is enabled</a> for the
|
|
<code><a href="#the-canvas-element">canvas</a></code> element, and if support for <code><a href="#the-canvas-element">canvas</a></code>
|
|
elements has been enabled, the <code><a href="#the-canvas-element">canvas</a></code> element
|
|
<a href="rendering.html#represents">represents</a> <a href="content-models.html#embedded-content">embedded content</a> consisting of
|
|
a dynamically created image.</p><p>In non-interactive, static, visual media, if the
|
|
<code><a href="#the-canvas-element">canvas</a></code> element has been previously painted on (e.g. if
|
|
the page was viewed in an interactive visual medium and is now being
|
|
printed, or if some script that ran during the page layout process
|
|
painted on the element), then the <code><a href="#the-canvas-element">canvas</a></code> element
|
|
<a href="rendering.html#represents">represents</a> <a href="content-models.html#embedded-content">embedded content</a> with the
|
|
current image and size. Otherwise, the element represents its
|
|
<a href="content-models.html#fallback-content">fallback content</a> instead.</p><p>In non-visual media, and in visual media if <a href="webappapis.html#concept-n-noscript" title="concept-n-noscript">scripting is disabled</a> for the
|
|
<code><a href="#the-canvas-element">canvas</a></code> element or if support for <code><a href="#the-canvas-element">canvas</a></code>
|
|
elements has been disabled, the <code><a href="#the-canvas-element">canvas</a></code> element
|
|
<a href="rendering.html#represents">represents</a> its <a href="content-models.html#fallback-content">fallback content</a>
|
|
instead.</p><!-- CANVAS-FOCUS-FALLBACK --><p>When a <code><a href="#the-canvas-element">canvas</a></code> element <a href="rendering.html#represents">represents</a>
|
|
<a href="content-models.html#embedded-content">embedded content</a>, the user can still focus descendants
|
|
of the <code><a href="#the-canvas-element">canvas</a></code> element (in the <a href="content-models.html#fallback-content">fallback
|
|
content</a>). When an element is focused, it is the target of
|
|
keyboard interaction events (even though the element itself is not
|
|
visible). This allows authors to make an interactive canvas
|
|
keyboard-accessible: authors should have a one-to-one mapping of
|
|
interactive regions to focusable elements in the <a href="content-models.html#fallback-content">fallback
|
|
content</a>. (Focus has no effect on mouse interaction
|
|
events.) <a href="references.html#refsDOMEVENTS">[DOMEVENTS]</a></p><p>The <code><a href="#the-canvas-element">canvas</a></code> element has two attributes to control the
|
|
size of the coordinate space: <dfn id="attr-canvas-width" title="attr-canvas-width"><code>width</code></dfn> and <dfn id="attr-canvas-height" title="attr-canvas-height"><code>height</code></dfn>. These
|
|
attributes, when specified, must have values that are <a href="common-microsyntaxes.html#valid-non-negative-integer" title="valid non-negative integer">valid non-negative
|
|
integers</a>. <span class="impl">The <a href="common-microsyntaxes.html#rules-for-parsing-non-negative-integers">rules for parsing
|
|
non-negative integers</a> must be used to obtain their numeric
|
|
values. If an attribute is missing, or if parsing its value returns
|
|
an error, then the default value must be used instead.</span> The
|
|
<code title="attr-canvas-width"><a href="#attr-canvas-width">width</a></code> attribute defaults to
|
|
300, and the <code title="attr-canvas-height"><a href="#attr-canvas-height">height</a></code>
|
|
attribute defaults to 150.</p><p>The intrinsic dimensions of the <code><a href="#the-canvas-element">canvas</a></code> element equal
|
|
the size of the coordinate space, with the numbers interpreted in
|
|
CSS pixels. However, the element can be sized arbitrarily by a
|
|
style sheet. During rendering, the image is scaled to fit this layout
|
|
size.</p><div class="impl">
|
|
|
|
<p>The size of the coordinate space does not necessarily represent
|
|
the size of the actual bitmap that the user agent will use
|
|
internally or during rendering. On high-definition displays, for
|
|
instance, the user agent may internally use a bitmap with two device
|
|
pixels per unit in the coordinate space, so that the rendering
|
|
remains at high quality throughout.</p>
|
|
|
|
<p>When the <code><a href="#the-canvas-element">canvas</a></code> element is created, and subsequently
|
|
whenever the <code title="attr-canvas-width"><a href="#attr-canvas-width">width</a></code> and <code title="attr-canvas-height"><a href="#attr-canvas-height">height</a></code> attributes are set (whether
|
|
to a new value or to the previous value), the bitmap and any
|
|
associated contexts must be cleared back to their initial state and
|
|
reinitialized with the newly specified coordinate space
|
|
dimensions.</p>
|
|
|
|
<p>When the canvas is initialized, its bitmap must be cleared to
|
|
transparent black.</p>
|
|
|
|
<p>The <dfn id="dom-canvas-width" title="dom-canvas-width"><code>width</code></dfn> and
|
|
<dfn id="dom-canvas-height" title="dom-canvas-height"><code>height</code></dfn> IDL
|
|
attributes must <a href="common-dom-interfaces.html#reflect">reflect</a> the respective content
|
|
attributes of the same name, with the same defaults.</p>
|
|
|
|
</div><div class="example">
|
|
<p>Only one square appears to be drawn in the following example:</p>
|
|
<pre> // canvas is a reference to a <canvas> element
|
|
var context = canvas.getContext('2d');
|
|
context.fillRect(0,0,50,50);
|
|
canvas.setAttribute('width', '300'); // clears the canvas
|
|
context.fillRect(0,100,50,50);
|
|
canvas.width = canvas.width; // clears the canvas
|
|
context.fillRect(100,0,50,50); // only this square remains</pre>
|
|
</div><hr><dl class="domintro"><dt><var title="">context</var> = <var title="">canvas</var> . <code title="dom-canvas-getContext"><a href="#dom-canvas-getcontext">getContext</a></code>(<var title="">contextId</var> [, ... ])</dt>
|
|
|
|
<dd>
|
|
|
|
<p>Returns an object that exposes an API for drawing on the
|
|
canvas. The first argument specifies the desired API. Subsequent
|
|
arguments are handled by that API.</p>
|
|
|
|
|
|
<p>The list of defined contexts is given on the <a href="http://wiki.whatwg.org/wiki/CanvasContexts">WHATWG Wiki
|
|
CanvasContexts page</a>. <a href="references.html#refsWHATWGWIKI">[WHATWGWIKI]</a>
|
|
|
|
</p><p>Returns null if the given context ID is not supported or if the
|
|
canvas has already been initialised with some other (incompatible)
|
|
context type (e.g. trying to get a "<code title="canvas-context-2d">2d</code>" context after getting a
|
|
"<code title="canvas-context-webgl">webgl</code>" context).</p>
|
|
|
|
</dd>
|
|
|
|
</dl><div class="impl">
|
|
|
|
<p>A <code><a href="#the-canvas-element">canvas</a></code> element can have a <dfn id="primary-context">primary
|
|
context</dfn>, which is the first context to have been obtained for
|
|
that element. When created, a <code><a href="#the-canvas-element">canvas</a></code> element must not
|
|
have a <a href="#primary-context">primary context</a>.</p>
|
|
|
|
<p>The most commonly used primary context is the <a href="http://dev.w3.org/html5/2dcontext/">HTML Canvas 2D Context</a>.
|
|
|
|
</p><p>The <dfn id="dom-canvas-getcontext" title="dom-canvas-getContext"><code>getContext(<var title="">contextId</var>, <var title="">args...</var>)</code></dfn>
|
|
method of the <code><a href="#the-canvas-element">canvas</a></code> element, when invoked, must run
|
|
the following steps:</p>
|
|
|
|
<ol><li><p>Let <var title="">contextId</var> be the first argument to
|
|
the method.</p></li>
|
|
|
|
<li>
|
|
|
|
<p>If <var title="">contextId</var> is not the name of a context
|
|
supported by the user agent, return null and abort these
|
|
steps.</p>
|
|
|
|
<p class="note">An example of this would be a user agent that
|
|
theoretically supports the "<code title="canvas-context-webgl">webgl</code>" 3D context, in the case
|
|
where the platform does not have hardware support for OpenGL and
|
|
the user agent does not have a software OpenGL implementation.
|
|
Despite the user agent recognising the "<code title="canvas-context-webgl">webgl</code>" name, it would return
|
|
null at this step because that context is not, in practice,
|
|
supported at the time of the call.</p>
|
|
|
|
</li>
|
|
|
|
<li><p>If the element has a <a href="#primary-context">primary context</a> and that
|
|
context's entry in the <a href="http://wiki.whatwg.org/wiki/CanvasContexts">WHATWG Wiki
|
|
CanvasContexts page</a> does not list <var title="">contextId</var>
|
|
as a context with which it is compatible, return null and abort
|
|
these steps. <a href="references.html#refsWHATWGWIKI">[WHATWGWIKI]</a></p></li>
|
|
|
|
<li><p>If the element does not have a <a href="#primary-context">primary context</a>,
|
|
let the element's <a href="#primary-context">primary context</a> be <var title="">contextId</var>.</p></li>
|
|
|
|
<li><p>If the <code title="dom-canvas-getContext"><a href="#dom-canvas-getcontext">getContext()</a></code> method has
|
|
already been invoked on this element for the same <var title="">contextId</var>, return the same object as was returned
|
|
that time, and abort these steps. The additional arguments are
|
|
ignored.</p></li>
|
|
|
|
<li><p><dfn id="getcontext-return" title="getContext-return">Return a new object for <var title="">contextId</var></dfn>, as defined by the specification
|
|
given for <var title="">contextId</var>'s entry in the <a href="http://wiki.whatwg.org/wiki/CanvasContexts">WHATWG Wiki
|
|
CanvasContexts page</a>. <a href="references.html#refsWHATWGWIKI">[WHATWGWIKI]</a></p></li>
|
|
|
|
</ol><p>New context types may be registered in the <a href="http://wiki.whatwg.org/wiki/CanvasContexts">WHATWG Wiki
|
|
CanvasContexts page</a>. <a href="references.html#refsWHATWGWIKI">[WHATWGWIKI]</a></p>
|
|
|
|
<p>Anyone is free to edit the WHATWG Wiki CanvasContexts page at any
|
|
time to add a new context type. These new context types must be
|
|
specified with the following information:</p>
|
|
|
|
<dl><dt>Keyword</dt>
|
|
|
|
<dd><p>The value of <var title="">contextID</var> that will return
|
|
the object for the new API.</p></dd>
|
|
|
|
|
|
<dt>Specification</dt>
|
|
|
|
<dd><p>A link to a formal specification of the context type's
|
|
API. It could be another page on the Wiki, or a link to an external
|
|
page. If the type does not have a formal specification, an informal
|
|
description can be substituted until such time as a formal
|
|
specification is available.</p></dd>
|
|
|
|
|
|
<dt>Compatible with</dt>
|
|
|
|
<dd><p>The list of context types that are compatible with this one
|
|
(i.e. that operate on the same underlying bitmap). This list must
|
|
be transitive and symmetric; if one context type is defined as
|
|
compatible with another, then all types it is compatible with must
|
|
be compatible with all types the other is compatible with.</p></dd>
|
|
|
|
</dl><p>Vendors may also define experimental contexts using the syntax
|
|
<code><var title="">vendorname</var>-<var title="">context</var></code>, for example,
|
|
<code>moz-3d</code>. Such contexts should be registered in the
|
|
WHATWG Wiki CanvasContexts page.</p>
|
|
|
|
</div><hr><dl class="domintro"><dt><var title="">url</var> = <var title="">canvas</var> . <code title="dom-canvas-toDataURL"><a href="#dom-canvas-todataurl">toDataURL</a></code>( [ <var title="">type</var>, ... ])</dt>
|
|
|
|
<dd>
|
|
|
|
<p>Returns a <a href="infrastructure.html#data-protocol" title="data protocol"><code title="">data:</code> URL</a> for the image in the canvas.</p>
|
|
|
|
<p>The first argument, if provided, controls the type of the image
|
|
to be returned (e.g. PNG or JPEG). The default is <code title="">image/png</code>; that type is also used if the given
|
|
type isn't supported. The other arguments are specific to the
|
|
type, and control the way that the image is generated, as given in
|
|
the table below.</p>
|
|
|
|
<p>When trying to use types other than "<code>image/png</code>",
|
|
authors can check if the image was really returned in the
|
|
requested format by checking to see if the returned string starts
|
|
with one of the exact strings "<code title="">data:image/png,</code>" or "<code title="">data:image/png;</code>". If it does, the image is PNG,
|
|
and thus the requested type was not supported. (The one exception
|
|
to this is if the canvas has either no height or no width, in
|
|
which case the result might simply be "<code title="">data:,</code>".)</p>
|
|
|
|
</dd>
|
|
|
|
<dt><var title="">canvas</var> . <code title="dom-canvas-toBlob"><a href="#dom-canvas-toblob">toBlob</a></code>(<var title="">callback</var> [, <var title="">type</var>, ... ])</dt>
|
|
|
|
<dd>
|
|
|
|
<p>Creates a <code><a href="infrastructure.html#blob">Blob</a></code> object representing a file
|
|
containing the image in the canvas, and invokes a callback with a
|
|
handle to that object.</p>
|
|
|
|
<p>The second argument, if provided, controls the type of the
|
|
image to be returned (e.g. PNG or JPEG). The default is <code title="">image/png</code>; that type is also used if the given
|
|
type isn't supported. The other arguments are specific to the
|
|
type, and control the way that the image is generated, as given in
|
|
the table below.</p>
|
|
|
|
</dd>
|
|
|
|
</dl><div class="impl">
|
|
|
|
<p>The <dfn id="dom-canvas-todataurl" title="dom-canvas-toDataURL"><code>toDataURL()</code></dfn> method
|
|
must run the following steps:</p>
|
|
|
|
<ol><li><p>If the canvas has no pixels (i.e. either its horizontal
|
|
dimension or its vertical dimension is zero) then return the string
|
|
"<code title="">data:,</code>" and abort these steps. (This is the
|
|
shortest <a href="infrastructure.html#data-protocol" title="data protocol"><code title="">data:</code>
|
|
URL</a>; it represents the empty string in a <code title="">text/plain</code> resource.)</p></li>
|
|
|
|
<li><p>Let <var title="">file</var> be <a href="#a-serialization-of-the-image-as-a-file">a serialization of the
|
|
image as a file</a>, using the method's arguments (if any) as
|
|
the <var title="">arguments</var>.</p></li>
|
|
|
|
<li><p>Return a <a href="infrastructure.html#data-protocol" title="data protocol"><code title="">data:</code> URL</a> representing <var title="">file</var>. <a href="references.html#refsRFC2397">[RFC2397]</a></p>
|
|
|
|
|
|
</li></ol><p>The <dfn id="dom-canvas-toblob" title="dom-canvas-toBlob"><code>toBlob()</code></dfn> method
|
|
must run the following steps:</p>
|
|
|
|
<ol><li><p>Let <var title="">callback</var> be the first
|
|
argument.</p></li>
|
|
|
|
<li><p>Let <var title="">arguments</var> be the second and
|
|
subsequent arguments to the method, if any.</p></li>
|
|
|
|
<li><p>Let <var title="">file</var> be <a href="#a-serialization-of-the-image-as-a-file">a serialization of the
|
|
image as a file</a>, using <var title="">arguments</var>.</p></li>
|
|
|
|
<li><p>Return, but continue running these steps
|
|
asynchronously.</p></li>
|
|
|
|
<li><p>If <var title="">callback</var> is null, abort these
|
|
steps.</p></li>
|
|
|
|
<li><p><a href="webappapis.html#queue-a-task">Queue a task</a> to invoke the
|
|
<code>FileCallback</code> <var title="">callback</var> with a
|
|
<code><a href="infrastructure.html#blob">Blob</a></code> object representing <var title="">file</var> as
|
|
its argument. The <a href="webappapis.html#task-source">task source</a> for this task is the
|
|
<dfn id="canvas-blob-serialization-task-source">canvas blob serialization task source</dfn>. <a href="references.html#refsFILESYSTEMAPI">[FILESYSTEMAPI]</a> <a href="references.html#refsFILEAPI">[FILEAPI]</a> </p></li>
|
|
|
|
</ol><p>When a user agent is to create <dfn id="a-serialization-of-the-image-as-a-file">a serialization of the image
|
|
as a file</dfn>, optionally with some given <var title="">arguments</var>, it must create an image file in the format
|
|
given by the first value of <var title="">arguments</var>, or, if
|
|
there are no <var title="">arguments</var>, in the PNG format. <a href="references.html#refsPNG">[PNG]</a></p>
|
|
|
|
<p>If <var title="">arguments</var> is not empty, the first value
|
|
must be interpreted as a <a href="infrastructure.html#mime-type" title="MIME type">MIME type</a>
|
|
giving the format to use. If the type has any parameters, it must be
|
|
treated as not supported.</p>
|
|
|
|
<p class="example">For example, the value "<code>image/png</code>" would
|
|
mean to generate a PNG image, the value "<code>image/jpeg</code>"
|
|
would mean to generate a JPEG image, and the value
|
|
"<code>image/svg+xml</code>" would mean to generate an SVG image
|
|
(which would probably require that the implementation actually keep
|
|
enough information to reliably render an SVG image from the canvas).</p>
|
|
|
|
<p>User agents must support PNG ("<code>image/png</code>"). User
|
|
agents may support other types. If the user agent does not support
|
|
the requested type, it must create the file using the PNG format. <a href="references.html#refsPNG">[PNG]</a></p>
|
|
|
|
<p>User agents must <a href="infrastructure.html#converted-to-ascii-lowercase" title="converted to ASCII
|
|
lowercase">convert the provided type to ASCII lowercase</a>
|
|
before establishing if they support that type.</p>
|
|
|
|
<p>For image types that do not support an alpha channel, the
|
|
serialized image must be the canvas image composited onto a solid
|
|
black background using the source-over operator.</p>
|
|
|
|
<p>If the first argument in <var title="">arguments</var> gives a
|
|
type corresponding to one of the types given in the first column of
|
|
the following table, and the user agent supports that type, then the
|
|
subsequent arguments, if any, must be treated as described in the
|
|
second cell of that row.</p>
|
|
|
|
</div><table><thead><tr><th> Type </th><th> Other arguments </th><th> Reference
|
|
</th></tr></thead><tbody><tr><td> <code>image/jpeg</code>
|
|
</td><td> The second argument<span class="impl">, if it</span> is a
|
|
number in the range 0.0 to 1.0 inclusive<span class="impl">, must
|
|
be</span> treated as the desired quality level. <span class="impl">If it is not a number or is outside that range, the
|
|
user agent must use its default value, as if the argument had
|
|
been omitted.</span>
|
|
</td><td> <a href="references.html#refsJPEG">[JPEG]</a>
|
|
</td></tr></tbody></table><div class="impl">
|
|
|
|
<p>For the purposes of these rules, an argument is considered to be
|
|
a number if it is converted to an IDL double value by the rules for
|
|
handling arguments of type <code title="">any</code> in the Web IDL
|
|
specification. <a href="references.html#refsWEBIDL">[WEBIDL]</a></p>
|
|
|
|
<p>Other arguments must be ignored and must not cause the user agent
|
|
to raise an exception. A future version of this specification will
|
|
probably define other parameters to be passed to these methods to
|
|
allow authors to more carefully control compression settings, image
|
|
metadata, etc.</p>
|
|
|
|
</div><div class="impl">
|
|
|
|
<h5 id="color-spaces-and-color-correction"><span class="secno">4.8.11.1 </span>Color spaces and color correction</h5>
|
|
|
|
<p>The <code><a href="#the-canvas-element">canvas</a></code> APIs must perform color correction at
|
|
only two points: when rendering images with their own gamma
|
|
correction and color space information onto the canvas, to convert
|
|
the image to the color space used by the canvas (e.g. using the 2D
|
|
Context's <code title="dom-context-2d-drawImage">drawImage()</code>
|
|
method with an <code><a href="embedded-content-1.html#htmlimageelement">HTMLImageElement</a></code> object), and when
|
|
rendering the actual canvas bitmap to the output device.</p>
|
|
|
|
<p class="note">Thus, in the 2D context, colors used to draw shapes
|
|
onto the canvas will exactly match colors obtained through the <code title="dom-context-2d-getImageData">getImageData()</code>
|
|
method.</p>
|
|
|
|
<p>The <code title="dom-canvas-toDataURL"><a href="#dom-canvas-todataurl">toDataURL()</a></code> method
|
|
must not include color space information in the resource
|
|
returned. Where the output format allows it, the color of pixels in
|
|
resources created by <code title="dom-canvas-toDataURL"><a href="#dom-canvas-todataurl">toDataURL()</a></code> must match those
|
|
returned by the <code title="dom-context-2d-getImageData">getImageData()</code>
|
|
method.</p>
|
|
|
|
<p>In user agents that support CSS, the color space used by a
|
|
<code><a href="#the-canvas-element">canvas</a></code> element must match the color space used for
|
|
processing any colors for that element in CSS.</p>
|
|
|
|
<p>The gamma correction and color space information of images must
|
|
be handled in such a way that an image rendered directly using an
|
|
<code><a href="embedded-content-1.html#the-img-element">img</a></code> element would use the same colors as one painted on
|
|
a <code><a href="#the-canvas-element">canvas</a></code> element that is then itself
|
|
rendered. Furthermore, the rendering of images that have no color
|
|
correction information (such as those returned by the <code title="dom-canvas-toDataURL"><a href="#dom-canvas-todataurl">toDataURL()</a></code> method) must be
|
|
rendered with no color correction.</p>
|
|
|
|
<p class="note">Thus, in the 2D context, calling the <code title="dom-context-2d-drawImage">drawImage()</code> method to render
|
|
the output of the <code title="dom-canvas-toDataURL"><a href="#dom-canvas-todataurl">toDataURL()</a></code> method to the
|
|
canvas, given the appropriate dimensions, has no visible effect.</p>
|
|
|
|
</div><div class="impl">
|
|
|
|
<h5 id="security-with-canvas-elements"><span class="secno">4.8.11.2 </span>Security with <code><a href="#the-canvas-element">canvas</a></code> elements</h5>
|
|
|
|
<p><strong>Information leakage</strong> can occur if scripts from
|
|
one <a href="origin-0.html#origin">origin</a> can access information (e.g. read pixels)
|
|
from images from another origin (one that isn't the <a href="origin-0.html#same-origin" title="same origin">same</a>).</p>
|
|
|
|
<p>To mitigate this, <code><a href="#the-canvas-element">canvas</a></code> elements are defined to
|
|
have a flag indicating whether they are <i>origin-clean</i>. All
|
|
<code><a href="#the-canvas-element">canvas</a></code> elements must start with their
|
|
<i>origin-clean</i> set to true. The flag must be set to false if
|
|
any of the following actions occur:</p>
|
|
|
|
<ul><li><p>The element's 2D context's <code title="dom-context-2d-drawImage">drawImage()</code> method is
|
|
called with an <code><a href="embedded-content-1.html#htmlimageelement">HTMLImageElement</a></code> or an
|
|
<code><a href="the-iframe-element.html#htmlvideoelement">HTMLVideoElement</a></code> whose <a href="origin-0.html#origin">origin</a> is not the
|
|
<a href="origin-0.html#same-origin" title="same origin">same</a> as that of the
|
|
<code><a href="infrastructure.html#document">Document</a></code> object that owns the <code><a href="#the-canvas-element">canvas</a></code>
|
|
element.</p></li>
|
|
|
|
<li><p>The element's 2D context's <code title="dom-context-2d-drawImage">drawImage()</code> method is
|
|
called with an <code><a href="#htmlcanvaselement">HTMLCanvasElement</a></code> whose
|
|
<i>origin-clean</i> flag is false.</p></li>
|
|
|
|
<li><p>The element's 2D context's <code title="dom-context-2d-fillStyle">fillStyle</code> attribute is set
|
|
to a <code>CanvasPattern</code> object that was created from an
|
|
<code><a href="embedded-content-1.html#htmlimageelement">HTMLImageElement</a></code> or an <code><a href="the-iframe-element.html#htmlvideoelement">HTMLVideoElement</a></code>
|
|
whose <a href="origin-0.html#origin">origin</a> was not the <a href="origin-0.html#same-origin" title="same
|
|
origin">same</a> as that of the <code><a href="infrastructure.html#document">Document</a></code> object
|
|
that owns the <code><a href="#the-canvas-element">canvas</a></code> element when the pattern was
|
|
created.</p></li>
|
|
|
|
<li><p>The element's 2D context's <code title="dom-context-2d-fillStyle">fillStyle</code> attribute is set
|
|
to a <code>CanvasPattern</code> object that was created from an
|
|
<code><a href="#htmlcanvaselement">HTMLCanvasElement</a></code> whose <i>origin-clean</i> flag was
|
|
false when the pattern was created.</p></li>
|
|
|
|
<li><p>The element's 2D context's <code title="dom-context-2d-strokeStyle">strokeStyle</code> attribute is
|
|
set to a <code>CanvasPattern</code> object that was created from an
|
|
<code><a href="embedded-content-1.html#htmlimageelement">HTMLImageElement</a></code> or an <code><a href="the-iframe-element.html#htmlvideoelement">HTMLVideoElement</a></code>
|
|
whose <a href="origin-0.html#origin">origin</a> was not the <a href="origin-0.html#same-origin" title="same
|
|
origin">same</a> as that of the <code><a href="infrastructure.html#document">Document</a></code> object
|
|
that owns the <code><a href="#the-canvas-element">canvas</a></code> element when the pattern was
|
|
created.</p></li>
|
|
|
|
<li><p>The element's 2D context's <code title="dom-context-2d-strokeStyle">strokeStyle</code> attribute is
|
|
set to a <code>CanvasPattern</code> object that was created from an
|
|
<code><a href="#htmlcanvaselement">HTMLCanvasElement</a></code> whose <i>origin-clean</i> flag was
|
|
false when the pattern was created.</p></li>
|
|
|
|
<li><p>The element's 2D context's <code title="dom-context-2d-fillText">fillText()</code> or <code title="dom-context-2d-fillText">strokeText()</code> methods are
|
|
invoked and consider using a font that has an <a href="origin-0.html#origin">origin</a>
|
|
that is not the <a href="origin-0.html#same-origin" title="same origin">same</a> as that of
|
|
the <code><a href="infrastructure.html#document">Document</a></code> object that owns the <code><a href="#the-canvas-element">canvas</a></code>
|
|
element. (The font doesn't even have to be used; all that matters
|
|
is whether the font was considered for any of the glyphs
|
|
drawn.)</p></li>
|
|
</ul><p>Whenever the <code title="dom-canvas-toDataURL"><a href="#dom-canvas-todataurl">toDataURL()</a></code> method of a
|
|
<code><a href="#the-canvas-element">canvas</a></code> element whose <i>origin-clean</i> flag is set to
|
|
false is called, the method must raise a <code><a href="common-dom-interfaces.html#security_err">SECURITY_ERR</a></code>
|
|
exception.</p>
|
|
|
|
<p>Whenever the <code title="dom-context-2d-getImageData">getImageData()</code> method of
|
|
the 2D context of a <code><a href="#the-canvas-element">canvas</a></code> element whose
|
|
<i>origin-clean</i> flag is set to false is called with otherwise
|
|
correct arguments, the method must raise a <code><a href="common-dom-interfaces.html#security_err">SECURITY_ERR</a></code>
|
|
exception.</p>
|
|
|
|
<p>Whenever the <code title="dom-context-2d-measureText">measureText()</code> method of
|
|
the 2D context of a <code><a href="#the-canvas-element">canvas</a></code> element ends up using a font
|
|
that has an <a href="origin-0.html#origin">origin</a> that is not the <a href="origin-0.html#same-origin" title="same
|
|
origin">same</a> as that of the <code><a href="infrastructure.html#document">Document</a></code> object that
|
|
owns the <code><a href="#the-canvas-element">canvas</a></code> element, the method must raise a
|
|
<code><a href="common-dom-interfaces.html#security_err">SECURITY_ERR</a></code> exception.</p>
|
|
|
|
<p class="note">Even resetting the canvas state by changing its
|
|
<code title="attr-canvas-width"><a href="#attr-canvas-width">width</a></code> or <code title="attr-canvas-height"><a href="#attr-canvas-height">height</a></code> attributes doesn't reset
|
|
the <i>origin-clean</i> flag.</p>
|
|
|
|
</div></body></html>
|