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mrdoob/html2canvas.js

Created March 9, 2020 23:36
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Paints a HTML node into a <canvas> (Very basic CSS support)
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html2canvas.js
/**
* @author mrdoob / http://mrdoob.com/
*/
function html2canvas( element ) {
var range = document.createRange();
function Clipper( context ) {
var clips = [];
var isClipping = false;
function doClip() {
if ( isClipping ) {
isClipping = false;
context.restore();
}
if ( clips.length === 0 ) return;
var minX = - Infinity, minY = - Infinity;
var maxX = Infinity, maxY = Infinity;
for ( var i = 0; i < clips.length; i ++ ) {
var clip = clips[ i ];
minX = Math.max( minX, clip.x );
minY = Math.max( minY, clip.y );
maxX = Math.min( maxX, clip.x + clip.width );
maxY = Math.min( maxY, clip.y + clip.height );
}
context.save();
context.beginPath();
context.rect( minX, minY, maxX - minX, maxY - minY );
context.clip();
isClipping = true;
}
return {
add: function ( clip ) {
clips.push( clip );
doClip();
},
remove: function () {
clips.pop();
doClip();
}
};
}
function drawText( style, x, y, string ) {
if ( string !== '' ) {
context.font = style.fontSize + ' ' + style.fontFamily;
context.textBaseline = 'top';
context.fillStyle = style.color;
context.fillText( string, x, y );
}
}
function drawBorder( style, which, x, y, width, height ) {
var borderWidth = style[ which + 'Width' ];
var borderStyle = style[ which + 'Style' ];
var borderColor = style[ which + 'Color' ];
if ( borderWidth !== '0px' && borderStyle !== 'none' && borderColor !== 'transparent' && borderColor !== 'rgba(0, 0, 0, 0)' ) {
context.strokeStyle = borderColor;
context.beginPath();
context.moveTo( x, y );
context.lineTo( x + width, y + height );
context.stroke();
}
}
function drawElement( element, style ) {
var x = 0, y = 0, width = 0, height = 0;
if ( element.nodeType === 3 ) {
// text
range.selectNode( element );
var rect = range.getBoundingClientRect();
x = rect.left - offset.left - 0.5;
y = rect.top - offset.top - 0.5;
width = rect.width;
height = rect.height;
drawText( style, x, y, element.nodeValue.trim() );
} else {
if ( element.style.display === 'none' ) return;
var rect = element.getBoundingClientRect();
x = rect.left - offset.left - 0.5;
y = rect.top - offset.top - 0.5;
width = rect.width;
height = rect.height;
style = window.getComputedStyle( element );
var backgroundColor = style.backgroundColor;
if ( backgroundColor !== 'transparent' && backgroundColor !== 'rgba(0, 0, 0, 0)' ) {
context.fillStyle = backgroundColor;
context.fillRect( x, y, width, height );
}
drawBorder( style, 'borderTop', x, y, width, 0 );
drawBorder( style, 'borderLeft', x, y, 0, height );
drawBorder( style, 'borderBottom', x, y + height, width, 0 );
drawBorder( style, 'borderRight', x + width, y, 0, height );
if ( element.type === 'color' || element.type === 'text' ) {
clipper.add( { x: x, y: y, width: width, height: height } );
drawText( style, x + parseInt( style.paddingLeft ), y + parseInt( style.paddingTop ), element.value );
clipper.remove();
}
}
/*
// debug
context.strokeStyle = '#' + Math.random().toString( 16 ).slice( - 3 );
context.strokeRect( x - 0.5, y - 0.5, width + 1, height + 1 );
*/
var isClipping = style.overflow === 'auto' || style.overflow === 'hidden';
if ( isClipping ) clipper.add( { x: x, y: y, width: width, height: height } );
for ( var i = 0; i < element.childNodes.length; i ++ ) {
drawElement( element.childNodes[ i ], style );
}
if ( isClipping ) clipper.remove();
}
var offset = element.getBoundingClientRect();
var canvas = document.createElement( 'canvas' );
canvas.width = offset.width;
canvas.height = offset.height;
var context = canvas.getContext( '2d'/*, { alpha: false }*/ );
var clipper = new Clipper( context );
console.time( 'drawElement' );
drawElement( element );
console.timeEnd( 'drawElement' );
return canvas;
}
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