Javascript 如何在HTML画布上找到文本的高度？
该规范有一个context.measureText（text）函数，它会告诉您打印该文本需要多少宽度，但我找不到一种方法来确定它有多高。我知道它是基于字体的，但我不知道如何将字体字符串转换为文本高度。画布规范没有为我们提供测量字符串高度的方法。但是，您可以以像素为单位设置文本的大小，并且通常可以相对轻松地确定垂直边界 如果您需要更精确的内容，那么您可以将文本扔到画布上，然后获取像素数据并计算垂直使用的像素数。这将相对简单，但效率不高。您可以这样做（它可以工作，但会在画布上绘制一些要删除的文本）：Javascript 如何在HTML画布上找到文本的高度？,javascript,text,canvas,Javascript,Text,Canvas,该规范有一个context.measureText（text）函数，它会告诉您打印该文本需要多少宽度，但我找不到一种方法来确定它有多高。我知道它是基于字体的，但我不知道如何将字体字符串转换为文本高度。画布规范没有为我们提供测量字符串高度的方法。但是，您可以以像素为单位设置文本的大小，并且通常可以相对轻松地确定垂直边界 如果您需要更精确的内容，那么您可以将文本扔到画布上，然后获取像素数据并计算垂直使用的像素数。这将相对简单，但效率不高。您可以这样做（它可以工作，但会在画布上绘制一些要删除的文本）：
但是，设置字体大小可能并不实用，因为 ctx.font=“”
将使用CSS定义的字体以及任何嵌入的字体标记。如果你使用CSS字体，你根本不知道从编程的角度来说，使用measureText方法的高度是多少，这是非常短视的。另一方面，IE8确实返回了宽度和高度。编辑：是否使用画布变换？如果是，则必须跟踪变换矩阵。以下方法应使用初始变换测量文本的高度 编辑#2：奇怪的是，当我在这个StackOverflow页面上运行下面的代码时，它并没有生成正确的答案；某些样式规则的存在完全可能会破坏此功能 画布使用CSS定义的字体，因此理论上，我们可以向文档中添加一个适当样式的文本块，并测量其高度。我认为这比渲染文本然后检查像素数据要容易得多，而且还应该考虑上升和下降。请查看以下内容：
var determineFontHeight = function(fontStyle) {
var body = document.getElementsByTagName("body")[0];
var dummy = document.createElement("div");
var dummyText = document.createTextNode("M");
dummy.appendChild(dummyText);
dummy.setAttribute("style", fontStyle);
body.appendChild(dummy);
var result = dummy.offsetHeight;
body.removeChild(dummy);
return result;
};
//A little test...
var exampleFamilies = ["Helvetica", "Verdana", "Times New Roman", "Courier New"];
var exampleSizes = [8, 10, 12, 16, 24, 36, 48, 96];
for(var i = 0; i < exampleFamilies.length; i++) {
var family = exampleFamilies[i];
for(var j = 0; j < exampleSizes.length; j++) {
var size = exampleSizes[j] + "pt";
var style = "font-family: " + family + "; font-size: " + size + ";";
var pixelHeight = determineFontHeight(style);
console.log(family + " " + size + " ==> " + pixelHeight + " pixels high.");
}
}
我正在写一个终端模拟器，所以我需要在字符周围画矩形
var size = 10
var lineHeight = 1.2 // CSS "line-height: normal" is between 1 and 1.2
context.font = size+'px/'+lineHeight+'em monospace'
width = context.measureText('m').width
height = size * lineHeight
显然，如果你想要角色占据的确切空间量，这是没有帮助的。但对于某些用途，它会给出一个很好的近似值。有趣的是，TextMetrics只有宽度，没有高度： 你能用这个例子中的跨度吗
更新-作为这项工作的一个例子，我在中使用了这项技术 根据ellisbben的回答，这里是一个增强版，用于从基线获取上升和下降，即与Win32 API返回的
tmastencetmastencevar getTextHeight = function(font) {
var text = $('<span>Hg</span>').css({ fontFamily: font });
var block = $('<div style="display: inline-block; width: 1px; height: 0px;"></div>');
var div = $('<div></div>');
div.append(text, block);
var body = $('body');
body.append(div);
try {
var result = {};
block.css({ verticalAlign: 'baseline' });
result.ascent = block.offset().top - text.offset().top;
block.css({ verticalAlign: 'bottom' });
result.height = block.offset().top - text.offset().top;
result.descent = result.height - result.ascent;
} finally {
div.remove();
}
return result;
};
var font = '36pt Times';
var message = 'Big Text';
ctx.fillStyle = 'black';
ctx.textAlign = 'left';
ctx.textBaseline = 'top'; // important!
ctx.font = font;
ctx.fillText(message, x, y);
// Canvas can tell us the width
var w = ctx.measureText(message).width;
// New function gets the other info we need
var h = getTextHeight(font);
testLine(ctx, x, y, w, 'red');
testLine(ctx, x, y + h.ascent, w, 'green');
testLine(ctx, x, y + h.height, w, 'blue');
正如JJ Stiff所建议的，您可以将文本添加到跨距中，然后测量跨距的偏移
var d = document.createElement("span");
d.font = "20px arial";
d.textContent = "Hello world!";
document.body.appendChild(d);
var emHeight = d.offsetHeight;
document.body.removeChild(d);
如图所示，如果您使用context.font定义字体，文本的高度（以像素为单位）不等于字体大小（以pts为单位）吗？您可以通过检查大写字母M的长度，获得非常接近垂直高度的近似值
ctx.font = 'bold 10px Arial';
lineHeight = ctx.measureText('M').width;
我用像素操作解决了这个问题 以下是图形化的答案： 以下是代码：
function textHeight (text, font) {
var fontDraw = document.createElement("canvas");
var height = 100;
var width = 100;
// here we expect that font size will be less canvas geometry
fontDraw.setAttribute("height", height);
fontDraw.setAttribute("width", width);
var ctx = fontDraw.getContext('2d');
// black is default
ctx.fillRect(0, 0, width, height);
ctx.textBaseline = 'top';
ctx.fillStyle = 'white';
ctx.font = font;
ctx.fillText(text/*'Eg'*/, 0, 0);
var pixels = ctx.getImageData(0, 0, width, height).data;
// row numbers where we first find letter end where it ends
var start = -1;
var end = -1;
for (var row = 0; row < height; row++) {
for (var column = 0; column < width; column++) {
var index = (row * width + column) * 4;
// if pixel is not white (background color)
if (pixels[index] == 0) {
// we havent met white (font color) pixel
// on the row and the letters was detected
if (column == width - 1 && start != -1) {
end = row;
row = height;
break;
}
continue;
}
else {
// we find top of letter
if (start == -1) {
start = row;
}
// ..letters body
break;
}
}
}
/*
document.body.appendChild(fontDraw);
fontDraw.style.pixelLeft = 400;
fontDraw.style.pixelTop = 400;
fontDraw.style.position = "absolute";
*/
return end - start;
}
函数文本高度（文本、字体）{
var fontDraw=document.createElement（“画布”）；
var高度=100；
var宽度=100；
//在这里，我们预计字体大小将小于画布几何体
setAttribute（“高度”，高度）；
setAttribute（“宽度”，宽度）；
var ctx=fontDraw.getContext（'2d'）；
//默认为黑色
ctx.fillRect（0，0，宽度，高度）；
ctx.textb基线='top'；
ctx.fillStyle='白色'；
ctx.font=font；
ctx.fillText（text/*'Eg'*/，0,0）；
var pixels=ctx.getImageData（0，0，宽度，高度）；
//我们第一次发现字母结尾的行号
var start=-1；
var-end=-1；
对于（变量行=0；行<高度；行++）{
用于（变量列=0；列<宽度；列++）{
var指数=（行*宽+列）*4；
//如果像素不是白色（背景色）
如果（像素[索引]==0）{
//我们还没有遇到白色（字体颜色）像素
//在该行中，已检测到这些字母
如果（列==宽度-1&&start！=-1）{
结束=行；
行=高度；
打破
}
继续；
}
否则{
//我们找到了信的开头
如果（开始==-1）{
开始=行；
}
//…信函正文
打破
}
}
}
/*
document.body.appendChild（fontDraw）；
fontDraw.style.pixelLeft=400；
fontDraw.style.pixelTop=400；
fontDraw.style.position=“绝对”；
*/
返回结束-开始；
}
context.font = "22px arial";
context.measureText(string).width
如果您使用的测量值不是px，那么高度仍然是相同的，但是使用该测量值，您最多只需转换测量值。只需添加Daniel的答案（这很好！绝对正确！），没有JQuery的版本：
function objOff(obj)
{
var currleft = currtop = 0;
if( obj.offsetParent )
{ do { currleft += obj.offsetLeft; currtop += obj.offsetTop; }
while( obj = obj.offsetParent ); }
else { currleft += obj.offsetLeft; currtop += obj.offsetTop; }
return [currleft,currtop];
}
function FontMetric(fontName,fontSize)
{
var text = document.createElement("span");
text.style.fontFamily = fontName;
text.style.fontSize = fontSize + "px";
text.innerHTML = "ABCjgq|";
// if you will use some weird fonts, like handwriting or symbols, then you need to edit this test string for chars that will have most extreme accend/descend values
var block = document.createElement("div");
block.style.display = "inline-block";
block.style.width = "1px";
block.style.height = "0px";
var div = document.createElement("div");
div.appendChild(text);
div.appendChild(block);
// this test div must be visible otherwise offsetLeft/offsetTop will return 0
// but still let's try to avoid any potential glitches in various browsers
// by making it's height 0px, and overflow hidden
div.style.height = "0px";
div.style.overflow = "hidden";
// I tried without adding it to body - won't work. So we gotta do this one.
document.body.appendChild(div);
block.style.verticalAlign = "baseline";
var bp = objOff(block);
var tp = objOff(text);
var taccent = bp[1] - tp[1];
block.style.verticalAlign = "bottom";
bp = objOff(block);
tp = objOff(text);
var theight = bp[1] - tp[1];
var tdescent = theight - taccent;
// now take it off :-)
document.body.removeChild(div);
// return text accent, descent and total height
return [taccent,theight,tdescent];
}
function textHeight (text, font) {
var fontDraw = document.createElement("canvas");
var height = 100;
var width = 100;
// here we expect that font size will be less canvas geometry
fontDraw.setAttribute("height", height);
fontDraw.setAttribute("width", width);
var ctx = fontDraw.getContext('2d');
// black is default
ctx.fillRect(0, 0, width, height);
ctx.textBaseline = 'top';
ctx.fillStyle = 'white';
ctx.font = font;
ctx.fillText(text/*'Eg'*/, 0, 0);
var pixels = ctx.getImageData(0, 0, width, height).data;
// row numbers where we first find letter end where it ends
var start = -1;
var end = -1;
for (var row = 0; row < height; row++) {
for (var column = 0; column < width; column++) {
var index = (row * width + column) * 4;
// if pixel is not white (background color)
if (pixels[index] == 0) {
// we havent met white (font color) pixel
// on the row and the letters was detected
if (column == width - 1 && start != -1) {
end = row;
row = height;
break;
}
continue;
}
else {
// we find top of letter
if (start == -1) {
start = row;
}
// ..letters body
break;
}
}
}
/*
document.body.appendChild(fontDraw);
fontDraw.style.pixelLeft = 400;
fontDraw.style.pixelTop = 400;
fontDraw.style.position = "absolute";
*/
return end - start;
}
context.font = "22px arial";
context.measureText(string).width
function objOff(obj)
{
var currleft = currtop = 0;
if( obj.offsetParent )
{ do { currleft += obj.offsetLeft; currtop += obj.offsetTop; }
while( obj = obj.offsetParent ); }
else { currleft += obj.offsetLeft; currtop += obj.offsetTop; }
return [currleft,currtop];
}
function FontMetric(fontName,fontSize)
{
var text = document.createElement("span");
text.style.fontFamily = fontName;
text.style.fontSize = fontSize + "px";
text.innerHTML = "ABCjgq|";
// if you will use some weird fonts, like handwriting or symbols, then you need to edit this test string for chars that will have most extreme accend/descend values
var block = document.createElement("div");
block.style.display = "inline-block";
block.style.width = "1px";
block.style.height = "0px";
var div = document.createElement("div");
div.appendChild(text);
div.appendChild(block);
// this test div must be visible otherwise offsetLeft/offsetTop will return 0
// but still let's try to avoid any potential glitches in various browsers
// by making it's height 0px, and overflow hidden
div.style.height = "0px";
div.style.overflow = "hidden";
// I tried without adding it to body - won't work. So we gotta do this one.
document.body.appendChild(div);
block.style.verticalAlign = "baseline";
var bp = objOff(block);
var tp = objOff(text);
var taccent = bp[1] - tp[1];
block.style.verticalAlign = "bottom";
bp = objOff(block);
tp = objOff(text);
var theight = bp[1] - tp[1];
var tdescent = theight - taccent;
// now take it off :-)
document.body.removeChild(div);
// return text accent, descent and total height
return [taccent,theight,tdescent];
}
var can = CanvasElement.getContext('2d'); //get context
var lineHeight = /[0-9]+(?=pt|px)/.exec(can.font); //get height from font variable
alert(measureHeight('40px serif', 40, 'rg').height)
function measureHeight(aFont, aSize, aChars, aOptions={}) {
// if you do pass aOptions.ctx, keep in mind that the ctx properties will be changed and not set back. so you should have a devoted canvas for this
// if you dont pass in a width to aOptions, it will return it to you in the return object
// the returned width is Math.ceil'ed
console.error('aChars: "' + aChars + '"');
var defaultOptions = {
width: undefined, // if you specify a width then i wont have to use measureText to get the width
canAndCtx: undefined, // set it to object {can:,ctx:} // if not provided, i will make one
range: 3
};
aOptions.range = aOptions.range || 3; // multiples the aSize by this much
if (aChars === '') {
// no characters, so obviously everything is 0
return {
relativeBot: 0,
relativeTop: 0,
height: 0,
width: 0
};
// otherwise i will get IndexSizeError: Index or size is negative or greater than the allowed amount error somewhere below
}
// validateOptionsObj(aOptions, defaultOptions); // not needed because all defaults are undefined
var can;
var ctx;
if (!aOptions.canAndCtx) {
can = document.createElement('canvas');;
can.mozOpaque = 'true'; // improved performanceo on firefox i guess
ctx = can.getContext('2d');
// can.style.position = 'absolute';
// can.style.zIndex = 10000;
// can.style.left = 0;
// can.style.top = 0;
// document.body.appendChild(can);
} else {
can = aOptions.canAndCtx.can;
ctx = aOptions.canAndCtx.ctx;
}
var w = aOptions.width;
if (!w) {
ctx.textBaseline = 'alphabetic';
ctx.textAlign = 'left';
ctx.font = aFont;
w = ctx.measureText(aChars).width;
}
w = Math.ceil(w); // needed as i use w in the calc for the loop, it needs to be a whole number
// must set width/height, as it wont paint outside of the bounds
can.width = w;
can.height = aSize * aOptions.range;
ctx.font = aFont; // need to set the .font again, because after changing width/height it makes it forget for some reason
ctx.textBaseline = 'alphabetic';
ctx.textAlign = 'left';
ctx.fillStyle = 'white';
console.log('w:', w);
var avgOfRange = (aOptions.range + 1) / 2;
var yBaseline = Math.ceil(aSize * avgOfRange);
console.log('yBaseline:', yBaseline);
ctx.fillText(aChars, 0, yBaseline);
var yEnd = aSize * aOptions.range;
var data = ctx.getImageData(0, 0, w, yEnd).data;
// console.log('data:', data)
var botBound = -1;
var topBound = -1;
// measureHeightY:
for (y=0; y<=yEnd; y++) {
for (var x = 0; x < w; x += 1) {
var n = 4 * (w * y + x);
var r = data[n];
var g = data[n + 1];
var b = data[n + 2];
// var a = data[n + 3];
if (r+g+b > 0) { // non black px found
if (topBound == -1) {
topBound = y;
}
botBound = y; // break measureHeightY; // dont break measureHeightY ever, keep going, we till yEnd. so we get proper height for strings like "`." or ":" or "!"
break;
}
}
}
return {
relativeBot: botBound - yBaseline, // relative to baseline of 0 // bottom most row having non-black
relativeTop: topBound - yBaseline, // relative to baseline of 0 // top most row having non-black
height: (botBound - topBound) + 1,
width: w// EDIT: comma has been added to fix old broken code.
};
}
AutoWrappedText.auto_wrap = function(ctx, text, maxWidth, maxHeight) {
var words = text.split("");
var lines = [];
var currentLine = words[0];
var total_height = 0;
for (var i = 1; i < words.length; i++) {
var word = words[i];
var width = ctx.measureText(currentLine + word).width;
if (width < maxWidth) {
currentLine += word;
} else {
lines.push(currentLine);
currentLine = word;
// TODO dynamically get font size
total_height += 25;
if (total_height >= maxHeight) {
break
}
}
}
if (total_height + 25 < maxHeight) {
lines.push(currentLine);
} else {
lines[lines.length - 1] += "…";
}
return lines;};
let metrics = ctx.measureText(text);
let fontHeight = metrics.fontBoundingBoxAscent + metrics.fontBoundingBoxDescent;
let actualHeight = metrics.actualBoundingBoxAscent + metrics.actualBoundingBoxDescent;
var height = parseInt(ctx.font) * 1.2;
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.font = "100px Arial";
var txt = "Hello guys!"
var wt = ctx.measureText(txt).width;
var height = wt / txt.length;
<div class="measureText" id="measureText">
</div>
.measureText {
margin: 0;
padding: 0;
border: 0;
font-family: Arial;
position: fixed;
visibility: hidden;
height: auto;
width: auto;
white-space: pre-wrap;
line-height: 100%;
}
function getTextFieldMeasure(fontSize, value) {
const div = document.getElementById("measureText");
// returns wrong result for multiline text with last line empty
let arr = value.split('\n');
if (arr[arr.length-1].length == 0) {
value += '.';
}
div.innerText = value;
div.style['font-size']= fontSize + "px";
let rect = div.getBoundingClientRect();
return {width: rect.width, height: rect.height};
};
var measureTextHeight = function(fontFamily, fontSize)
{
var text = document.createElement('span');
text.style.fontFamily = fontFamily;
text.style.fontSize = fontSize + "px";
text.textContent = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ";
document.body.appendChild(text);
var result = text.getBoundingClientRect().height;
document.body.removeChild(text);
return result;
};
/*
* Monkeypatch CanvasRenderingContext2D.measureText() to include actual height of the text
*/
; (function (global) {
"use strict";
var _measureText = global.CanvasRenderingContext2D.prototype.measureText;
global.CanvasRenderingContext2D.prototype.measureText = function () {
var textMetrics = _measureText.apply(this, arguments);
var _getHeight = function (text) {
var $span = global.document.createElement("span");
var spanTextNode = global.document.createTextNode(text);
$span.appendChild(spanTextNode);
$span.setAttribute("style", `font: ${this.font}`);
var $div = global.document.createElement("div");
$div.setAttribute("style", "display: inline-block; width: 1px; height: 0; vertical-align: super;");
var $parentDiv = global.document.createElement("div");
$parentDiv.appendChild($span);
$parentDiv.appendChild($div);
var $body = global.document.getElementsByTagName("body")[0];
$body.appendChild($parentDiv);
var divRect = $div.getBoundingClientRect();
var spanRect = $span.getBoundingClientRect();
var result = {};
$div.style.verticalAlign = "baseline";
result.ascent = divRect.top - spanRect.top;
$div.style.verticalAlign = "bottom";
result.height = divRect.top - spanRect.top;
result.descent = result.height - result.ascent;
$body.removeChild($parentDiv);
return result.height - result.descent;
}.bind(this);
var height = _getHeight(arguments[0]);
global.Object.defineProperty(textMetrics, "height", { value: height });
return textMetrics;
};
})(window);
ctx.font = "bold 64px Verdana, sans-serif"; // Automatically considers it as part of height calculation
var textMetrics = ctx.measureText("Foobar");
var textHeight = textMetrics.height;