我正在尝试做一些应该非常简单的事情，但我在失败和论坛之间度过了我的一天..
我想调整我的字体以匹配我的基线。 在 indesign 上它是一次点击，但在 css 中它看起来像是世界上最困难的事情..
让我们举一个有理数的简单例子。
在这张图片上，我每隔 20 像素就有一个基线。
所以对于我的 <body>我这样做:
<style>
body {font-size:16px; line-height:20px;}
</style>
一切正常。我的段落与基线相符。
但是当我编写我的 <h> 脚本时那不再符合基线了..我做错了什么？那应该遵循我的基线，不是吗？
<style type="text/css">
body{font-size: 16px; line-height: 20px;}
h1{font-size: 5em; line-height: 1.25em;}
h2{font-size: 4em; line-height: 1.25em;}
h3{font-size: 3em; line-height: 1.25em;}
h4{font-size: 2em; line-height: 1.25em;}
</style>
ps: 20/16=1.25em
在我的检查器中，计算返回预期值
h1{font-size: 84px; line-height: 100px;}
h2{font-size: 68px; line-height: 80px;}
h3{font-size: 52px; line-height: 60px;}
h4{font-size: 36px; line-height: 40px;}
所以应该显示类似这样的东西不是吗？ 
最佳答案
这有点复杂 - 你必须先测量字体(就像 InDesign 所做的那样)并计算“行高”，你称之为“bottom_gap”的东西和其他一些东西
I'm pretty sure we can do something in JavaScript..
你是对的——但对于排版，JS 用于计算 CSS(取决于字体指标)
在这里演示了第一步(测量字体) https://codepen.io/sebilasse/pen/gPBQqm 它只是以图形方式显示 [对于技术背景] 测量的内容
这种测量是必要的，因为每种字体在“行”中的表现完全不同。
这里有一个生成器可以生成这样的 Typo CSS:
https://codepen.io/sebilasse/pen/BdaPzN
要测量的函数可以基于 <canvas>看起来像这样:
function getMetrics(fontName, fontSize) {
// NOTE: if there is no getComputedStyle, this library won't work.
if(!document.defaultView.getComputedStyle) {
throw("ERROR: 'document.defaultView.getComputedStyle' not found. This library only works in browsers that can report computed CSS values.");
}
if (!document.querySelector('canvas')) {
var _canvas = document.createElement('canvas');
_canvas.width = 220; _canvas.height = 220;
document.body.appendChild(_canvas);
}
// Store the old text metrics function on the Canvas2D prototype
CanvasRenderingContext2D.prototype.measureTextWidth = CanvasRenderingContext2D.prototype.measureText;
/**
* Shortcut function for getting computed CSS values
*/
var getCSSValue = function(element, property) {
return document.defaultView.getComputedStyle(element,null).getPropertyValue(property);
};
/**
* The new text metrics function
*/
CanvasRenderingContext2D.prototype.measureText = function(textstring) {
var metrics = this.measureTextWidth(textstring),
fontFamily = getCSSValue(this.canvas,"font-family"),
fontSize = getCSSValue(this.canvas,"font-size").replace("px",""),
isSpace = !(/\S/.test(textstring));
metrics.fontsize = fontSize;
// For text lead values, we meaure a multiline text container.
var leadDiv = document.createElement("div");
leadDiv.style.position = "absolute";
leadDiv.style.margin = 0;
leadDiv.style.padding = 0;
leadDiv.style.opacity = 0;
leadDiv.style.font = fontSize + "px " + fontFamily;
leadDiv.innerHTML = textstring + "<br/>" + textstring;
document.body.appendChild(leadDiv);
// Make some initial guess at the text leading (using the standard TeX ratio)
metrics.leading = 1.2 * fontSize;
// Try to get the real value from the browser
var leadDivHeight = getCSSValue(leadDiv,"height");
leadDivHeight = leadDivHeight.replace("px","");
if (leadDivHeight >= fontSize * 2) { metrics.leading = (leadDivHeight/2) | 0; }
document.body.removeChild(leadDiv);
// if we're not dealing with white space, we can compute metrics
if (!isSpace) {
// Have characters, so measure the text
var canvas = document.createElement("canvas");
var padding = 100;
canvas.width = metrics.width + padding;
canvas.height = 3*fontSize;
canvas.style.opacity = 1;
canvas.style.fontFamily = fontFamily;
canvas.style.fontSize = fontSize;
var ctx = canvas.getContext("2d");
ctx.font = fontSize + "px " + fontFamily;
var w = canvas.width,
h = canvas.height,
baseline = h/2;
// Set all canvas pixeldata values to 255, with all the content
// data being 0. This lets us scan for data[i] != 255.
ctx.fillStyle = "white";
ctx.fillRect(-1, -1, w+2, h+2);
ctx.fillStyle = "black";
ctx.fillText(textstring, padding/2, baseline);
var pixelData = ctx.getImageData(0, 0, w, h).data;
// canvas pixel data is w*4 by h*4, because R, G, B and A are separate,
// consecutive values in the array, rather than stored as 32 bit ints.
var i = 0,
w4 = w * 4,
len = pixelData.length;
// Finding the ascent uses a normal, forward scanline
while (++i < len && pixelData[i] === 255) {}
var ascent = (i/w4)|0;
// Finding the descent uses a reverse scanline
i = len - 1;
while (--i > 0 && pixelData[i] === 255) {}
var descent = (i/w4)|0;
// find the min-x coordinate
for(i = 0; i<len && pixelData[i] === 255; ) {
i += w4;
if(i>=len) { i = (i-len) + 4; }}
var minx = ((i%w4)/4) | 0;
// find the max-x coordinate
var step = 1;
for(i = len-3; i>=0 && pixelData[i] === 255; ) {
i -= w4;
if(i<0) { i = (len - 3) - (step++)*4; }}
var maxx = ((i%w4)/4) + 1 | 0;
// set font metrics
metrics.ascent = (baseline - ascent);
metrics.descent = (descent - baseline);
metrics.bounds = { minx: minx - (padding/2),
maxx: maxx - (padding/2),
miny: 0,
maxy: descent-ascent };
metrics.height = 1+(descent - ascent);
} else {
// Only whitespace, so we can't measure the text
metrics.ascent = 0;
metrics.descent = 0;
metrics.bounds = { minx: 0,
maxx: metrics.width, // Best guess
miny: 0,
maxy: 0 };
metrics.height = 0;
}
return metrics;
};
注意您还需要一个好的“reset.css”来重置浏览器边距和填充。
你点击“show CSS”，你也可以使用生成的CSS来混合多种字体:
如果它们有不同的基本大小，则将第二个标准化:
var factor = CSS1baseSize / CSS2baseSize;
现在用 CSS2 重新计算每个字体
var size = size * factor;
请参阅 https://codepen.io/sebilasse/pen/oENGev?editors=1100 中的演示
如果涉及图像怎么办？ 下面的演示使用两种具有相同指标的字体加上一个额外的 JS 部分。需要计算基线网格的图像等媒体元素: https://codepen.io/sebilasse/pen/ddopBj
关于html - css 字体大小和行高与基线不匹配，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48447858/