给定 (1) 字体系列和 (2) Unicode 字符代码。
是否有可能在 JavaScript 中生成如下所示的图像：
http://www.freetype.org/freetype2/docs/tutorial/metrics.png
基本上，我想：
- 显示角色本身（放大）
- 获取各种字体指标
- 画一束浅灰色的线条
现在，绘制浅灰色线条很简单——我只使用 SVG。但是，如何提取字符的字体度量？
user1311390
问问题
4763 次
1 回答
6
基于上面提到的库，我制作了这个 codepen
http://codepen.io/sebilasse/pen/gPBQqm?editors=1010
[编辑：capHeight 现在基于H下面@sebdesign 建议的字母]
HTML
<h4>
Change font name
<input value="Maven Pro"></input>
<small>[local or google]</small>
and font size
<input value="40px" size=8></input>
and
<button onclick="getMetrics()">
<strong>get metrics</strong>
</button>
</h4>
<div id="illustrationContainer"></div>
<pre id="log"></pre>
<canvas id="cvs" width="220" height="200"></canvas>
JS
(getMetrics());
function getMetrics() {
var testtext = "Sixty Handgloves ABC";
// 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.");
}
// 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);
};
// debug function
var show = function(canvas, ctx, xstart, w, h, metrics)
{
document.body.appendChild(canvas);
ctx.strokeStyle = 'rgba(0, 0, 0, 0.5)';
ctx.beginPath();
ctx.moveTo(xstart,0);
ctx.lineTo(xstart,h);
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.moveTo(xstart+metrics.bounds.maxx,0);
ctx.lineTo(xstart+metrics.bounds.maxx,h);
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.moveTo(0,h/2-metrics.ascent);
ctx.lineTo(w,h/2-metrics.ascent);
ctx.closePath();
ctx.stroke();
ctx.beginPath();
ctx.moveTo(0,h/2+metrics.descent);
ctx.lineTo(w,h/2+metrics.descent);
ctx.closePath();
ctx.stroke();
}
/**
* 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.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;
// then we 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);
}
// if we ARE dealing with whitespace, most values will just be zero.
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;
};
//callback();
var fontName = document.getElementsByTagName('input')[0].value;
var fontSize = document.getElementsByTagName('input')[1].value;
var WebFontConfig = {
google: {
families: [ [encodeURIComponent(fontName),'::latin'].join('') ]
}
};
var wf = document.createElement('script');
wf.src = ('https:' == document.location.protocol ? 'https' : 'http') +
'://ajax.googleapis.com/ajax/libs/webfont/1/webfont.js';
wf.type = 'text/javascript';
wf.async = 'true';
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(wf, s);
document.body.style.fontFamily = ['"'+fontName+'"', "Arial sans"].join(' ')
var canvas = document.getElementById('cvs'),
context = canvas.getContext("2d");
var w=220, h=200;
canvas.style.font = [fontSize, fontName].join(' ');
context.font = [fontSize, fontName].join(' ');
context.clearRect(0, 0, canvas.width, canvas.height);
// draw bounding box and text
var xHeight = context.measureText("x").height;
var capHeight = context.measureText("H").height;
var metrics = context.measureText("Sxy");
var xStart = (w - metrics.width)/2;
context.fontFamily = fontName;
context.fillStyle = "#FFAF00";
context.fillRect(xStart, h/2-metrics.ascent, metrics.bounds.maxx-metrics.bounds.minx, 1+metrics.bounds.maxy-metrics.bounds.miny);
context.fillStyle = "#333333";
context.fillText(testtext, xStart, h/2);
metrics.fontsize = parseInt(metrics.fontsize);
metrics.offset = Math.ceil((metrics.leading - metrics.height) / 2);
metrics.width = JSON.parse(JSON.stringify(metrics.width));
metrics.capHeight = capHeight;
metrics.xHeight = xHeight - 1;
metrics.ascender = metrics.capHeight - metrics.xHeight;
metrics.descender = metrics.descent;
var myMetrics = {
px: JSON.parse(JSON.stringify(metrics)),
relative: {
fontsize: 1,
offset: (metrics.offset / metrics.fontsize),
height: (metrics.height / metrics.fontsize),
capHeight: (metrics.capHeight / metrics.fontsize),
ascender: (metrics.ascender / metrics.fontsize),
xHeight: (metrics.xHeight / metrics.fontsize),
descender: (metrics.descender / metrics.fontsize)
},
descriptions: {
ascent: 'distance above baseline',
descent: 'distance below baseline',
height: 'ascent + 1 for the baseline + descent',
leading: 'distance between consecutive baselines',
bounds: {
minx: 'can be negative',
miny: 'can also be negative',
maxx: 'not necessarily the same as metrics.width',
maxy: 'not necessarily the same as metrics.height'
},
capHeight: 'height of the letter H',
ascender: 'distance above the letter x',
xHeight: 'height of the letter x (1ex)',
descender: 'distance below the letter x'
}
}
Array.prototype.slice.call(
document.getElementsByTagName('canvas'), 0
).forEach(function(c, i){
if (i > 0) document.body.removeChild(c);
});
document.getElementById('illustrationContainer').innerHTML = [
'<div style="margin:0; padding:0; position: relative; font-size:',fontSize,'; line-height: 1em; outline:1px solid black;">',
testtext,
'<div class="__ascender" style="position: absolute; width:100%; top:',myMetrics.relative.offset,'em; height:',myMetrics.relative.ascender,'em; background:rgba(220,0,5,.5);"></div>',
'<div class="__xHeight" style="position: absolute; width:100%; top:',myMetrics.relative.offset + myMetrics.relative.ascender,'em; height:',myMetrics.relative.xHeight,'em; background:rgba(149,204,13,.5);"></div>',
'<div class="__xHeight" style="position: absolute; width:100%; top:',myMetrics.relative.offset + myMetrics.relative.ascender + myMetrics.relative.xHeight,'em; height:',myMetrics.relative.descender,'em; background:rgba(13,126,204,.5);"></div>',
'</div>'
].join('');
myMetrics.illustrationMarkup = document.getElementById('illustrationContainer').innerHTML;
var logstring = ["/* metrics for", fontName,
"*/\nvar metrics =",
JSON.stringify(myMetrics, null, ' ')].join(' ');
document.getElementById('log').textContent = logstring;
}
于 2016-02-07T23:06:35.743 回答