问题
The question says it all pretty much. I've been searching around and starting to worry that it's impossible.
I've got this canvas element that I'm drawing text to. I want to set the letter spacing similar to the CSS letter-spacing attribute. By that I mean increasing the amount of pixels between letters when a string is drawn.
My code for drawing the text is like so, ctx is the canvas context variable.
ctx.font = "3em sheepsans";
ctx.textBaseline = "middle";
ctx.textAlign = "center";
ctx.fillStyle = "rgb(255, 255, 255)";
ctx.fillText("Blah blah text", 1024 / 2, 768 / 2);
I've tried adding ctx.letterSpacing = "2px"; before the drawing but with no avail. Is there a way to do this just with a simple setting, or will I have to make a function to individually draw each character with the spacing in mind?
回答1:
I'm not sure if it should work (per specs), but in some browsers (Chrome) you can set the letter-spacing CSS property on the <canvas> element itself, and it will be applied to all text drawn on the context. (Works in Chrome v56, does not work in Firefox v51 or IE v11.)
Note that in Chrome v56 you must re-get the canvas 2d context (and re-set any values you care about) after each change to the letter-spacing style; the spacing appears to be baked into the 2d context that you get.
Example: https://jsfiddle.net/hg4pbsne/1/
var inp = document.querySelectorAll('input'),
can = document.querySelector('canvas'),
ctx = can.getContext('2d');
can.width = can.offsetWidth;
[].forEach.call(inp,function(inp){ inp.addEventListener('input', redraw, false) });
redraw();
function redraw(){
ctx.clearRect(0,0,can.width,can.height);
can.style.letterSpacing = inp[0].value + 'px';
ctx = can.getContext('2d');
ctx.textAlign = 'center';
ctx.textBaseline = 'middle';
ctx.font = '4em sans-serif';
ctx.fillText('Hello', can.width/2, can.height*1/4);
can.style.letterSpacing = inp[1].value + 'px';
ctx = can.getContext('2d');
ctx.textAlign = 'center';
ctx.textBaseline = 'middle';
ctx.font = '4em sans-serif';
ctx.fillText('World', can.width/2, can.height*3/4);
};canvas { background:white }
canvas, label { display:block; width:400px; margin:0.5em auto }<canvas></canvas>
<label>hello spacing: <input type="range" min="-20" max="40" value="1" step="0.1"></label>
<label>world spacing: <input type="range" min="-20" max="40" value="1" step="0.1"></label>Original, cross-browser answer:
This is not possible; the HTML5 Canvas does not have all the text-transformation power of CSS in HTML. I would suggest that you should combine the appropriate technologies for each usage. Use HTML layered with Canvas and perhaps even SVG, each doing what it does best.
Note also that 'rolling your own'—drawing each character with a custom offset—is going to produce bad results for most fonts, given that there are letter kerning pairs and pixel-aligned font hinting.
回答2:
You can't set the letter spacing property, but you you can accomplish wider letter spacing in canvas by inserting one of the various white spaces in between every letter in the string. For instance
ctx.font = "3em sheepsans";
ctx.textBaseline = "middle";
ctx.textAlign = "center";
ctx.fillStyle = "rgb(255, 255, 255)";
var ctext = "Blah blah text".split("").join(String.fromCharCode(8202))
ctx.fillText(ctext, 1024 / 2, 768 / 2);
This will insert a hair space between every letter.
Using 8201 (instead of 8202) will insert the slightly wider thin space
For more white space options, see this list of Unicode Spaces
This method will help you to preserve the font's kerning much more easily than manually positioning each letter, however you wont be able to tighten your letter spacing this way.
回答3:
You can't set letter-spacing as a property of the Canvas context. You can only achieve the effect by doing manual spacing, sorry. (As in, drawing each letter manually increasing the x by some pixel amount on each)
For the record, you can set a few text properties by using ctx.font but letter-spacing is not one of them. The ones you can set are: "font-style font-variant font-weight font-size/line-height font-family"
For instance you can technically write ctx.font = "bold normal normal 12px/normal Verdana" (or any omission of any of those) and it will parse correctly.
回答4:
here's some coffeescript that allows you to set kerning to your context like so
tctx = tcanv.getContext('2d')
tctx.kerning = 10
tctx.fillStyle = 'black'
tctx.fillText 'Hello World!', 10, 10
the supporting code is:
_fillText = CanvasRenderingContext2D::fillText
CanvasRenderingContext2D::fillText = (str, x, y, args...) ->
# no kerning? default behavior
return _fillText.apply this, arguments unless @kerning?
# we need to remember some stuff as we loop
offset = 0
_.each str, (letter) =>
_fillText.apply this, [
letter
x + offset + @kerning
y
].concat args # in case any additional args get sent to fillText at any time
offset += @measureText(letter).width + @kerning
The javascript would be
var _fillText,
__slice = [].slice;
_fillText = CanvasRenderingContext2D.prototype.fillText;
CanvasRenderingContext2D.prototype.fillText = function() {
var args, offset, str, x, y,
_this = this;
str = arguments[0], x = arguments[1], y = arguments[2], args = 4 <= arguments.length ? __slice.call(arguments, 3) : [];
if (this.kerning == null) {
return _fillText.apply(this, arguments);
}
offset = 0;
return _.each(str, function(letter) {
_fillText.apply(_this, [letter, x + offset + _this.kerning, y].concat(args));
offset += _this.measureText(letter).width + _this.kerning;
});
};
回答5:
To allow for 'letter kerning pairs' and the like, I've written the following. It should take that into account, and rough testing suggests it does. If you have any comments on it then I would point you to my question on the subject (Adding Letter Spacing in HTML Canvas)
Basically it uses measureText() to get the width of the whole string, and then removes the first character of the string and measures the width of the remaining string, and uses the difference to calculate the correct positioning - thus taking into account kerning pairs and the like. See the given link for more pseudocode.
Here's the HTML:
<canvas id="Test1" width="800px" height="200px"><p>Your browser does not support canvas.</p></canvas>
Here's the code:
this.fillTextWithSpacing = function(context, text, x, y, spacing)
{
//Start at position (X, Y).
//Measure wAll, the width of the entire string using measureText()
wAll = context.measureText(text).width;
do
{
//Remove the first character from the string
char = text.substr(0, 1);
text = text.substr(1);
//Print the first character at position (X, Y) using fillText()
context.fillText(char, x, y);
//Measure wShorter, the width of the resulting shorter string using measureText().
if (text == "")
wShorter = 0;
else
wShorter = context.measureText(text).width;
//Subtract the width of the shorter string from the width of the entire string, giving the kerned width of the character, wChar = wAll - wShorter
wChar = wAll - wShorter;
//Increment X by wChar + spacing
x += wChar + spacing;
//wAll = wShorter
wAll = wShorter;
//Repeat from step 3
} while (text != "");
}
Code for demo/eyeball test:
element1 = document.getElementById("Test1");
textContext1 = element1.getContext('2d');
textContext1.font = "72px Verdana, sans-serif";
textContext1.textAlign = "left";
textContext1.textBaseline = "top";
textContext1.fillStyle = "#000000";
text = "Welcome to go WAVE";
this.fillTextWithSpacing(textContext1, text, 0, 0, 0);
textContext1.fillText(text, 0, 100);
Ideally I'd throw multiple random strings at it and do a pixel by pixel comparison. I'm also not sure how good Verdana's default kerning is, though I understand it's better than Arial - suggestions on other fonts to try gratefully accepted.
So... so far it looks good. In fact it looks perfect. Still hoping that someone will point out any flaws in the process.
In the meantime I will put this here for others to see if they are looking for a solution on this.
回答6:
Not true. You can add letter-spacing property to the canvas element in css and it works perfectly. No need for complicated workarounds. I just figured it out right now in my canvas project. i.e.: canvas { width: 480px; height: 350px; margin: 30px auto 0; padding: 15px 0 0 0; background: pink; display: block; border: 2px dashed brown; letter-spacing: 0.1em; }
回答7:
Actually letter spacing concept canvas is not supporting.
So i used javascript to do this.
var value = $('#sourceText1').val().split("").join(" ");
OR
var sample_text = "Praveen Chelumalla";
var text = sample_text.split("").join(" ");
回答8:
I don't know about other people but I have adjusted line spacing by increasing the y value on the text that I am writing. I'm actually splitting a string by spaces and kicking each word down a line inside a loop. The numbers i use are based on the default font. If you use a different font that these numbers may need to be adjusted.
// object holding x and y coordinates
var vectors = {'x':{1:100, 2:200}, 'y':{1:0, 2:100}
// replace the first letter of a word
var newtext = YOURSTRING.replace(/^\b[a-z]/g, function(oldtext) {
// return it uppercase
return oldtext.toUpperCase();
});
// split string by spaces
newtext = newtext.split(/\s+/);
// line height
var spacing = 10 ;
// initial adjustment to position
var spaceToAdd = 5;
// for each word in the string draw it based on the coordinates + spacing
for (var c = 0; c < newtext.length; c++) {
ctx.fillText(newtext[c], vectors.x[i], vectors.y[i] - spaceToAdd);
// increment the spacing
spaceToAdd += spacing;
}
回答9:
Letter spacing in canvas IS SUPPORTED, I used this
canvas = document.getElementById('canvas');
canvas.style.letterSpacing = '2px';
回答10:
I use:
ctx.font = "32px Tahoma";//set font
ctx.scale(0.75,1);//important! the scale
ctx.fillText("LaFeteParFete test text", 2, 274);//draw
ctx.setTransform(1,0,0,1,0,0);//reset transform
来源：https://stackoverflow.com/questions/8952909/letter-spacing-in-canvas-element