Raphael JS Text Along path

问题:

I am looking for an example or some confirmation on a concept. Looking to use Raphael JS on an app and want to be able to warp text similar to how graphic design applications such as Illustrator do.

回答1:

This isn't too difficult using path.getPointAtLength, as Kevin Nielsen suggests:

path = paper.path("M50,100c40,-50 270,50 300,0").attr("stroke", "#CCC");
message = "I want to do this in RaphaelJS";

//since not every letter is the same width, get the placement for each letter 
//along the length of the string
//however, Raphael appears to group the width of letters into intervals of 4px,
//so this won't be perfect        
for (; c < message.length; c += 1) {
        letter = paper.text(0, 0, message[c]).attr({"text-anchor" : "start"});
    letters.push(letter);
    places.push(message_length);
    //spaces get a width of 0, so set min at 4px
    message_length += Math.max(4, letter.getBBox().width);
}

ratio = path.getTotalLength() / message_length;
fontsize = 10 * ratio;

for (c = 0; c < letters.length; c += 1) {
    letters[c].attr("font-size", fontsize + "px"); 
    p = path.getPointAtLength(places[c] * ratio);
    //there does appear to be a bug in p.alpha around 180. Here's the fix
    letters[c].attr({ x: p.x, y: p.y, transform: 'r' + (p.alpha < 180 ? p.alpha + 180 : p.alpha)});
}

jsFiddle

回答2:

Here's an adaptation of Chris Wilson's code, refactored as a drop-in function, with added features:

• IE8 / VML mode support and Gecko/Firefox support (by defining the rotation origin - without this, IE8 and Firefox go nuts throwing the text all around the page)
• A small adjustment to make text less ugly in Gecko browsers (e.g. Firefox) - without this, these increase the letter spacing arbitrarily
• Support for manually defined font sizes and letter spacing, as well as dynamic 'fill the path' sizes and spacing
• Support for manual kerning (fine-tuning letter spacing character by character). Text on a path often creates really ugly letter spaces; this allows you to define manual tweaks to fix these, by:
  • Numeric position in the string, or,
  • Character, or,
  • Character pairs (applying to instances of a character based on the preceding character, e.g. the below example tightens 'ae' pairs and widens 'rn' pairs)

JSBIN DEMO

function textOnPath( message, path, fontSize, letterSpacing, kerning, geckoKerning) {
    // only message and path are required, other args are optional
    // if fontSize or letterSpacing are undefined, they are calculated to fill the path
    // 10% of fontSize is usually good for manual letterspacing

    // Gecko, i.e. Firefox etc, inflates and alters the letter spacing
    var gecko = /rv:([^\)]+)\) Gecko\/\d{8}/.test(navigator.userAgent||'') ? true : false;

    var letters = [], places = [], messageLength = 0;
    for (var c=0; c < message.length; c++) {
        var letter = paper.text(0, 0, message[c]).attr({"text-anchor" : "middle"});
        letters.push(letter);

        if (kerning) {
            if(gecko && geckoKerning) {
                kerning = geckoKerning;
            }
            var character = letter.attr('text'), kern = 0;
            var predecessor = letters[c-1] ? letters[c-1].attr('text') : '';

            if (kerning[c]) {
                kern = kerning[c];
            } else if (kerning[character]) {
                if( typeof kerning[character] === 'object' ) {
                    kern = kerning[character][predecessor] || kerning[character]['default'] || 0;
                } else {
                    kern = kerning[character];
                }
            }
            if(kerning['default'] ) {
                kern = kern + (kerning['default'][predecessor] || 0);
            }            
            messageLength += kern;
        }

        places.push(messageLength);
        //spaces get a width of 0, so set min at 4px
        messageLength += Math.max(4.5, letter.getBBox().width);
    }

    if( letterSpacing ){
        if (gecko) {
            letterSpacing = letterSpacing * 0.83;
        }
    } else {
        letterSpacing = letterSpacing || path.getTotalLength() / messageLength;
    }
    fontSize = fontSize || 10 * letterSpacing;

    for (c = 0; c < letters.length; c++) {
        letters[c].attr("font-size", fontSize + "px");
        p = path.getPointAtLength(places[c] * letterSpacing);
        var rotate = 'R' + (p.alpha < 180 ? p.alpha + 180 : p.alpha > 360 ? p.alpha - 360 : p.alpha )+','+p.x+','+p.y;
    letters[c].attr({ x: p.x, y: p.y, transform: rotate });
    }
}