strugee strugee - 5 months ago 38
CSS Question

How can I animate the drawing of text on a web page?

I want to have a web page which has one centered word.

I want this word to be drawn with an animation, such that the page "writes" the word out the same way that we would, i.e. it starts at one point and draws lines and curves over time such that the end result is a glyph.

I do not care if this is done with

<canvas>
or the DOM, and I don't care whether it's done with JavaScript or CSS. The absence of jQuery would be nice, but not required.

How can I do this? I've searched exhaustively with no luck.

K3N K3N
Answer

I want this word to be drawn with an animation, such that the page "writes" the word out the same way that we would

Canvas version

This will draw single chars more like one would write by hand. It uses a long dash-pattern where the on/off order is swapped over time per char. It also has a speed parameter.

Snapshot
Example animation (see demo below)

To increase realism and the organic feel, I added random letter-spacing, an y delta offset, transparency, a very subtle rotation and finally using an already "handwritten" font. These can be wrapped up as dynamic parameters to provide a broad range of "writing styles".

For a even more realistic look the path data would be required which it isn't by default. But this is a short and efficient piece of code which approximates hand-written behavior, and easy to implement.

How it works

By defining a dash pattern we can create marching ants, dotted lines and so forth. Taking advantage of this by defining a very long dot for the "off" dot and gradually increase the "on" dot, it will give the illusion of drawing the line on when stroked while animating the dot length.

Since the off dot is so long the repeating pattern won't be visible (the length will vary with the size and characteristics of the typeface being used). The path of the letter will have a length so we need to make sure we are having each dot at least covering this length.

For letters that consists of more than one path (f.ex. O, R, P etc.) as one is for the outline, one is for the hollow part, the lines will appear to be drawn simultaneously. We can't do much about that with this technique as it would require access to each path segment to be stroked separately.

Compatibility

For browsers that don't support the canvas element an alternative way to show the text can be placed between the tags, for example a styled text:

<canvas ...>
    <div class="txtStyle">STROKE-ON CANVAS</div>
</canvas>

Demo

This produces the live animated stroke-on (no dependencies) -

var ctx = document.querySelector("canvas").getContext("2d"),
    dashLen = 220, dashOffset = dashLen, speed = 5,
    txt = "STROKE-ON CANVAS", x = 30, i = 0;

ctx.font = "50px Comic Sans MS, cursive, TSCu_Comic, sans-serif"; 
ctx.lineWidth = 5; ctx.lineJoin = "round"; ctx.globalAlpha = 2/3;
ctx.strokeStyle = ctx.fillStyle = "#1f2f90";

(function loop() {
  ctx.clearRect(x, 0, 60, 150);
  ctx.setLineDash([dashLen - dashOffset, dashOffset - speed]); // create a long dash mask
  dashOffset -= speed;                                         // reduce dash length
  ctx.strokeText(txt[i], x, 90);                               // stroke letter

  if (dashOffset > 0) requestAnimationFrame(loop);             // animate
  else {
    ctx.fillText(txt[i], x, 90);                               // fill final letter
    dashOffset = dashLen;                                      // prep next char
    x += ctx.measureText(txt[i++]).width + ctx.lineWidth * Math.random();
    ctx.setTransform(1, 0, 0, 1, 0, 3 * Math.random());        // random y-delta
    ctx.rotate(Math.random() * 0.005);                         // random rotation
    if (i < txt.length) requestAnimationFrame(loop);
  }
})();
canvas {background:url(http://i.imgur.com/5RIXWIE.png)}
<canvas width=630></canvas>

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