SVG waves with feDisplacementMap by Gabi on CodePen

First thing first: my English may not be as good as required for writing a post on Codepen. Please feel free to correct my spelling and my grammar in the comments below.

About <feDisplacementMap>

The filter primitive uses the pixel values of the image from in2 to spatially displace the image from in.

  <feDisplacementMap in2="img1" in="img2" scale="15" xChannelSelector="R" yChannelSelector="G"/>

The scale attribute defines the displacement scale.

The xChannelSelector attribute indicates which channel from in2 is used to displace the pixels from in along the x-axis. Possible values for the xChannelSelector attribute are:

R (the red channel)
G (the green channel)
B (the blue channel) or
A (the alpha channel)

The same goes for the yChannelSelector attribute, only this time the pixels are displaced along the y-axis.

A static example

In the following example I have two SVG elements: A first one, a witness where I'm displaying the radial gradient used as a value for in2, and a second one for the filtered image.

A few definitions:

In the <defs> element I'm creating a radial gradient like this:

     <radialGradient id="rg" r=".9">  
      <stop offset="0%" stop-color="#f00"></stop>
      <stop offset="10%" stop-color="#000"></stop>
      <stop offset="20%" stop-color="#f00"></stop>
      <stop offset="30%" stop-color="#000"></stop>
      <stop offset="40%" stop-color="#f00"></stop>
      <stop offset="50%" stop-color="#000"></stop>
      <stop offset="60%" stop-color="#f00"></stop>
      <stop offset="70%" stop-color="#000"></stop>
      <stop offset="80%" stop-color="#f00"></stop>
      <stop offset="90%" stop-color="#000"></stop> 
      <stop offset="100%" stop-color="#f00"></stop>
    </radialGradient>

In addition I'm creating a <rect> element filled with the gradient above.

  <rect id="witness" width="300" height="300" fill="url(#rg)"></rect>

Also in the <defs> I'm creating the filter.

Building the filter

For the filter I'm using primitiveUnits="objectBoundingBox". This means that any length values within the filter definitions represent fractions or percentages of the bounding box.

In the case of filters defaults for x and y are -10% and defaults for width and height are 120%. The default for filterUnits is "objectBoundingBox". I'm OK with these.

  <filter id="f" primitiveUnits="objectBoundingBox">
. . . .
</filter>

I'm using the feImage filter to reference and use the rect id="witness" defined above (a fragment in the same document). Unfortunately Firefox do not support fragments. I'll fix this latter.

  <filter id="f" primitiveUnits="objectBoundingBox" >
      <feImage result="pict2" xlink:href="#witness"></feImage>
      . . . . 
</filter>

The <feDisplacementMap> filter primitive will use the red channel (R) from this image (result="pict2") to displace the pixels from the source graphic (the dog image in this case).

  <filter id="f" primitiveUnits="objectBoundingBox" >
      <feImage result="pict2" xlink:href="#gradient"></feImage>
      <feDisplacementMap scale=".05" xChannelSelector="R" yChannelSelector="R" in2="pict2" in="SourceGraphic">
   </feDisplacementMap>
</filter>

Now I can apply this filter (#f) to the image:

  <image filter="url(#f)" xlink:href=". . . beagle400.jpg" width="300" height="300" id="Darwin" ></image>

And this is the result (for now it works only in Chrome and in Edge):

Animating the wave

In the second example I'm taking this a step further: I'm animating the radial gradient in a ripple movement.

Practically I'm animating the value of the offset of each stop element. First I need the array of the stop elements:

  let radGrd = Array.from(document.querySelectorAll("#rg stop"));

Now I can use the method map to update the value of the offset for each stop element.

  let displacement = 0;
let speed = 0.2;

function AnimateOffset() {
  radGrd.map((gr,i) =>{
    gr.setAttributeNS(null, "offset", (i - 2) * 10 + displacement + "%");
  });

  if (displacement <= 20) {
    displacement += speed;
  } else {
    displacement = 0;
  }
  window.requestAnimationFrame(AnimateOffset);
}
window.requestAnimationFrame(AnimateOffset);

And it works!!

Unfortunately it works only in Chrome and in Edge. The culprit is <feImage> and the bug 455986.

However there is a way to ~~fix~~ elude this problem. The solution is to use SVG as data:URI instead of fragments.

You can read in detail about this here in Codepen: Optimizing SVGs in data URI, a post by Taylor Hunt.

How to transform an SVG to data:URI

One way to do it is using the unencoded SVG code like this:

'data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" width="300px" height="300px" viewBox="0 0 300 300"><path fill="#FFFFFF" stroke="#ED1D24" d=" . . . . /><svg>'

See an example here.

And this works but, again, not in all browsers. It can be done better. There are a few rules to follow:

#1. Prepare the SVG as if it were an external SVG file (declaring namespaces):

  <svg version='1.1' xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='300 ' height='300'>
<defs>
   <radialGradient id="rg" r=".9">  
      <stop offset="0%" stop-color="#f00"></stop>
      <stop offset="10%" stop-color="#000"></stop>
      <stop offset="20%" stop-color="#f00"></stop>
      <stop offset="30%" stop-color="#000"></stop>
      <stop offset="40%" stop-color="#f00"></stop>
      <stop offset="50%" stop-color="#000"></stop>
      <stop offset="60%" stop-color="#f00"></stop>
      <stop offset="70%" stop-color="#000"></stop>
      <stop offset="80%" stop-color="#f00"></stop>
      <stop offset="90%" stop-color="#000"></stop> 
      <stop offset="100%" stop-color="#f00"></stop>
   </radialGradient> 
 </defs>  
   <rect id="witness" width="300" height="300" fill="url(#rg)"></rect>
</svg>

#2. Put all the attributes inside between single-quotes and remove the spaces and line breaks between tags:

  <svg version='1.1' xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='300 ' height='300'><defs><radialGradient id='rg' r=".9"><stop offset='0%' stop-color='#f00'></stop><stop offset='10% 'stop-color='#000'></stop><stop offset='20%' stop-color='#f00'></stop><stop offset='30%' stop-color='#000'></stop><stop offset='40%' stop-color='#f00'></stop><stop offset='50%' stop-color='#000'></stop><stop offset='60%' stop-color='#f00'></stop><stop offset='70%' stop-color='#000'></stop><stop offset='80% 'stop-color='#f00'></stop><stop offset='90%' stop-color='#f00'></stop><stop offset='100%' stop-color='#f00'></stop><radialGradient></defs><rect id='gradient' x='0' y='0' width='300' height='300' fill='url(#rg)' /></svg>

#3. Code all the unsafe characters but not the white space:

< becomes %3C
> becomes %3E

For example <svg> becomes %3Csvg%3E

# becomes %23

For examples #abcfef becomes %23abcdef

The hyphen - becomes %2D

For example stroke-width='2' becomes stroke%2Dwidth='2'

% becomes %25

For example width ='50%' becomes width ='50%25'

You may see an example here: How to transform an SVG to data:URI

Now <feImage> should look like this:

  <feImage result="pict2" xlink:href="data:image/svg+xml;utf8,%3Csvg version='1.1' xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='300' height='300'%3E%3Cdefs%3E%3CradialGradient id='rg' r='.9'%3E%3Cstop offset='0%' stop%2Dcolor='%23f00'%3E%3C/stop%3E%3Cstop offset='10%' stop%2Dcolor='%23000'%3E%3C/stop%3E%3Cstop offset='20%' stop%2Dcolor='%23f00'%3E%3C/stop%3E%3Cstop offset='30%' stop%2Dcolor='%23000'%3E%3C/stop%3E%3Cstop offset='40%' stop%2Dcolor='%23f00'%3E%3C/stop%3E%3Cstop offset='50%' stop%2Dcolor='%23000'%3E%3C/stop%3E%3Cstop offset='60%' stop%2Dcolor='%23f00'%3E%3C/stop%3E%3Cstop offset='70%' stop%2Dcolor='%23000'%3E%3C/stop%3E%3Cstop offset='80%' stop%2Dcolor='%23f00'%3E%3C/stop%3E%3Cstop offset='90%' stop%2Dcolor='%23000'%3E%3C/stop%3E%3Cstop offset='100%' stop%2Dcolor='%23f00'%3E%3C/stop%3E%3C/radialGradient%3E%3C/defs%3E%3Crect id='gradient' x='0' y='0' width='300' height='300' fill='url(%23rg)'%3E%3C/rect%3E%3C/svg%3E">
</feImage>

In order to animate the whole thing I'm writing a function that builds the string for the data:URI. In the comments I'm showing the SVG markup equivalent.

  function setXlinkHref(){
  /*
  <svg width="300" height="300">
   <defs>
     <radialGradient id="rg" r=".9"> 
  */
  let xlinkHref = "data:image/svg+xml;utf8,%3Csvg version='1.1' xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='300' height='300'%3E%3Cdefs%3E%3CradialGradient id='rg' r='.9'%3E"; 
  /*
       <stop offset='0%' stop-color='#f00'></stop>
       <stop offset='10% 'stop-color='#000'></stop>
       <stop offset='20%' stop-color='#f00'></stop>
       <stop offset='30%' stop-color='#000'></stop>
       <stop offset='40%' stop-color='#f00'></stop>
       <stop offset='50%' stop-color='#000'></stop>
       <stop offset='60%' stop-color='#f00'></stop>
       <stop offset='70%' stop-color='#000'></stop>
       <stop offset='80% 'stop-color='#f00'></stop>
       <stop offset='90%' stop-color='#f00'></stop> 
       <stop offset='100%' stop-color='#f00'></stop>
  */  
for(var i = 0; i < 11; i++){
  xlinkHref += `%3Cstop 
                offset='${((i-2)*10)+displacement}%25' 
                stop%2Dcolor='%23${(i%2 == 0)? 'f00' : '000'}'%3E%3C/stop%3E`;
}  
   /*
   </radialGradient> 
   <rect id="gradient" x="0" y="0" width="300" height="300" fill="url(#rg)"></rect>
  </svg>
   */  
xlinkHref += "%3C/radialGradient%3E%3C/defs%3E%3Crect id='gradient' x='0' y='0' width='300' height='300' fill='url(%23rg)'%3E%3C/rect%3E%3C/svg%3E";

return xlinkHref;
}

I'll be using the returned value of this function to animate the value for the <feimage>'s attribute xlink:href.

  filterFeImage.setAttributeNS(xlink, "href", xlinkHref);

How to fill an SVG path with an image

I need to add something more in the <defs>: a pattern. This is because I want to delete the <radialGradient> element and I need a way to paint an image on the <rect id="witness">.

  <defs>
. . . . . . . . 
<pattern id="imageFill" width="1" height="1"
viewBox="0 0 300 300" >
<image id="ripples" width="300" height="300"
xlink:href="" />
</pattern>
</defs> 

<rect id="witness" width="300" height="300" fill="url(#imageFill)" ></rect>

This is a technique I've learned from Amelia's new book.

The animation

The animation uses the returned value of setXlinkHref() to update the xlink:href attribute for the <feImage> and for the ripples image within the pattern.

    let xlinkHref = setXlinkHref();
  filterFeImage.setAttributeNS(xlink, "href", xlinkHref);
  ripples.setAttributeNS(xlink, "href", xlinkHref);

Also updates the displacement value (used to displace the ripples).

  function AnimateOffset() {

  let xlinkHref = setXlinkHref();
  filterFeImage.setAttributeNS(xlink, "href", xlinkHref);
  ripples.setAttributeNS(xlink, "href", xlinkHref);

  if (displacement <= 20) {
    displacement += speed;
  } else {
    displacement = 0;
  }

  window.requestAnimationFrame(AnimateOffset);
}

window.requestAnimationFrame(AnimateOffset);

And this is the final result:

This should work in Chrome, Opera, Firefox & Edge.

Thank you for reading. I hope you find it useful.

Rachel Smith Pro @rachsmith on October 20, 2017

Hi Gabi, if you want to, could you make the final Pen public rather than private? Then I can add it to the Pen picks :)

1 Love
Gabi Pro @enxaneta on October 20, 2017

@rachsmith Sorry about that. It's public now.

Love
James Byng @byngj123 on October 26, 2017

You have no idea how long I have looked for something like this! Awesome!!

1 Love
O_Vigilante @o_vigilante on November 8, 2017

Hello,

I only wondering why a simple code doesn't work on Safari. It's because of "feimage" tag? Is there way to make this exemple to support Safari, as well?

Thanks! :)

Love
Gabi Pro @enxaneta on November 8, 2017

@o_vigilante LOL! The filter is sort of working in Safari since the image appears distorted. And it's there. The problem in Safari is that SVG filters are expensive in terms of performance and blocks the animation. Hopefully this will change with the time.

Love
smallma @smallma009 on April 9, 2018

Hello,

I open on Chrome 65 and not work now. Can you help to clarify? Thanks.

Love
Gabi Pro @enxaneta on April 9, 2018

Thank you for commenting @smallma009 . I'm sorry it doesn't work in your computer. I've opened it in Chrome 65 (both Mac & PC) and it works.

Love