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HTML 

              
                <body>

  <div id="canvas"></div>

  <div class="plane">
    <!-- notice here we are using the data-sampler attribute to name our sampler uniforms -->
    <img src="https://www.martin-laxenaire.fr/csstricks/images/displacement.jpg" data-sampler="displacement" crossorigin="anonymous" />
    <video src="https://www.martin-laxenaire.fr/csstricks/videos/plane-video-texture.mp4" data-sampler="firstTexture" crossorigin="anonymous"></video>
    <video src="https://www.martin-laxenaire.fr/csstricks/videos/plane-video-texture-2.mp4" data-sampler="secondTexture" crossorigin="anonymous"></video>
  </div>

  <div id="enter-site-wrapper" class="flex-wrapper">
    <span id="enter-site">
      Click to enter site
    </span>
  </div>

  <script id="plane-vs" type="x-shader/x-vertex">
    #ifdef GL_ES
    precision mediump float;
    #endif

    // default mandatory variables
    attribute vec3 aVertexPosition;
    attribute vec2 aTextureCoord;

    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;
    
    // our texture matrices
    // notice how it matches our data-sampler attributes + "Matrix"
    uniform mat4 firstTextureMatrix;
    uniform mat4 secondTextureMatrix;

    // varyings
    varying vec3 vVertexPosition;
    // our displacement texture will use original texture coords attributes
    varying vec2 vTextureCoord;
    // our videos will use texture coords based on their texture matrices
    varying vec2 vFirstTextureCoord;
    varying vec2 vSecondTextureCoord;

    // custom uniforms
    uniform float uTransitionTimer;

    void main() {

      vec3 vertexPosition = aVertexPosition;

      gl_Position = uPMatrix * uMVMatrix * vec4(vertexPosition, 1.0);

      // varyings
      // texture coords attributes because we want our displacement texture to be contained
      vTextureCoord = aTextureCoord;
      // our videos texture coords based on their texture matrices
      vFirstTextureCoord = (firstTextureMatrix * vec4(aTextureCoord, 0.0, 1.0)).xy;
      vSecondTextureCoord = (secondTextureMatrix * vec4(aTextureCoord, 0.0, 1.0)).xy;
      // vertex position as usual
      vVertexPosition = vertexPosition;
    }
  </script>
  <script id="plane-fs" type="x-shader/x-fragment">
    #ifdef GL_ES
    precision mediump float;
    #endif

    // all our varyings
    varying vec3 vVertexPosition;
    varying vec2 vTextureCoord;
    varying vec2 vFirstTextureCoord;
    varying vec2 vSecondTextureCoord;

    // custom uniforms
    uniform float uTransitionTimer;

    // our textures samplers
    // notice how it matches our data-sampler attributes
    uniform sampler2D firstTexture;
    uniform sampler2D secondTexture;
    uniform sampler2D displacement;

    void main( void ) {
      // our texture coords
      vec2 textureCoords = vTextureCoord;

    // our displacement texture
    vec4 displacementTexture = texture2D(displacement, textureCoords);

    // our displacement factor is a float varying from 1 to 0 based on the timer
    float displacementFactor = 1.0 - (cos(uTransitionTimer / (60.0 / 3.141592)) + 1.0) / 2.0;

    // the effect factor will tell which way we want to displace our pixels
    // the farther from the center of the videos, the stronger it will be
    vec2 effectFactor = vec2((textureCoords.x - 0.5) * 0.75, (textureCoords.y - 0.5) * 0.75);

    // calculate our displaced coordinates of the first video
    vec2 firstDisplacementCoords = vec2(vFirstTextureCoord.x - displacementFactor * (displacementTexture.r * effectFactor.x), vFirstTextureCoord.y- displacementFactor * (displacementTexture.r * effectFactor.y));
    // opposite displacement effect on the second video
    vec2 secondDisplacementCoords = vec2(vSecondTextureCoord.x - (1.0 - displacementFactor) * (displacementTexture.r * effectFactor.x), vSecondTextureCoord.y - (1.0 - displacementFactor) * (displacementTexture.r * effectFactor.y));

    // apply the textures
    vec4 firstDistortedColor = texture2D(firstTexture, firstDisplacementCoords);
    vec4 secondDistortedColor = texture2D(secondTexture, secondDisplacementCoords);

    // blend both textures based on our displacement factor
    vec4 finalColor = mix(firstDistortedColor, secondDistortedColor, displacementFactor);

    // handling premultiplied alpha
    finalColor = vec4(finalColor.rgb * finalColor.a, finalColor.a);

    // apply our shader
    gl_FragColor = finalColor;
    }
  </script>


  <script src="https://www.curtainsjs.com/build/curtains.min.js" type="text/javascript"></script>
!

CSS 

              
                @media screen {

    body {
        margin: 0;
        font-size: 18px;
        font-family: 'PT Sans', Verdana, sans-serif;
        background: #212121;
        line-height: 1.4;

        height: 100vh;
        width: 100vw;
        overflow: hidden;
    }

    /*** canvas ***/

    #canvas {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100vh;

        z-index: 10;

        opacity: 0;
        transition: opacity 0.5s ease-in;
    }

    .video-started #canvas {
        opacity: 1;
    }

    .plane {
        position: absolute;
        top: 0;
        right: 0;
        bottom: 0;
        left: 0;
        cursor: pointer;
        z-index: 15;
    }

    .plane img, .plane video {
        display: none;
    }


    #enter-site-wrapper {
        display: flex;
        justify-content: center;
        align-items: center;
        align-content: center;

        position: absolute;
        top: 0;
        right: 0;
        bottom: 0;
        left: 0;
        z-index: 30;

        opacity: 0;
        transition: opacity 0.5s ease-in;
    }

    .curtains-ready #enter-site-wrapper {
        opacity: 1;
    }

    .curtains-ready.video-started #enter-site-wrapper {
        opacity: 0;
        pointer-events: none;
    }

    #enter-site {
        padding: 20px;
        color: white;
        background: #ee6557;
        max-width: 200px;
        text-align: center;
        cursor: pointer;
    }

}


@media screen and (max-width: 1000px) {

    .multi-textures {
        font-size: 2em;
    }

}
!

JS 

              
                window.onload = function() {

    // here we will handle which texture is visible and the timer to transition between images
    var activeTexture = 1;
    var transitionTimer = 0;

    // set up our WebGL context and append the canvas to our wrapper
    var webGLCurtain = new Curtains({
      container: "canvas"
    });

    // get our plane element
    var planeElements = document.getElementsByClassName("plane");

    // some basic parameters
    // we don't need to specifiate vertexShaderID and fragmentShaderID because we already passed it via the data attributes of the plane HTML element
    var params = {
        vertexShaderID: "plane-vs",
        fragmentShaderID: "plane-fs",
        imageCover: false, // our displacement texture has to fit the plane
        uniforms: {
            transitionTimer: {
                name: "uTransitionTimer",
                type: "1f",
                value: 0,
            },
        },
    }
    
    // create our plane
    var plane = webGLCurtain.addPlane(planeElements[0], params);

    // if our plane has been successfully created
    plane && plane.onReady(function() {
        // display the button
        document.body.classList.add("curtains-ready");

        // when our plane is ready we add a click event listener that will switch the active texture value
        planeElements[0].addEventListener("click", function() {
            if(activeTexture == 1) {
                activeTexture = 2;
            }
            else {
                activeTexture = 1;
            }
        });

        // click to play the videos
        document.getElementById("enter-site").addEventListener("click", function() {
            // display canvas and hide the button
            document.body.classList.add("video-started");

            // play our videos
            plane.playVideos();
        }, false);

    }).onRender(function() {
        // increase or decrease our timer based on the active texture value
        // at 60fps this should last one second
        if(activeTexture == 2) {
            transitionTimer = Math.min(60, transitionTimer + 1);
        }
        else {
            transitionTimer = Math.max(0, transitionTimer - 1);
        }
        // update our transition timer uniform
        plane.uniforms.transitionTimer.value = transitionTimer;
    });
}
!
999px

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