Обесцвечивание картинки под курсором

<div id="page-wrap">

      <!-- will hold our WebGL context -->
            <div id="canvas"></div>

            <div id="fullwidth-image">
                <img data-sampler="displacedImage" src="https://www.martin-laxenaire.fr/libs/curtainsjs/examples/ajax-navigation/images/plane-texture-1.jpg" />
            </div>


        <!-- shaders and lib -->

        <script id="mouse-displacement-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;

              // custom variables
              varying vec3 vVertexPosition;
              varying vec2 vTextureCoord;

              varying vec2 vDistortionEffect;

              // custom uniforms
              uniform vec2 uMousePosition;

              void main() {
                vec3 vertexPosition = aVertexPosition;

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

                // varyings
                vTextureCoord = aTextureCoord;
                vVertexPosition = vertexPosition;

                vDistortionEffect = uMousePosition - vec2(vertexPosition.x, vertexPosition.y);
              }
        </script>
        <script id="mouse-displacement-fs" type="x-shader/x-fragment">
              #ifdef GL_ES
                  precision mediump float;
              #endif

             varying vec2 vTextureCoord;
              varying vec2 vDistortionEffect;

              // custom uniforms
              uniform float uDisplacementStrength;

              // our textures samplers
              uniform sampler2D displacedImage;
              uniform sampler2D canvasTexture;

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

                // get our canvas texture
                   vec4 mouseEffect = texture2D(canvasTexture, textureCoords);

                // apply displacement to the texture coords based on our canvas texture RGB
                textureCoords  = textureCoords + mouseEffect .r * vDistortionEffect * (uDisplacementStrength / 10.0);

                // get our image texture
                 vec4 finalColor = texture2D(displacedImage, textureCoords);

                 // get a B&W version of our image texture
                vec4 finalBW = vec4(1.0);
                finalBW.rgb = vec3(finalColor.r * 0.3 + finalColor.g * 0.59 + finalColor.b * 0.11);

                // mix both texture based on our canvas texture
                finalColor = mix(finalColor, finalBW, mouseEffect.r);

                // that's all folks!
                  gl_FragColor = finalColor;
              }
        </script>

@media screen {

    html, body {
        min-height: 100%;
    }

    body {
        margin: 0;
        font-size: 18px;
        font-family: Verdana, sans-serif;
        background: #ffffff;
        line-height: 1.4;
    }

    #page-wrap {
        width: 100%;
        min-height: 100vh;
        position: relative;
        overflow: hidden;
    }

    /*** canvas ***/

    #canvas {
        position: absolute;
        top: 0;
        right: 0;
        height: 100vh;
        left: 0;
    }


    #fullwidth-image {
        position: absolute;
        top: 0;
        left: 0;
        height: 100vh;
        width: 100vw;
    }

    #fullwidth-image img, #fullwidth-image canvas {
        display: none;
    }

    /* handling WebGL context errors */

    .no-webgl #fullwidth-image {
        display: flex;
        justify-content: center;
        align-items: center;
    }

    .no-webgl #fullwidth-image img {
        display: block;
        object-fit: cover;
        min-width: 100%;
        min-height: 100%;
    }
}

var params = {
  webGLCanvasID: "canvas",
  planeElementID: "fullwidth-image",
  
  // TWEAK THOSE VALUES TO CHANGE OVERALL EFFECT
  
  // size of the effect (0: no effect, 1: full window)
  pointerSize: 0.25,
  // how much to increase/decrease opacity on each frame
  opacitySpeed: 0.0125,
  // strength of the velocity of the mouse effect
  velocityStrength: 0.25,
  // the bigger the more displacement
  displacementStrength: 0.25,
  // does not change anything visually, but the smaller the scale the better the performance
  canvasScale: 0.125, 
};

// look at window.onload on line 315

// Constructor function
function MouseEffect(params) {
    // Init the effect
    this.init(params);

    return this;
}

/*
 * Init everything
 */
MouseEffect.prototype.init = function(params) {

    this.curtains = new Curtains(params.webGLCanvasID);

    this.plane = null;

    // get our plane element
    this.planeElement = document.getElementById(params.planeElementID);

    this.pixelRatio = this.curtains.pixelRatio || 1;

    // mouse positions history
    this.mouse = {
        position: {
            x: 0,
            y: 0,
        },
        attributes: [],
    };

    // params
    this.params = {
        pointerSize: params.pointerSize || 0.25,
        opacitySpeed: params.opacitySpeed || 0.0125,

        velocityStrength: params.velocityStrength || 0.25,
        displacementStrength: params.displacementStrength || 0.25,

        canvasScale: params.canvasScale || 0.125,
    };

    this.canvas = null;
    this.canvasContext = null;

    if(
        !document.getElementById(params.webGLCanvasID) ||
        !document.getElementById(params.planeElementID)
    ) {
        console.warn("You must specify a valid ID for the WebGL canvas and the plane element");
        return false;
    }

}

/*
 * Resize the mouse canvas
 */
MouseEffect.prototype.resize = function() {

    if(this.canvas && this.canvasContext) {
        this.canvas.width = this.planeElement.clientWidth * this.pixelRatio * this.params.canvasScale;
        this.canvas.height = this.planeElement.clientHeight * this.pixelRatio * this.params.canvasScale;

        this.canvasContext.width = this.planeElement.clientWidth * this.pixelRatio * this.params.canvasScale;
        this.canvasContext.height = this.planeElement.clientHeight * this.pixelRatio * this.params.canvasScale;

        this.canvasContext.scale(this.pixelRatio * 1 / this.params.canvasScale, this.pixelRatio * 1 / this.params.canvasScale);
        //this.mouse.canvasContext.imageSmoothingEnabled = true;
    }

}


/*
 * Handle mouse/touch moves and push the positions into an array
 */
MouseEffect.prototype.handleMovement = function(e) {

    this.mouse.position.x = e.clientX;
    this.mouse.position.y = e.clientY;

    // touch event
    if(e.targetTouches) {

        this.mouse.position.x = e.targetTouches[0].clientX;
        this.mouse.position.y = e.targetTouches[0].clientY;
    }

    // always check that the plane is still here
    if(this.planeElement && this.plane) {
        var mouseAttributes = {
            x: this.mouse.position.x * Math.pow(this.params.canvasScale, 2),
            y: this.mouse.position.y * Math.pow(this.params.canvasScale, 2),

            scale: 0.05,
            opacity: 1,
            velocity: {
                x: 0,
                y: 0,
            },
        }

        // keep tracks of the initial position of the mouse to calculate velocity
        mouseAttributes.initialPosition = {
            x: mouseAttributes.x,
            y: mouseAttributes.y
        }

        // handle velocity based on past values
        if(this.mouse.attributes.length > 0) {
            mouseAttributes.velocity = {
                x: Math.max(-this.params.canvasScale * 1.25, Math.min(this.params.canvasScale * 1.25, mouseAttributes.initialPosition.x - this.mouse.attributes[this.mouse.attributes.length - 1].initialPosition.x)),
                y: Math.max(-this.params.canvasScale * 1.25, Math.min(this.params.canvasScale * 1.25, mouseAttributes.initialPosition.y - this.mouse.attributes[this.mouse.attributes.length - 1].initialPosition.y)),
            };
        }
      
        // if this is our first mouse move, start drawing again
        if(this.mouse.attributes.length == 0) {
            this.curtains.enableDrawing();
        }

        // push our coords to our mouse coords array
        this.mouse.attributes.push(mouseAttributes);

        // convert our mouse/touch position to coordinates relative to the vertices of the plane
        var mouseCoords = this.plane.mouseToPlaneCoords(this.mouse.position.x, this.mouse.position.y);
        // update our mouse position uniform
        this.plane.uniforms.mousePosition.value = [mouseCoords.x, mouseCoords.y];
    }

}


/*
 * This draws a gradient circle based on mouse attributes positions
 */
MouseEffect.prototype.drawGradientCircle = function(pointerSize, circleAttributes) {
    this.canvasContext.beginPath();

    var gradient = this.canvasContext.createRadialGradient(
        circleAttributes.x, circleAttributes.y, 0,
        circleAttributes.x, circleAttributes.y, pointerSize * circleAttributes.scale * this.params.canvasScale
    );

    // our gradient could go from opaque white to transparent white or from opaque white to transparent black
    // it changes the effect a bit
    gradient.addColorStop(0, 'rgba(255, 255, 255, ' + circleAttributes.opacity + ')');

    // use another gradient stop if we want to add more transparency
    //gradient.addColorStop(0.85, 'rgba(255, 255, 255, 0.05)');

    gradient.addColorStop(1, 'rgba(255, 255, 255, 0)');

    this.canvasContext.fillStyle = gradient;

    this.canvasContext.arc(
        circleAttributes.x, circleAttributes.y, pointerSize * circleAttributes.scale * this.params.canvasScale,
        0, 2 * Math.PI, false
    );
    this.canvasContext.fill();
    this.canvasContext.closePath();
}


/*
 * Drawing onto our canvas
 */
MouseEffect.prototype.animateCanvas = function() {
    // here we will handle our canvas texture animation
    var pointerSize = window.innerWidth > window.innerHeight ?
        Math.floor(this.canvas.height * this.params.pointerSize) :
        Math.floor(this.canvas.width * this.params.pointerSize);

    // clear scene
    this.canvasContext.clearRect(0, 0, this.canvas.width, this.canvas.height);

    // draw a background black rectangle
    this.canvasContext.beginPath();
    this.canvasContext.fillStyle = "black";

    this.canvasContext.rect(0, 0, this.canvas.width, this.canvas.height);
    this.canvasContext.fill();
    this.canvasContext.closePath();

    // draw all our mouse coords
    for(var i = 0; i < this.mouse.attributes.length; i++) {
        this.drawGradientCircle(pointerSize, this.mouse.attributes[i]);
    }
}


/*
 * Once the plane is ready we set the event listeners and handle the render loop
 */
MouseEffect.prototype.handlePlane = function() {

    var self = this;

    self.plane.onReady(function() {

        // on resize, update the resolution uniform
        window.addEventListener("resize", self.resize.bind(self), false);

        document.body.addEventListener("mousemove", self.handleMovement.bind(self), false);
        document.body.addEventListener("touchmove", self.handleMovement.bind(self), {
            passive: true
        });
      
        // for performance purpose, disable the drawing for now
        self.curtains.disableDrawing();
        // render the first frame only to display the picture
        self.curtains.needRender();

    }).onRender(function() {

        for(var i = 0; i < self.mouse.attributes.length; i++) {
            // decrease opacity
            self.mouse.attributes[i].opacity -= self.params.opacitySpeed;

            // apply velocity
            self.mouse.attributes[i].x += self.mouse.attributes[i].velocity.x * self.params.velocityStrength;
            self.mouse.attributes[i].y += self.mouse.attributes[i].velocity.y * self.params.velocityStrength;

            // change scale
            if(self.mouse.attributes[i].opacity >= 0.5) {
                self.mouse.attributes[i].scale += (self.params.opacitySpeed * 2);
            }
            else {
                self.mouse.attributes[i].scale -= self.params.opacitySpeed;
            }

            if(self.mouse.attributes[i].opacity <= 0) {
                // if element is fully transparent, remove it
                self.mouse.attributes.splice(i, 1);
              
                // if this was our last mouse move, disable drawing again
                if(self.mouse.attributes.length == 0) {
                    self.curtains.disableDrawing();
                }
            }
        }

        // draw our mouse coords arrays
        self.animateCanvas();
    });

}

/*
 * If you want to remove the plane cleanly (like if you're navigating away of this page)
 */
MouseEffect.prototype.removePlane = function() {
    var self = this;

    // remove all events
    window.removeEventListener("resize", self.resize);
    document.body.removeEventListener("mousemove", self.handleMovement);
    document.body.removeEventListener("touchmove", self.handleMovement);

    // remove the plane
    self.curtains.removePlane(self.plane);

    self.plane = null;
  
    self.canvas = null;
    self.canvasContext = null;
}


/*
 * Adds the plane and starts the effect
 */
MouseEffect.prototype.addPlane = function() {

    // parameters to apply to our WebGL plane
    this.planeParams = {
        vertexShaderID: "mouse-displacement-vs",
        fragmentShaderID: "mouse-displacement-fs",
        imageCover: true,
        uniforms: {
            mousePosition: {
                name: "uMousePosition",
                type: "2f",
                value: [this.mouse.position.x, this.mouse.position.y],
            },
            mouseEffect: {
                name: "uDisplacementStrength",
                type: "1f",
                value: this.params.displacementStrength,
            },
        },
    };

    // create our plane
    this.plane = this.curtains.addPlane(this.planeElement, this.planeParams);

    // if the plane was created successfully we can go on
    if(this.plane) {
        this.canvas = document.createElement("canvas");
        this.canvas.setAttribute("data-sampler", "canvasTexture");
        this.canvasContext = this.canvas.getContext("2d", { alpha: false });
      
        // load our canvas texture
        this.plane.loadCanvases([this.canvas]);

        // first we resize our mouse canvas
        this.resize();

        // then we handle the plane
        this.handlePlane();
    }
}


window.onload = function() {
    // init everything
    var mouseEffect = new MouseEffect(params);

    // if there's an error during the WebGL context creation
    mouseEffect.curtains.onerror(function() {
        document.body.classList.add("no-webgl");
    });

    // add the plane to start the effect
    mouseEffect.addPlane();
}