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HTML

              
                <canvas style="position: relative;" id= "canvas" width="300" height="600"></canvas>
              
            
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CSS

              
                
              
            
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JS

              
                (function () {
  var canvas = document.getElementById("canvas");
  canvas.style.cursor = "none"; // Hide cursor

  var ctx = canvas.getContext("2d");

  var width = canvas.width;
  var height = canvas.height;

  var updateCanvas = function (mousePosition) {
    var imgData = ctx.getImageData(0, 0, width, height);
    var data = imgData.data;
    // Update the data array
    for (var x = 0; x < width; x++) {
      for (var y = 0; y < height; y++) {
        var index = (y * width + x) * 4;

        var distanceToMouse = Math.sqrt(
          (mousePosition.x - x) * (mousePosition.x - x) +
            (mousePosition.y - y) * (mousePosition.y - y)
        );
        distanceToMouse = parseInt(distanceToMouse); // Round, throwing away all decimals
        if (distanceToMouse < 1) {
          distanceToMouse = 1; // Avoid division by 0 here
        }

        var color = (25 / distanceToMouse) * 255;
        color = parseInt(color); // Round again

        data[index + 0] = color; // Red
        data[index + 1] = color; // Green
        data[index + 2] = color; // Blue
        data[index + 3] = 255; // Alpha (transparency)
      }
    }

    // Overwrite the canvas with the updated data array
    ctx.putImageData(imgData, 0, 0);
  };

  updateCanvas({ x: width / 2, y: height / 2 }); // Ensures something drawn on load

  canvas.addEventListener("mousemove", function (e) {
    var mousePosition = { x: e.layerX, y: e.layerY };
    updateCanvas(mousePosition);
  });
})();

              
            
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999px

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