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                <canvas style="position: relative;" id="canvas" width="300" height="250">




                var canvas = document.getElementById("canvas");

// Grab the pixel data
var width = canvas.width;
var height = canvas.height;

var ctx = canvas.getContext("2d");
var imgData = ctx.getImageData(0, 0, width, height);
var 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 isPointOnLine = x == y;
            data[index + 0] = 144; // Red
            data[index + 1] = 90; // Green
            data[index + 2] = 90; // Blue
            data[index + 3] = 255; // Alpha (transparency)
            data[index + 0] = 90; // Red
            data[index + 1] = 144; // Green
            data[index + 2] = 90; // Blue
            data[index + 3] = 255; // Alpha (transparency)

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