MathToys/multiplication_strings.html at master · jennselby/MathToys · GitHub

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<!doctype html>
<html>

<head>
    <meta charset='utf-8'>
</head>

<body>
    <canvas id='strings' width='650px' height='650px'></canvas>
    <div style="float: right">
        <div>
            <label for='numDots'>Number of Dots</label>
            <input type='number' id='numDots'>
            <label for='numDotChange'>Change By</label>
            <input type='number' id='numDotChange'>
        </div>
        <div>
            <label for='multFactor'>Multiplication Factor</label>
            <input type='number' id='multFactor'>
            <label for='multFactorChange'>Change By</label>
            <input type='number' id='multFactorChange'>
        </div>
        <div>
            <input type='button' id='startPause' value='Start'>
            <input type='button' id='reset' value='Reset'>
        </div>
    </div>

    <script>
        var canvas = document.getElementById('strings');
        var context = canvas.getContext('2d');
        context.font = '8pt Sans-Serif';
        context.textAlign = 'center';


        var CENTER_X = canvas.width/2;
        var CENTER_Y = canvas.height/2;
        var RADIUS = Math.min(canvas.width, canvas.height)/2 - 25;

        var timerId;

        function resetSettings () {
            settings = {
                multFactor: 2,
                multFactorChange: 0,
                numDots: 20,
                numDotChange: 0,
            };
            document.getElementById('multFactor').value = settings.multFactor;
            document.getElementById('multFactorChange').value = settings.multFactorChange;
            document.getElementById('numDots').value = settings.numDots;
            document.getElementById('numDotChange').value = settings.numDotChange;

        }

        function startAnimation() {
            timerId = window.setInterval(updateStrings, 250);

            var button = document.getElementById('startPause');
            button.removeEventListener('click', startAnimation);
            button.addEventListener('click', pauseAnimation);
            button.value = 'Pause';
        }

        function pauseAnimation() {
            window.clearInterval(timerId);

            var button = document.getElementById('startPause');
            button.removeEventListener('click', pauseAnimation);
            button.addEventListener('click', startAnimation);
            button.value = 'Start';
        }

        function drawCircle() {
            context.beginPath();
            context.arc(CENTER_X, CENTER_Y, RADIUS, 0, 2 * Math.PI);
            context.strokeStyle = '#0000ff';
            context.stroke();
        }

        function drawDots() {
            var numDots = settings.numDots;
            var angleIncrement = 2 * Math.PI / numDots;
            context.fillStyle = '#000000';

            for (index = 0; index < numDots; ++index) {
                var x = RADIUS * Math.cos(2 * Math.PI - angleIncrement * index);
                var y = RADIUS * Math.sin(2 * Math.PI - angleIncrement * index);

                context.beginPath();
                context.arc(x + CENTER_X, y + CENTER_Y, 5, 0, 2 * Math.PI);
                context.fill();
                context.fillText(index, x * 1.05 + CENTER_X, y * 1.05 + CENTER_Y);
            }
        }

        function drawStrings() {
            var numDots = settings.numDots;
            var angleIncrement = 2 * Math.PI / numDots;

            context.beginPath();
            for (index = 0; index < numDots; ++index) {
                var x = RADIUS * Math.cos(2 * Math.PI - angleIncrement * index) + CENTER_X;
                var y = RADIUS * Math.sin(2 * Math.PI - angleIncrement * index) + CENTER_Y;

                var newIndex = index * settings.multFactor;
                while (newIndex >= numDots) {
                    newIndex -= numDots;
                }
                var newX = RADIUS * Math.cos(2 * Math.PI - angleIncrement * newIndex) + CENTER_X;
                var newY = RADIUS * Math.sin(2 * Math.PI - angleIncrement * newIndex) + CENTER_Y;

                context.moveTo(x, y);
                context.lineTo(newX, newY);
            }
            context.strokeStyle = '#0000ff';
            context.stroke();
        }

        function drawAll() {
            context.clearRect(0, 0, canvas.width, canvas.height);
            drawCircle();
            drawDots();
            drawStrings();
        }

        function updateStrings() {
            if (settings.multFactorChange == 0 && settings.numDotChange == 0) {
                // nothing to do
                return;
            }

            settings.multFactor += settings.multFactorChange;
            document.getElementById('multFactor').value = settings.multFactor;

            settings.numDots += settings.numDotChange;
            document.getElementById('numDots').value = settings.numDots;

            drawAll();
        }

        // initialize settings in the code and in the HTML input elements
        resetSettings();

        // Update settings when their corresponding input box changes
        for (setting in settings) {
            document.getElementById(setting).addEventListener(
                'change',
                function() {
                    var setting = this.id;
                    var newValue = this.value;

                    if (setting.substring(0, 6) == 'numDot') {
                        newValue = parseInt(newValue);
                    }
                    else {
                        newValue = parseFloat(newValue);
                    }

                    if (newValue != NaN) {
                        settings[setting] = newValue;
                        drawAll();
                    }
                }
            );
        }

        document.getElementById('reset').addEventListener(
            'click',
            function() {
                resetSettings();
                drawAll();
            }
        );
        document.getElementById('startPause').addEventListener('click', startAnimation);

        drawAll();
    </script>
</body>

</html>