Create an Arc with Specified Number of Anchor Points – Illustrator Script

// Script to create a smooth arc with a specified number of anchor points and integrated UI options, centered in the document.
function drawSmoothArc(numAnchors, radius, startAngle, endAngle) {
    if (numAnchors < 2) {
        alert("Please specify at least 2 anchor points for a smooth arc.");
        return;
    }

    // Convert start and end angles from degrees to radians
    var startRad = startAngle * Math.PI / 180;
    var endRad = endAngle * Math.PI / 180;
    var arcAngle = endRad - startRad;

    // Get the active document and artboard dimensions for centering the arc.
    var doc = app.activeDocument;
    var activeAB = doc.artboards[doc.artboards.getActiveArtboardIndex()];
    var abRect = activeAB.artboardRect; // [left, top, right, bottom]
    var centerX = (abRect[0] + abRect[2]) / 2;
    var centerY = (abRect[1] + abRect[3]) / 2;

    // Calculate handle length dynamically based on the arc segment
    var theta = arcAngle / (numAnchors - 1); // Angle step between points
    var handleLength = radius * 4 / 3 * (1 - Math.cos(theta / 2)) / Math.sin(theta / 2);

    // Start a new document if no document is open
    if (app.documents.length === 0) {
        doc = app.documents.add();
        // Recalculate center after creating a new document using default artboard
        activeAB = doc.artboards[doc.artboards.getActiveArtboardIndex()];
        abRect = activeAB.artboardRect;
        centerX = (abRect[0] + abRect[2]) / 2;
        centerY = (abRect[1] + abRect[3]) / 2;
    }

    // Create a new layer for the arc
    var arcLayer = doc.layers.add();
    arcLayer.name = "Smooth Arc";

    // Create a new path for the arc
    var arcPath = arcLayer.pathItems.add();
    arcPath.stroked = true;
    arcPath.strokeColor = new RGBColor();
    arcPath.strokeColor.red = 0;
    arcPath.strokeColor.green = 0;
    arcPath.strokeColor.blue = 0;
    arcPath.filled = false;

    // Calculate and add each anchor point along the arc
    for (var i = 0; i < numAnchors; i++) {
        var angle = startRad + i * theta;

        // Anchor point position
        var x = centerX + radius * Math.cos(angle);
        var y = centerY + radius * Math.sin(angle);

        // In and out handles for smoothness
        var inHandleX = x - handleLength * Math.cos(angle + Math.PI / 2);
        var inHandleY = y - handleLength * Math.sin(angle + Math.PI / 2);
        var outHandleX = x + handleLength * Math.cos(angle + Math.PI / 2);
        var outHandleY = y + handleLength * Math.sin(angle + Math.PI / 2);

        // Add anchor point with handles
        var point = arcPath.pathPoints.add();
        point.anchor = [x, y];
        point.leftDirection = [inHandleX, inHandleY];
        point.rightDirection = [outHandleX, outHandleY];
        point.pointType = PointType.SMOOTH;
    }

    // Ensure the arc is open by not setting it as closed
    arcPath.closed = false;
}

function showUIDialog() {
    // Create a new dialog window
    var dlg = new Window('dialog', 'Draw Smooth Arc');
    dlg.alignChildren = 'fill';

    // Panel for input settings
    var inputPanel = dlg.add('panel', undefined, 'Settings');
    inputPanel.orientation = 'column';
    inputPanel.alignChildren = 'left';
    inputPanel.margins = 15;

    // Number of Anchor Points
    inputPanel.add('statictext', undefined, 'Number of Anchor Points:');
    var numAnchorsInput = inputPanel.add('edittext', undefined, '6');
    numAnchorsInput.characters = 10;

    // Radius
    inputPanel.add('statictext', undefined, 'Radius:');
    var radiusInput = inputPanel.add('edittext', undefined, '100');
    radiusInput.characters = 10;

    // Start Angle
    inputPanel.add('statictext', undefined, 'Start Angle (degrees):');
    var startAngleInput = inputPanel.add('edittext', undefined, '0');
    startAngleInput.characters = 10;

    // End Angle
    inputPanel.add('statictext', undefined, 'End Angle (degrees):');
    var endAngleInput = inputPanel.add('edittext', undefined, '180');
    endAngleInput.characters = 10;

    // Button Group
    var btnGroup = dlg.add('group');
    btnGroup.alignment = 'center';
    var okBtn = btnGroup.add('button', undefined, 'OK', {name:'ok'});
    var cancelBtn = btnGroup.add('button', undefined, 'Cancel', {name:'cancel'});

    // On OK button click
    okBtn.onClick = function() {
        // Parse input values to numbers
        var numAnchors = parseInt(numAnchorsInput.text, 10);
        var radius = parseFloat(radiusInput.text);
        var startAngle = parseFloat(startAngleInput.text);
        var endAngle = parseFloat(endAngleInput.text);

        if (isNaN(numAnchors) || numAnchors < 2) {
            alert("Please enter a valid number for anchor points (at least 2).");
            return;
        }
        if (isNaN(radius) || radius <= 0) {
            alert("Please enter a valid positive number for radius.");
            return;
        }
        if (isNaN(startAngle) || isNaN(endAngle)) {
            alert("Please enter valid numbers for angles.");
            return;
        }

        dlg.close();
        drawSmoothArc(numAnchors, radius, startAngle, endAngle);
    };

    // Cancel button to close the dialog without running the script
    cancelBtn.onClick = function() {
        dlg.close();
    };

    dlg.center();
    dlg.show();
}

// Run the UI dialog
showUIDialog();