Create Crosshair Guide

{
  // Access current composition
  var comp = app.project.activeItem;
  if (comp && (comp instanceof CompItem)) {
    app.beginUndoGroup("Create Guide Layer");

    // Create a new shape layer
    var shapeLayer = comp.layers.addShape();
    shapeLayer.name = "Center Guide";

    // Set layer as guide layer
    shapeLayer.guideLayer = true;

    // Vertical Line
    var verticalLineGroup = shapeLayer.property("ADBE Root Vectors Group").addProperty("ADBE Vector Group");
    verticalLineGroup.name = "Vertical Line";
    var verticalPath = verticalLineGroup.property("ADBE Vectors Group").addProperty("ADBE Vector Shape - Group");
    var verticalPathData = verticalPath.property("ADBE Vector Shape").value;
    verticalPathData.vertices = [[comp.width / 2, 0], [comp.width / 2, comp.height]];
    verticalPath.property("ADBE Vector Shape").setValue(verticalPathData);
    var verticalStroke = verticalLineGroup.property("ADBE Vectors Group").addProperty("ADBE Vector Graphic - Stroke");
    verticalStroke.property("ADBE Vector Stroke Color").setValue([1, 1, 1]);
    verticalStroke.property("ADBE Vector Stroke Width").setValue(2);

    // Horizontal Line
    var horizontalLineGroup = shapeLayer.property("ADBE Root Vectors Group").addProperty("ADBE Vector Group");
    horizontalLineGroup.name = "Horizontal Line";
    var horizontalPath = horizontalLineGroup.property("ADBE Vectors Group").addProperty("ADBE Vector Shape - Group");
    var horizontalPathData = horizontalPath.property("ADBE Vector Shape").value;
    horizontalPathData.vertices = [[0, comp.height / 2], [comp.width, comp.height / 2]];
    horizontalPath.property("ADBE Vector Shape").setValue(horizontalPathData);
    var horizontalStroke = horizontalLineGroup.property("ADBE Vectors Group").addProperty("ADBE Vector Graphic - Stroke");
    horizontalStroke.property("ADBE Vector Stroke Color").setValue([1, 1, 1]);
    horizontalStroke.property("ADBE Vector Stroke Width").setValue(2);

    // Slider Control for opacity
    var sliderControl = shapeLayer.property("ADBE Effect Parade").addProperty("ADBE Slider Control");
    sliderControl.name = "Opacity Control";
    sliderControl.property("Slider").setValue(100);
    var opacityProperty = shapeLayer.property("ADBE Transform Group").property("ADBE Opacity");
    opacityProperty.expression = 'effect("Opacity Control")("Slider")';

    // Set anchor point to center of layer
    var x_center = comp.width / 2;
    var y_center = comp.height / 2;
    shapeLayer.property("ADBE Transform Group").property("ADBE Anchor Point").setValue([x_center, y_center]);

    // Set layer position to center of composition
    shapeLayer.property("ADBE Transform Group").property("ADBE Position").setValue([x_center, y_center]);

    app.endUndoGroup();
  } else {
    alert("No active composition.");
  }
}