MecLib GitHub issue no. 37: Grid lines to the background

MecLib GitHub issue no. 37: Grid lines to the background

by aaronamran

HTML

<script src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js"></script>
<script src="https://cdn.jsdelivr.net/npm/jsxgraph/distrib/jsxgraphcore.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/jsxgraph/distrib/jsxgraph.css">
<div id="jxgbox" class="jxgbox" style="width:500px; height:500px">
</div>
<p id="init">[
  [ "grid", "x","y", -1, 10, -2, 6, 40 ],
  [ "polygon", "name", [3, 1], [3, -1], [6, -1], [6, 1] ]
  ]
</p>
<p id="data"></p>
<p id="fbd_names"></p>

JavaScript

// Start of jsfiddle header.
var mode = "jsfiddle";
var divid = "jxgbox";
var fbd_names = "fbd_names";
var stateRef = "data";
var initstring = document.getElementById("init").innerHTML;
const centeredLabelStyle = {
  size: 0,
  showInfobox: false,
  label: {
    offset: [0, 0],
    anchorX: 'middle',
    anchorY: 'middle'
  }
};


// https://github.com/mkraska/meclib/wiki
// version info
const versionText= "JXG "+JXG.version+" Meclib 2023 08 16";
const highlightColor = "orange";
const movableLineColor = "blue";
const loadColor = "blue";
const defaultMecLayer = 6;
let pxunit = 1/40; // is reset by "grid"
let a = 16*pxunit; // is reset by "grid"
const deg2rad = Math.PI/180, rad2deg = 180/Math.PI;
const tolPointLine = 0.001;
let xscale = 1, yscale = 1; // default scale for infobox, can be modified by "grid"
let dpx = 1, dpy = 1; // default decimal precision for infobox, can be modified by "grid"
// infobox settings, further settings after board initiation
JXG.Options.infobox.layer = defaultMecLayer+5;
JXG.Options.infobox.strokeColor = 'black';
JXG.Options.infobox.cssStyle = 'background-color: #ffffffdd;'
// snap settings. Interactive objects are handled explicity
JXG.Options.point.snapToGrid = false; // grid snap spoils rotated static objects
JXG.Options.point.snapSizeX = 0.1;
JXG.Options.point.snapSizeY = 0.1;
// interactive objects are released explicitly
JXG.Options.point.fixed = true; 
JXG.Options.line.fixed = true; 
JXG.Options.circle.fixed = true;
// label settings
JXG.Options.text.useMathJax = true;
JXG.Options.text.parse = false;
JXG.Options.label.useMathJax = true;
JXG.Options.label.offset = [0, 0];
JXG.Options.label.anchorY = 'middle';
// suppress automatic labels
JXG.Options.point.name = ""; 
// highlighting is activated explicitly for interactive objects
JXG.Options.curve.highlight = false;
JXG.Options.label.highlight = false;
JXG.Options.text.highlight = false;
JXG.Options.circle.highlight = false;
JXG.Options.line.highlight =...