diff --git a/demo/btree.html b/demo/btree.html
new file mode 100644
index 0000000000000000000000000000000000000000..c23a7de52ee3215be73221be0c8e911127d6359b
--- /dev/null
+++ b/demo/btree.html
@@ -0,0 +1,87 @@
+<!doctype html>
+<html>
+ <head>
+ <meta charset="utf-8">
+ <title>CodeMirror: B-Tree visualization</title>
+ <link rel="stylesheet" href="../lib/codemirror.css">
+ <script src="../lib/codemirror.js"></script>
+ <link rel="stylesheet" href="../doc/docs.css">
+
+ <style type="text/css">
+ .lineblock { display: inline-block; margin: 1px; height: 5px; }
+ .CodeMirror {border: 1px solid #aaa; height: 400px}
+ </style>
+ </head>
+ <body>
+ <h1>CodeMirror: B-Tree visualization</h1>
+
+ <p>Shows a visual representation of the b-tree that CodeMirror
+ uses to store its document. See
+ the <a href="http://marijnhaverbeke.nl/blog/codemirror-line-tree.html">corresponding
+ blog post</a> for a description of this format. The gray blocks
+ under each leaf show the lines it holds (with their width
+ representing the line height). Add and remove content to see how
+ the nodes are split and merged to keep the tree balanced.</p>
+
+ <div style="position: relative">
+ <div style="width: 60%; display: inline-block; vertical-align: top">
+ <form><textarea id="code" name="code">type here, see a summary of the document b-tree to the right</textarea></form>
+ </div>
+ <div style="display: inline-block; height: 402px; overflow-y: auto" id="output"></div>
+ </div>
+
+ <script id="me">
+var editor = CodeMirror.fromTextArea(document.getElementById("code"), {
+ lineNumbers: true,
+ lineWrapping: true
+});
+var updateTimeout;
+editor.on("change", function(cm) {
+ clearTimeout(updateTimeout);
+ updateTimeout = setTimeout(updateVisual, 200);
+});
+updateVisual();
+
+function updateVisual() {
+ var out = document.getElementById("output");
+ out.innerHTML = "";
+
+ function drawTree(out, node) {
+ if (node.lines) {
+ out.appendChild(document.createElement("div")).innerHTML =
+ "<b>leaf</b>: " + node.lines.length + " lines, " + Math.round(node.height) + " px";
+ var lines = out.appendChild(document.createElement("div"));
+ lines.style.lineHeight = "6px"; lines.style.marginLeft = "10px";
+ for (var i = 0; i < node.lines.length; ++i) {
+ var line = node.lines[i], lineElt = lines.appendChild(document.createElement("div"));
+ lineElt.className = "lineblock";
+ var gray = Math.min(line.text.length * 3, 230), col = gray.toString(16);
+ if (col.length == 1) col = "0" + col;
+ lineElt.style.background = "#" + col + col + col;
+ console.log(line.height, line);
+ lineElt.style.width = Math.max(Math.round(line.height / 3), 1) + "px";
+ }
+ } else {
+ out.appendChild(document.createElement("div")).innerHTML =
+ "<b>node</b>: " + node.size + " lines, " + Math.round(node.height) + " px";
+ var sub = out.appendChild(document.createElement("div"));
+ sub.style.paddingLeft = "20px";
+ for (var i = 0; i < node.children.length; ++i)
+ drawTree(sub, node.children[i]);
+ }
+ }
+ drawTree(out, editor.view.doc);
+}
+
+function fillEditor() {
+ var sc = document.getElementById("me");
+ var doc = (sc.textContent || sc.innerText || sc.innerHTML).replace(/^\s*/, "") + "\n";
+ doc += doc; doc += doc; doc += doc; doc += doc; doc += doc; doc += doc;
+ editor.setValue(doc);
+}
+ </script>
+
+<p><button onclick="fillEditor()">Add a lot of content</button></p>
+
+ </body>
+</html>
diff --git a/index.html b/index.html
index feb15121af393a0a2f546c6d010f3c03d78374a4..5e7257d03a994ac0da005044f39e0ec31754b66b 100644
--- a/index.html
+++ b/index.html
@@ -116,6 +116,7 @@
<li><a href="demo/vim.html">Vim keybindings</a></li>
<li><a href="demo/closetag.html">Automatic xml tag closing</a></li>
<li><a href="demo/loadmode.html">Lazy mode loading</a></li>
+ <li><a href="demo/btree.html">Document tree visualization</a></li>
</ul>
<h2>Real-world uses:</h2>