From 61be09d54ada3e6438a86485ec08aeb3cef220ca Mon Sep 17 00:00:00 2001
From: Jeff Parsons <jeff@pcjs.org>
Date: Mon, 2 Jan 2017 22:17:12 -0800
Subject: [PATCH] Minimal support for "sticky" machines (ie, machines that
 can't be scrolled off the top of the page)

---
 modules/shared/es6/sticky.js | 84 ++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 modules/shared/es6/sticky.js

diff --git a/modules/shared/es6/sticky.js b/modules/shared/es6/sticky.js
new file mode 100644
index 000000000..a4e0615dc
--- /dev/null
+++ b/modules/shared/es6/sticky.js
@@ -0,0 +1,84 @@
+/**
+ * @fileoverview Support for "sticky" machines
+ * @author <a href="mailto:Jeff@pcjs.org">Jeff Parsons</a> (@jeffpar)
+ * @copyright © Jeff Parsons 2012-2017
+ *
+ * This file is part of PCjs, a computer emulation software project at <http://pcjs.org/>.
+ *
+ * PCjs is free software: you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation, either version 3
+ * of the License, or (at your option) any later version.
+ *
+ * PCjs is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
+ * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with PCjs.  If not,
+ * see <http://www.gnu.org/licenses/gpl.html>.
+ *
+ * You are required to include the above copyright notice in every modified copy of this work
+ * and to display that copyright notice when the software starts running; see COPYRIGHT in
+ * <http://pcjs.org/modules/shared/lib/defines.js>.
+ *
+ * Some PCjs files also attempt to load external resource files, such as character-image files,
+ * ROM files, and disk image files. Those external resource files are not considered part of PCjs
+ * for purposes of the GNU General Public License, and the author does not claim any copyright
+ * as to their contents.
+ */
+
+"use strict";
+
+/**
+ * addStickYMachine(idMachine)
+ *
+ * @param {string} idMachine
+ */
+function addStickyMachine(idMachine)
+{
+    var machine = document.getElementById(idMachine);
+    if (machine) {
+        var machineFooter = document.getElementById(idMachine + '.footer');
+        if (machineFooter) {
+            var topMachine = findTop(machine);
+            var prevOnScroll = window.onscroll;
+            window.onscroll = function() {
+                if (window.pageYOffset <= topMachine) {
+                    machine.style.position = 'relative';
+                    machine.style.zIndex = 'auto';
+                    machine.style.backgroundColor = '';
+                    machine.style.paddingRight = 0;
+                    if (machineFooter) machineFooter.style.paddingTop = 0;
+                } else {
+                    machine.style.position = 'fixed';
+                    machine.style.zIndex = 1;
+                    machine.style.backgroundColor = 'white';
+                    machine.style.paddingRight = '30px';
+                    machine.style.top = 0;
+                    if (machineFooter) machineFooter.style.paddingTop = machine.offsetHeight + 'px';
+                }
+            };
+            if (prevOnScroll) prevOnScroll();
+        }
+    }
+}
+
+/**
+ * findTop(obj)
+ *
+ * @param {Object} obj
+ */
+function findTop(obj)
+{
+    var curTop = 0;
+    if (typeof obj.offsetParent != 'undefined' && obj.offsetParent) {
+        while (obj.offsetParent) {
+            curTop += obj.offsetTop;
+            obj = obj.offsetParent;
+        }
+        curTop += obj.offsetTop;
+    }
+    else if (obj.y) {
+        curTop += obj.y;
+    }
+    return curTop;
+}