Index: binaries/data/mods/mod/gui/common/ResizeBar.js
===================================================================
--- /dev/null
+++ binaries/data/mods/mod/gui/common/ResizeBar.js
@@ -0,0 +1,269 @@
+// See lobby_autociv.js init function for examples
+function ResizeBar(object, side, width, objectsHooked, isVisibleCondition, onDragDown)
+{
+	this.object = this.parseObject(object);
+	this.side = side;
+	this.halfWidth = width === undefined ?
+		ResizeBar.defaults.width / 2.0 :
+		width / 2.0;
+
+	this.objectsHooked = objectsHooked ? objectsHooked : [];
+	this.isVisibleCondition = isVisibleCondition ?
+		isVisibleCondition :
+		() => !this.object.hidden;
+
+	this.onDragDown = onDragDown ? onDragDown : () => { };
+
+	this.lastIn = false;
+	this.dragging = false;
+
+	for (let i = 0; i < this.objectsHooked.length; ++i)
+		this.objectsHooked[i][0] = this.parseObject(this.objectsHooked[i][0]);
+}
+
+ResizeBar.mouse = {
+	"x": 0,
+	"y": 0,
+	"set": function (mouse) { [this.x, this.y] = [mouse.x, mouse.y]; }
+};
+
+ResizeBar.mousePress = Object.assign({}, ResizeBar.mouse);
+
+ResizeBar.mouseRelease = Object.assign({}, ResizeBar.mouse);
+
+ResizeBar.dragging = false;
+
+ResizeBar.defaults = { "width": 14 };
+
+ResizeBar.prototype.parseObject = function (object)
+{
+	return typeof object == "string" ?
+		Engine.GetGUIObjectByName(object) :
+		object;
+};
+
+ResizeBar.prototype.mouseInside = function ()
+{
+	if (!this.isVisibleCondition())
+		return false;
+
+	let rect = this.object.getComputedSize();
+	switch (this.side)
+	{
+		case "left": case "right":
+			return Math.abs(rect[this.side] - ResizeBar.mouse.x) <= this.halfWidth &&
+				rect.top + this.halfWidth < ResizeBar.mouse.y &&
+				rect.bottom - this.halfWidth > ResizeBar.mouse.y;
+		case "top": case "bottom":
+			return Math.abs(rect[this.side] - ResizeBar.mouse.y) <= this.halfWidth &&
+				rect.left + this.halfWidth < ResizeBar.mouse.x &&
+				rect.right - this.halfWidth > ResizeBar.mouse.x;
+		default:
+			warn(`No side by name: "${this.side}"\n` + Error().stack);
+	}
+};
+
+ResizeBar.prototype.sideC = function (side)
+{
+	switch (side ? side : this.side)
+	{
+		case "left": return "right";
+		case "right": return "left";
+		case "top": return "bottom";
+		case "bottom": return "top";
+	}
+};
+
+ResizeBar.prototype.sideO = function (side)
+{
+	switch (side ? side : this.side)
+	{
+		case "left": return "top";
+		case "right": return "bottom";
+		case "top": return "left";
+		case "bottom": return "right";
+	}
+};
+
+ResizeBar.prototype.sideX = function (side)
+{
+	return this.sideC(this.sideO());
+};
+
+ResizeBar.prototype.sideSign = function (side)
+{
+	switch (side ? side : this.side)
+	{
+		case "right":
+		case "bottom": return +1;
+		default: return -1;
+	}
+};
+
+ResizeBar.prototype.sideMouse = function (side)
+{
+	switch (side ? side : this.side)
+	{
+		case "left":
+		case "right": return "x";
+		default: return "y";
+	}
+};
+
+ResizeBar.prototype.viewResizeBar = function ()
+{
+	let absPos = this.object.getComputedSize();
+
+	let iSize = GUISize();
+	iSize[this.side] = absPos[this.side];
+	iSize[this.sideC()] = absPos[this.side];
+	iSize[this.sideO()] = absPos[this.sideO()];
+	iSize[this.sideX()] = absPos[this.sideX()];
+
+	let fSize = Object.assign({}, iSize); // Copy
+	fSize[this.side] = iSize[this.side] + this.sideSign() * this.halfWidth;
+	fSize[this.sideC()] = iSize[this.side] - this.sideSign() * this.halfWidth;
+
+	animateObject(ResizeBar.bar, {
+		"onStart": bar =>
+		{
+			bar.size = iSize;
+			bar.hidden = false;
+		},
+		"size": fSize
+	});
+};
+
+ResizeBar.prototype.hideResizeBar = function ()
+{
+	let iSize = ResizeBar.bar.size;
+	let centerPos = (iSize[this.side] + iSize[this.sideC()]) * 0.5;
+	iSize[this.side] = centerPos;
+	iSize[this.sideC()] = centerPos;
+
+	animateObject(ResizeBar.bar, {
+		"size": iSize,
+		"onComplete": bar => bar.hidden = true
+	});
+};
+
+ResizeBar.prototype.tick = function ()
+{
+	if (!ResizeBar.dragging)
+	{
+		let currentIn = this.mouseInside();
+		// double check needed for bars intersection case (first added will have priority)
+		if (this.lastIn == currentIn && !ResizeBar.bar.hidden) return;
+		if (currentIn) this.viewResizeBar();
+		else this.hideResizeBar();
+		this.lastIn = currentIn;
+		return currentIn;
+	}
+	else if (this.dragging)
+	{
+		let size = ResizeBar.bar.size;
+		size[this.side] = ResizeBar.mouse[this.sideMouse()] + this.sideSign() * this.halfWidth;
+		size[this.sideC()] = ResizeBar.mouse[this.sideMouse()] - this.sideSign() * this.halfWidth;
+		ResizeBar.bar.size = size;
+	}
+};
+
+ResizeBar.prototype.dragUp = function ()
+{
+	if (!this.mouseInside())
+		return false;
+
+	ResizeBar.mousePress.set(ResizeBar.mouse);
+	ResizeBar.dragging = true;
+	this.dragging = true;
+	return true;
+};
+
+ResizeBar.prototype.dragDown = function ()
+{
+	if (!this.dragging)
+		return false;
+
+	ResizeBar.mouseRelease.set(ResizeBar.mouse);
+
+	let displacement = ResizeBar.mouseRelease[this.sideMouse()] - ResizeBar.mousePress[this.sideMouse()];
+	if (displacement)
+	{
+		animateObject(
+			this.object,
+			{
+				"size": { [this.side]: this.object.size[this.side] + displacement },
+				"onComplete": this.onDragDown
+			}
+		);
+		for (let [object, side] of this.objectsHooked)
+			animateObject(
+				object,
+				{ "size": { [side]: object.size[side] + displacement } }
+			);
+	}
+
+	ResizeBar.dragging = false;
+	this.dragging = false;
+	return true;
+};
+
+
+var resizeBar = function (object, side, width, objectsHooked, isVisibleCondition, onDragDown)
+{
+	resizeBar.list.push(new ResizeBar(object, side, width, objectsHooked, isVisibleCondition, onDragDown));
+};
+
+resizeBar.list = [];
+
+resizeBar.onEvent = function (event)
+{
+	if (resizeBar.firstTick)
+		return;
+
+	switch (event.type)
+	{
+		case "mousebuttondown":
+			for (let bar of resizeBar.list)
+				if (bar.dragUp()) break;
+			break;
+		case "mousebuttonup":
+			for (let bar of resizeBar.list)
+				if (bar.dragDown()) break;
+			break;
+		case "mousemotion":
+			ResizeBar.mouse.set(event)
+			break;
+	}
+}
+
+resizeBar.firstTick = true;
+
+resizeBar.onTick = function ()
+{
+	// Don't process anything at the first tick (error otherwise)
+	switch (resizeBar.firstTick)
+	{
+		case true:
+			resizeBar.firstTick = false;
+			ResizeBar.bar = Engine.GetGUIObjectByName("glResizeBar");
+			break;
+		default:
+			for (let bar of resizeBar.list)
+				if (bar.tick()) break;
+	}
+}
+
+/* THIS NEEDS TO BE ADDED ON FILES WHERE YOU WANT TO USE IT
+
+    function handleInputBeforeGui(ev)
+    {
+        resizeBar.onEvent(ev);
+        return false;
+    }
+
+    function onTick(){
+        resizeBar.onTick();
+    }
+
+*/