idian: Debounce widget repolishing

Uses Qt's QGlobalStatic macro to create a shared Utils singleton for
repolishing widgets. This means that multiple calls to the Utils'
styling class helpers only trigger a single repolish per widget during
a one tick of the Qt event loop.

shared/qt/idian/include/Idian/Utils.cpp

@@ -26,6 +26,38 @@
 #include <QStyleOptionFrame>
 
 namespace idian {
+Q_GLOBAL_STATIC(Utils, utils);
+
+Utils::Utils() : QObject(nullptr) {}
+
+void Utils::addToPolishQueue(QWidget *widget)
+{
+	widgetPolishQueue.push_back(widget);
+
+	if (isPolishPending) {
+		return;
+	}
+
+	isPolishPending = true;
+
+	QMetaObject::invokeMethod(this, &Utils::processPolishQueue, Qt::QueuedConnection);
+}
+
+void Utils::processPolishQueue()
+{
+	widgetPolishQueue.sort();
+	widgetPolishQueue.unique();
+
+	for (QPointer<QWidget> widget : widgetPolishQueue) {
+		if (widget) {
+			widget->style()->polish(widget);
+		}
+	}
+
+	isPolishPending = false;
+	widgetPolishQueue.clear();
+}
+
 void Utils::polishChildren(QWidget *widget)
 {
 	for (QWidget *child : widget->findChildren<QWidget *>()) {
@@ -35,7 +67,7 @@ void Utils::polishChildren(QWidget *widget)
 
 void Utils::repolish(QWidget *widget)
 {
-	widget->style()->polish(widget);
+	utils->addToPolishQueue(widget);
 }
 
 void Utils::addClass(QWidget *widget, const QString &classname)

shared/qt/idian/include/Idian/Utils.hpp

@@ -17,6 +17,7 @@
 
 #pragma once
 
+#include <QPointer>
 #include <QRegularExpression>
 #include <QStyle>
 #include <QWidget>
@@ -38,7 +39,12 @@ class Utils : public QObject {
 	}
 
 public:
-	Utils(QObject *parent = nullptr) {};
+	Utils();
+
+	bool isPolishPending{false};
+	std::list<QPointer<QWidget>> widgetPolishQueue;
+	void addToPolishQueue(QWidget *widget);
+	void processPolishQueue();
 
 	// Force all children widgets to repaint
 	static void polishChildren(QWidget *widget);