A frameless Window with opacity animation turns black at the end of animation.

#include <QApplication>
#include <QPushButton>
#include <QHBoxLayout>
#include <QPropertyAnimation>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	// Create transparent popup window.
	QWidget* popup = new QWidget(NULL, Qt::WindowFlags(Qt::FramelessWindowHint | Qt::ToolTip));
	popup->setWindowFlags(Qt::FramelessWindowHint | Qt::ToolTip);
	popup->setAttribute(Qt::WA_TranslucentBackground);

	// Add button to popup window.
	QHBoxLayout* layout = new QHBoxLayout(popup);
	QPushButton* button1 = new QPushButton(popup);
	button1->setFixedSize(200, 300);
	layout->addWidget(button1);
	QPushButton* button2 = new QPushButton(popup);
	button2->setFixedSize(200, 300);
	layout->addWidget(button2);

	// Create opacity animation.
	QPropertyAnimation* fadeInAnimation = new QPropertyAnimation(popup, "windowOpacity");
	fadeInAnimation->setDuration(1000);
	fadeInAnimation->setStartValue(0.0);
	fadeInAnimation->setEndValue(1.0);

	// Show popup
	popup->setWindowOpacity(0.0);
	fadeInAnimation->start();
	popup->show();

	return a.exec();
}