Method paintEvent

src/3rdparty/Qt-Advanced-Docking-System/src/DockOverlay.cpp:608–651

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//============================================================================
void CDockOverlay::paintEvent(QPaintEvent* event)
{
	Q_UNUSED(event);

	// Draw rect based on location
	if (!d->DropPreviewEnabled)
	{
		d->DropAreaRect = QRect();
		return;
	}

	QRect r = rect();
	const DockWidgetArea da = dropAreaUnderCursor();
	double Factor = (CDockOverlay::ModeContainerOverlay == d->Mode) ?
		3 : 2;

	switch (da)
	{
    case TopDockWidgetArea: r.setHeight(r.height() / Factor); break;
	case RightDockWidgetArea: r.setX(r.width() * (1 - 1 / Factor)); break;
	case BottomDockWidgetArea: r.setY(r.height() * (1 - 1 / Factor)); break;
	case LeftDockWidgetArea: r.setWidth(r.width() / Factor); break;
	case CenterDockWidgetArea: r = rect();break;
	case LeftAutoHideArea: r.setWidth(d->sideBarOverlaySize(SideBarLeft)); break;
	case RightAutoHideArea: r.setX(r.width() - d->sideBarOverlaySize(SideBarRight)); break;
	case TopAutoHideArea: r.setHeight(d->sideBarOverlaySize(SideBarTop)); break;
	case BottomAutoHideArea: r.setY(r.height() - d->sideBarOverlaySize(SideBarBottom)); break;
	default: return;
	}

	QPainter painter(this);
    QColor Color = palette().color(QPalette::Active, QPalette::Highlight);
    QPen Pen = painter.pen();
    Pen.setColor(Color.darker(120));
    Pen.setStyle(Qt::SolidLine);
    Pen.setWidth(1);
    Pen.setCosmetic(true);
    painter.setPen(Pen);
    Color = Color.lighter(130);
    Color.setAlpha(64);
    painter.setBrush(Color);
	painter.drawRect(r.adjusted(0, 0, -1, -1));
	d->DropAreaRect = r;
}


//============================================================================