VBoxLayout with multiple QLabels in a scrollarea some 'header' labels have a gradient background

As the scrollarea is scrolled a few pixels at a time the gradient is drawn and scaled to fill the newly exposed clip-rect only.

If the area is resized then the gradient is drawn correctly

Expected to see:

The same visual effect whether I scrolled down or expanded the window down (given no stretch)

Assuming the widget has a gradient:

1234567890

If I position the widget to clip the right 25% to get

1234567|

If I scroll in such a way as to expose the right 25% of the widget, I expect the gradient colours from 0.75-1.0 to be used to fill the rightmost 25% of the widget and to get:

01234567890

Got instead:

Clip-artefacts: the newly exposed area is filled using the full gradient
If I position the widget to clip the right 25% I get

1234567|

If I now scroll in such a way as to expose the right 25% of the widget, I get the gradient colours from 0 - 1.0 used to fill the rightmost 25% of the widget. This means I get:

01234567159

To see:

1 size the window large to see the entire widgets

2 resize the window to clip the shaded widgets. The gradient is redrawn to the visible object.

3 resize the window to clip the shaded widgets horizontally by 20%

4 scroll by clicking in the 'trough', not by dragging the slider. The newly exposed rectangle has the complete gradient.

5 drag scrolling produces unpleasant lines.

Example program:

#include <QApplication>
#include <QScrollArea>
#include <QLabel>
#include <QVBoxLayout>
#include <QPalette>
#include <QLinearGradient>

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

QScrollArea sa;
QWidget c;
QVBoxLayout box(&c);

QPalette pal = sa.palette();
pal.setColor(QPalette::WindowText, QColor(255,255,255));
QLinearGradient bgGrad = QLinearGradient(0,0,1,1);
bgGrad.setCoordinateMode(QGradient::ObjectBoundingMode);
// bgGrad.setCoordinateMode(QGradient::StretchToDeviceMode);
bgGrad.setColorAt(0.0, QColor("red"));
bgGrad.setColorAt(1.0, QColor("green"));
pal.setBrush(QPalette::Window, bgGrad);

QLabel *l;

for(int i=0;++i<10

{ l = new QLabel("FrederickFrederickFrederickFrederickFrederickFrederickFrederick\nFrederickFrederickFrederickFrederickFrederick\nFrederickFrederickFrederickFrederickFrederickFrederickFrederickFrederick\nFrederickFrederickFrederickFrederick"); l->setAutoFillBackground(true); l->setPalette(pal); box.addWidget(l); box.addWidget(new QLabel("DavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavid\nDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavidDavid")); }

sa.setWidget(&c);
sa.show();
return app.exec();
}