Regression in Q3Table scrolling performance

When scrolling a large Q3Table, the scrolling performance slows down the more items are visible in the table's viewport. The performance can easily degrade to scrolling one or two items (or less) per second, making it very time consuming to scroll a larger table.

The following example demonstrates the problem:

#include <QApplication>
#include <Q3Table>

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

Q3Table table(500, 20, 0);

for(int row = 0; row < table.numRows(); ++row) {
for(int col = 0; col < table.numCols(); ++col)

{ QString text("Cell %1 %2"); table.setText(row, col, text.arg(row).arg(col)); }

}

app.setMainWidget(&table);

table.showMaximized();

return app.exec();
}

This is a regression introduced with Qt 4.1's backingstore double buffering feature.