Draw a bar chart inisde the QScrollArea

[ultrasonic]

Hi,

I am writing a program which reads lots of data (more than 1000) and show them by drawing a bar chart. I subclassed QWidget , reimplemented paintEvent() to draw my chart and called QScrollArea::setWidget() to setup the chart into the QScrollArea. But when I dragged the scroll bar in the QScrollArea, the scrollbar and chart moved extremely slowly. How do I resolve the problem?

Here is my source code.