I want to draw a line whenever new data comes .

I am trying to paint only particular area where new line should be drawn so i am using update(QRect).

but i can see line drawn or painting is also happening slightly before rect x start point .

since update(QRectF) support is not there it is rounding off to near by int value ,because of that we see this problem .

Can anybody help how to over come this problem ?
Any sample code with update(rect) ?
can i draw a line inside update(rect) area ?

thx in advance