how to solve the limit of plot length

[baoxuefei771]

I have to draw a curve that maybe 6000 meters long,but when i draw the curve use qwt plot it can not draw it correctly
how should I do ? Thank you !!
You can see that part of the plot seems ok,but the rest part of the plot just black....

6492

[Uwe]

The black areas are covering the frames of the canvas - looks like there are some widgets that are layered on top of the canvas.

Check the widgets in your application ( for example dump the widget tree ) and try to find out which widgets are at these positions.

Also check the realtime example for using scrollbars. Using a scrollview like in your screenshot is not a good idea.

Uwe