QwtPlotCurve draw it's full contents without using current zoom information

[Uwe]

Ok, i'm understand. Now it's works faster for smaller amount of points. Of course it's works SLOW for minimum zoom when user try to see all points

Check the archive of this forum for "levels of detail".

Using Douglas/Peucker you create ( in advance ) f.e 4 different sets of samples. Depending on the current zoom level one of these sets gets activated. Also enable polygon clipping.

Then you have the effect, that clipping ( the algo is fast ) - or/and your algorithm using the sample order - reduces the number of point when zooming deep and weeding for large scale ranges.

Uwe