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Content preview: On 9/25/19 10:58 PM, André Pönitz wrote: > Is drawing the
grid so expensive that you can't simply do that on > each update of the
"lower
levels"? I don't know about the specific situation of Israel, but a grid
is often made of dotted lines and in oscilloscope alike situations it is not
unlikely to be more expensive, than drawing the curve - if it is a solid
line of not too many points. [...]
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--- Begin Message ---
On 9/25/19 10:58 PM, André Pönitz wrote:
Is drawing the grid so expensive that you can't simply do that on
each update of the "lower levels"?
I don't know about the specific situation of Israel, but a grid is often
made of dotted lines and in oscilloscope alike situations it is not
unlikely to be more expensive, than drawing the curve - if it is a solid
line of not too many points.
So yes having to redraw the grid with each frame can be a bottleneck for
plot widgets.
I did not check the code of the QGraphicsView framework since quite
some time, but IIRC correctly it "renders" before clipping - like Qt
does in general. So in situations where you zoom in deep and the
coordinates of some lines reach far out the visible area it can become
a significant factor.
I remember that in the early Qt4 days I was running into situations,
where rendering a grid took minutes(!) for a zoomed-in polar
plot ( https://qwtpolar.sourceforge.io/ ). The time was spent on
calculating millions of dots that were far outside the visible area.
It might be more than 10 years ago since I suggested adding a
ClipPolygon flag to the QPainter renderHints, without having much
success. This is why Qwt always manually clips before calling QPainter
methods.
Uwe
--- End Message ---
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