On 2009-08-22 08:38+0100 Rochel, Alban wrote:
> Hello Alan,
>
> I am well aware that repaint is the bottleneck. What repaint does is
> ultimately to call QtPLWidget::plot() (via QtPLWidget::paintEvent()). Plot()
> does replay the whole buffer, it was never designed to be "region-aware". So
> no matter what region/rectangle is given to the overloaded repaint(...),
> everything would be redrawn.
>
> An easy way to fix that would be to allow it to draw within a QRegion mask
> only, using QPainter::clipRegion. And I believe this would improve
> performance. However, I think we can do better than this as:
> - The whole buffer would be unrolled anyway, only the actual painting would
> be clipped
> - we would have the overhead of updating the region at every line, polyline,
> polygon command received from PLplot.
>
> The solution I propose is to keep in memory an iterator ("pointer") to the
> last plotted element in the memory buffer, at each plot() call. This costs
> very little, and would allow to unroll and draw only the part of the buffer
> that has been added since the last flush(). No region merging, no clipping
> tests, just flushing what has not been flushed yet.
>
> I haven't tried any of the solutions yet and I may realise that my approach
> is not feasible or harder than I expect, but I believe this would be faster
> in the end.
>
Hi Alban:
Thanks for your patience with my question. Your explanation (with
QtPLWidget::plot replaced by QtPLWidget::doPlot) makes sense to me now.
Alan
__________________________
Alan W. Irwin
Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).
Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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