[kde-edu]: KDE/kdeedu/libkdeedu/kdeeduplot

Benoît Jacob jacob at math.jussieu.fr
Sun Oct 29 09:00:53 CET 2006

Great work Jason!
Thanks a lot for having implemented this.

Le dimanche 29 octobre 2006 04:25, Jason Harris a écrit :
> SVN commit 599914 by harris:
> Implementing non-colliding text labels in kdeeduplot, based on kmplot
> code.
> It works, but it could probably be faster.  You don't need to know
> anything about it to use the feature, it all happens behind the scenes.
> Just add some items with labels and enjoy the magic.
> However, in the interest of inspiring optimization, here's a brief
> description of how it works:
> KPlotWidget now has a private array of floats: PlotMask[100][100].
> This is a rough division of the content of the plot into a 100x100
> grid.  Where the plot is empty, the array is zero, where it has content,
> it is  >0.  When items are added to the plot (points, lines, bars, or
> labels), the corresponding positions in PlotMask are incremented by an
> amount that can vary for different kinds of items (for example, right
> now Bars don't increment as much as points or lines).
> The function KPlotWidget::placeLabel() is responsible for positioning
> item labels.  It attempts to place the label close to the point to
> which it belongs, while minimizing the label's overlap with masked
> regions of the plot.  Ideally, it won't overlap with masked regions at
> all.  This is done in a rather brute-force way: it tests label
> positions in a 40x40 grid around the position of the point, and
> determines the "cost" for placing the label at each position.  Higher
> cost is incurred for (a) overlapping with a masked region, (b) being
> further from the point position, and (c) extending beyond the bounds
> of the plot.  The position that has the lowest "cost" is then adopted,
> and the label is drawn at that position.
> You can get an idea of the CPU impact of this cost-analysis using
> the test suite I added to kdeeduplot.  Display the "Points, lines
> and bars" plot, and then resize the window.  Note the smoothness of
> the redraws.  Now display "Points, lines and bars with labels" and
> resize the window.  The redraws take much longer in this case.
> CCMAIL: kde-edu at kde.org
>  M  +33 -27    kplotobject.cpp
>  M  +154 -5    kplotwidget.cpp
>  M  +64 -0     kplotwidget.h
>  M  +8 -12     tests/testplot_widget.cpp
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