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Add Qwt drawPolyline() performance workaround

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This commit is contained in:
Allan Bazinet 2024-12-02 09:44:36 -08:00
parent 30e06660cb
commit 65794ebdb5
1 changed files with 19 additions and 2 deletions
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21
plotter.cpp
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@ -26,6 +26,12 @@ namespace
constexpr qreal RDP_EPSILON = 2.0;
// The Qt Raster engine seems to have terrible performance when
// drawing large polylines; the size at which we should split
// drawing into smaller lines.
constexpr qsizetype POLYLINE_SIZE = 6;
// Resize debounce interval, in milliseconds; adjust to taste.
constexpr auto RESIZE_DEBOUNCE_INTERVAL = 100;
@ -454,11 +460,22 @@ CPlotter::drawData(WF::SWide swide)
}
// Draw the spectrum line, reducing the resulting points prior to
// drawing them, but keeping the collection capacity.
// drawing them, but keeping the collection capacity. We also work
// around what seems to be a performance bug in all versions of Qt
// up to and including 6.8, when drawing large polylines; this was
// culled from the Qwt library's workaround for the issue. Doubles
// overall program performance, pretty much.
m_points.erase(rdp(m_points), m_points.end());
p.setRenderHint(QPainter::Antialiasing);
p.drawPolyline(m_points);
for (qsizetype i = 0;
i < m_points.size();
i += POLYLINE_SIZE)
{
p.drawPolyline(m_points.data() + i, qMin(POLYLINE_SIZE + 1,
m_points.size() - i));
}
}
// Save the data against a potential replot requirement.