Enhancing performance drawing polygons with many holes
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I'm drawing complex polygons with many vertices and holes.
Code sample:QImage image; // some image QPainter painter; painter.begin(&image); // overall region QPolygon polygon; polygon.setPoints(polyCounts, (int*)polyPoints); QRegion region(polygon); // cutting holes while ( holesCount-- > 0 ) { QPolygon subtractedPolygon; subtractedPolygon.setPoints(holePointsCount, (int*)holePoints); QRegion subtractedRegion(subtractedPolygon); region = region.subtract(subtractedRegion); // defining next hole properties... } // setting clip region painter.setClipRegion(region, Qt::IntersectClip); // painting painter.fillRect( image.size(), Qt::red );It seems to be that main performance leaks are caused by copying points into QPolygon.
I've tried using composition mode QPainter::CompositionMode_SourceOut: it works really faster, but I can't use it because I have to save original image contents.
In Windows API PolyPolygon function seems to be useful in this situation:
https://msdn.microsoft.com/en-us/library/windows/desktop/dd162818(v=vs.85).aspx
Is there any way in Qt to improve performance in this case? -
Hi
would it possible to setup the QPolygon and QRegion outside of
paint so it didnt have to recreate it over and over for each paint? -
Hi
I use different points every rendering so it doesn't prevent from adding new points into QPolygon every painting operation.
