[vtkusers] drawing very quickly in an overlay (tracking mouse with a line)

[Malcolm Drummond]

Hi

Can anyone offer advice on drawing very quickly in an overlay?

I have a companion '2D' window which basically renders a 3D parallel projection that has been transformed by the camera matrix from the main '3D' window. In the second window the user creates fence polygons around regions of interest with a mouse - after which I do point-in-polygon stuff etc. So far so good - however on large datasets the rendering of the polygon segment lags way behind the mouse position.

I draw the most recent segment of the fence polygon (ie. the one that is tracking the mouse) in an overlay layer in the hope that I could use backing store on the background renderer, but I'm not seeing any real difference in performance. Maybe I'm not using backing store correctly - I switch backing store on when I start catching mouse events for the polygons, switch off when I have the whole polygon, but all the rendering in-between seems to be refreshing both renderers.

Has anyone experience with this?  

Thanks
Malcolm Drummond
GeoVision cc
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