drawing of colorbar in vcs too slow

[doutriaux1]

the following code, takes around .5sec just to draw the colorbar.

import cdms2,sys,vcs
x=vcs.init()
f=cdms2.open(sys.prefix+"/sample_data/clt.nc")
s=f("clt")
x.plot(s)

The code to draw the colorbar should be rewritten in pure VTK.
current code:
https://github.com/UV-CDAT/uvcdat/blob/master/Packages/vcs/Lib/template.py#L1369

in the vtkbackend we call it at:
https://github.com/UV-CDAT/uvcdat/blob/master/Packages/vcs/Lib/VTKPlots.py#L1127

I think we should update
vtkScalarBarActor

[doutriaux1]

@dlonie let me know if that's not clear

[doutriaux1]

@dlonie also let's use the same branch for this, I'm using: https://github.com/UV-CDAT/uvcdat/tree/optimize_vtk

[alliepiper]

I'll take a look soon.

[alliepiper]

You're on the right track. Adding a vtkScalarBarActor that uses the same vtkLookupTable as the data mapper should be sufficient. Let me know how I can help.

[doutriaux1]

@dlonie no the vtkscalarbaractor won't work. I tried it. If I remember correctly you can't control very well the viewport (i.e dims) and you can't control the text on it. You can't add extension arrows. Also we need to be able to control the text fonts color height etc... that is why I assigned it to kit ware because it will need a serious overall of the scalarbaractor.

[alliepiper]

Ah, you want a different style. It's probably best to write a new one from scratch if you need that level of control over the elements. If we go this route, can you provide a list of the specific features/customizations you need?

Alternatively, have you profiled the current scalar bar drawing code? If we can figure out what's making it take so long, we might be able to optimize it and keep the existing look and feel without too much effort.

[doutriaux1]

yes there's many places where the current code can be optimized. python loops over the 255 colors is bad while creating the fillarea object, then while processing the fillarea object we go thru that loop again. We already have the lookupup table in VTKPlot.py so I think using ScalarBarActor (a new one) is the way to go. There's not so much more that needs to be added, I almost think the current one is close form functional for us. A short sumary of what our colorbar actor would need
1- ability to add extensions arrows
2- ability to control the thickness/stretch
3- ability to control which values are effectively written as text (can't write 255 vals obviously)
4- ability to map these vlue to specific strings
5- ability to control the textactor (colro/font/size/orientation etc...) of the actual text rendered.

[alliepiper]

See the branch I just pushed. I profiled the existing implementation and found some quick optimizations. Allocating and rendering separate polydata, mappers, and actors for each vertical slice of the colorbar eats up a lot of time (you really want to try to minimize the number of actors in VTK for best performance), and the data fits quite well into a single multicell polydata.

This is roughly 3x faster on my machine and produces the same results. Would this improve performance enough for you folks? IMO, if we can avoid spending a week or two developing a new C++ scalar bar, we should ;-)