Changing size of background canvas makes ugly PNGs

[chaosphere2112]

Ran into this issue while working on #1113; what happens is this:

import vcs, cdms2, sys, os
cfile = cdms2.open(os.path.join(sys.prefix, "sample_data", "clt.nc"))
x = vcs.init()
x.plot(cfile["clt"], bg=1)
x.png("orig.png")
x.bgX = 1000
x.bgY = 750
x.update()
x.png("resize.png")

and you get these outputs:

orig.png

resize.png

This looks to be an issue with VTK's handling of resizing a background window, not something we're doing:

import vtk

win = vtk.vtkRenderWindow()
win.SetSize(300, 300)

ren = vtk.vtkRenderer()
ren.SetBackground(.5, .4, .3)

win.AddRenderer(ren)
win.SetOffScreenRendering(True)

filter = vtk.vtkWindowToImageFilter()
filter.SetInput(win)
filter.Update()

writer = vtk.vtkPNGWriter()
writer.SetInputConnection(filter.GetOutputPort())
writer.SetFileName("base.png")
writer.Write()

win.SetSize(600, 300)
filter = vtk.vtkWindowToImageFilter()
filter.SetInput(win)
filter.Update()

writer.SetInputConnection(filter.GetOutputPort())
writer.SetFileName("resized.png")
writer.Write()

base.png

resized.png

If you do the same but with OffScreenRendering False, you get the expected images.

@aashish24 @doutriaux1 This is the source of my only outstanding concerns on #1113. I've got fixes that make the animation behave "correctly" but trigger this bug, but I'd say that the way it behaves currently (where it will always render the animation at the original resolution of the render window) is less bad than this bug.

[chaosphere2112]

Filed bug on the VTK bugtracker for this issue. @aashish24 @dlonie

[aashish24]

Thanks. We will have a look at it. The test code is really useful.

• Aashish