RVTK Example: Input/Output.

The result of example described in previous sections looks like:
example2

The routine to get png (or any other image format) is to use one special case of a filters - exporters. They have input but no output except file one. To get the hardcopy we should first run a filter which convert the content of rendering window into vtkImageData and then put this data into image file.

vtkWindowToImageFilter()->f
    f$SetInput(.vtk)
    f$Modified()

vtkPNGWriter()->png
    png$SetFileName("example2.png")
    png$SetInput(f$GetOutput())
    png$Write()

The result is not much different from the result we would get by taking a screenshot of rendering window (ImageMagick would do this job OK). To get scalable output in vector format (ps or pdf) the special case of exporter should be used - GL2PS one. The corresponding code is not built by default in VTK so to enable it you first have to take special care to check it in ccmake while configuring VTK and then install RVTK.GL2PS R-package.

library(RVTK.GL2PS)
vtkGL2PSExporter()->gp
gp$SetInput(.vtk)
gp$SetSortToBSP()
gp$SetFileFormatToPDF()
gp$SetFilePrefix("example2")
gp$Write()

SetSortToBSP() method enables more careful calculation of intersections which leads to better image quality. The format of output (as well as result file extension) is controlled by methods SetFileFormatToPDF()/SetFileFormatToPS().SetFilePrefix() - is the name of the result file without extension. If you look into result file you will understand why GL2PS considered alpha. Although for simple models it is applicable very well but for more complicated one it fails due to drawbacks of postscript language (it was not designed for 3D rendering). In our example the opacity information is not handled by converter.