Append datasets and props to Viewer scene

[banesullivan]

I'm trying to make a plotter class based on the itkwidgets.Viewer class and I need ways to append datasets and their properties to the scene.

import pyvista as pv
from pyvista import examples

from itkwidgets import view, Viewer

class PlotterITK():
    def __init__(self, **kwargs):
        self.plotter = Viewer()
        
    def add_mesh(self, mesh, color=None, scalars=None, clim=None,
                 opacity=1.0, n_colors=256, cmap='viridis',
                 **kwargs):
        """Adds mesh to the scene"""
        if not pv.is_pyvista_obj(mesh):
            mesh = pv.wrap(mesh)
        if not isinstance(mesh, pv.PolyData):
            mesh = mesh.extract_geometry()
        
        if self.plotter.geometries is None:
            self.plotter.geometries = [mesh,]
#             if color:
#                 # how do I set the color????? this doesn't work
#                 self.plotter.geometry_colors = [np.array(pv.parse_color(color)).reshape(-1, 3),]
        else:
            self.plotter.geometries = self.plotter.geometries.append(mesh)
#             if color:
#                 self.plotter.geometry_colors = self.plotter.geometry_colors.append(pv.parse_color(color))

        if scalars is not None:
            mesh.active_scalars = scalars
        
        return
        
    def show(self, **kwargs):
        """Show in cell output"""
        return self.plotter
    
mesh = examples.download_st_helens().warp_by_scalar()

# sample usage
plotter = PlotterITK()
plotter.add_mesh(mesh.wireframe(), scalars='Elevation') # pass args for coloring too
plotter.add_mesh(mesh.contour(), color='k') # pass args for coloring too
plotter.show()

This doesn't really work though... @thewtex proposed a solution in #154 (comment) but I cannot get any of this to work because self.plotter.geometries.append(mesh) returns None.

Can we implement a feature to append datasets and their display properties (color/colormap, style, etc.) on the fly?

[banesullivan]

One workaround is to keep track of all the meshes and their display properties and pass them all to the itkwidgets.view function at once during the PlotterITK.show() call but this isn't ideal for me

[thewtex]

One workaround is to keep track of all the meshes and their display properties and pass them all to the itkwidgets.view function at once during the PlotterITK.show()

A variant of this, at least until #166 is addressed, is a good approach to avoid rendering-related computation before .show(). .show() does the rendering. self.plotter.geometries = self.geometries, etc. could be called in .show()`.

[banesullivan]

Whoops, sorry for duplicating #166