#!/usr/bin/env python

# In this example vtkClipPolyData is used to cut a polygonal model
# of a cow in half. In addition, the open clip is closed by triangulating
# the resulting complex polygons.

import vtk
from vtk.util.misc import vtkGetDataRoot
from vtk.util.colors import peacock, tomato
VTK_DATA_ROOT = vtkGetDataRoot()

# First start by reading a cow model. We also generate surface normals for
# prettier rendering.
cow = vtk.vtkBYUReader()
cow.SetGeometryFileName(VTK_DATA_ROOT + "/Data/Viewpoint/cow.g")
cowNormals = vtk.vtkPolyDataNormals()
cowNormals.SetInput(cow.GetOutput())

# We clip with an implicit function. Here we use a plane positioned near
# the center of the cow model and oriented at an arbitrary angle.
plane = vtk.vtkPlane()
plane.SetOrigin(0.25, 0, 0)
plane.SetNormal(-1, -1, 0)

# vtkClipPolyData requires an implicit function to define what it is to
# clip with. Any implicit function, including complex boolean combinations
# can be used. Notice that we can specify the value of the implicit function
# with the SetValue method.
clipper = vtk.vtkClipPolyData()
clipper.SetInput(cowNormals.GetOutput())
clipper.SetClipFunction(plane)
clipper.GenerateClipScalarsOn()
clipper.GenerateClippedOutputOn()
clipper.SetValue(0.5)
clipMapper = vtk.vtkPolyDataMapper()
clipMapper.SetInput(clipper.GetOutput())
clipMapper.ScalarVisibilityOff()
backProp = vtk.vtkProperty()
backProp.SetDiffuseColor(tomato)
clipActor = vtk.vtkActor()
clipActor.SetMapper(clipMapper)
clipActor.GetProperty().SetColor(peacock)
clipActor.SetBackfaceProperty(backProp)

# Here we are cutting the cow. Cutting creates lines where the cut
# function intersects the model. (Clipping removes a portion of the
# model but the dimension of the data does not change.)
#
# The reason we are cutting is to generate a closed polygon at the
# boundary of the clipping process. The cutter generates line
# segments, the stripper then puts them together into polylines. We
# then pull a trick and define polygons using the closed line
# segements that the stripper created.
cutEdges = vtk.vtkCutter()
cutEdges.SetInput(cowNormals.GetOutput())
cutEdges.SetCutFunction(plane)
cutEdges.GenerateCutScalarsOn()
cutEdges.SetValue(0, 0.5)
cutStrips = vtk.vtkStripper()
cutStrips.SetInput(cutEdges.GetOutput())
cutStrips.Update()
cutPoly = vtk.vtkPolyData()
cutPoly.SetPoints(cutStrips.GetOutput().GetPoints())
cutPoly.SetPolys(cutStrips.GetOutput().GetLines())

# Triangle filter is robust enough to ignore the duplicate point at
# the beginning and end of the polygons and triangulate them.
cutTriangles = vtk.vtkTriangleFilter()
cutTriangles.SetInput(cutPoly)
cutMapper = vtk.vtkPolyDataMapper()
cutMapper.SetInput(cutPoly)
cutMapper.SetInput(cutTriangles.GetOutput())
cutActor = vtk.vtkActor()
cutActor.SetMapper(cutMapper)
cutActor.GetProperty().SetColor(peacock)

# The clipped part of the cow is rendered wireframe.
restMapper = vtk.vtkPolyDataMapper()
restMapper.SetInput(clipper.GetClippedOutput())
restMapper.ScalarVisibilityOff()
restActor = vtk.vtkActor()
restActor.SetMapper(restMapper)
restActor.GetProperty().SetRepresentationToWireframe()

# Create graphics stuff
ren = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)

# Add the actors to the renderer, set the background and size
ren.AddActor(clipActor)
ren.AddActor(cutActor)
ren.AddActor(restActor)
ren.SetBackground(1, 1, 1)
ren.ResetCamera()
ren.GetActiveCamera().Azimuth(30)
ren.GetActiveCamera().Elevation(30)
ren.GetActiveCamera().Dolly(1.5)
ren.ResetCameraClippingRange()

renWin.SetSize(300, 300)
iren.Initialize()

# Lets you move the cut plane back and forth by invoking the function
# Cut with the appropriate plane value (essentially a distance from
# the original plane).  This is not used in this code but should give
# you an idea of how to define a function to do this.
def Cut(v):
    clipper.SetValue(v)
    cutEdges.SetValue(0, v)
    cutStrips.Update()
    cutPoly.SetPoints(cutStrips.GetOutput().GetPoints())
    cutPoly.SetPolys(cutStrips.GetOutput().GetLines())
    cutMapper.Update()
    renWin.Render()
 
renWin.Render()
iren.Start()
