import vtk


# -----------------------------------------------------------------------------
# Points
# -----------------------------------------------------------------------------

points = vtk.vtkPoints()

point_coordinates = [
    # Surface points
    (0.0, 0.0, 0.0),  # 0
    (1.0, 0.0, 0.0),  # 1
    (2.0, 0.0, 0.0),  # 2

    (0.0, 1.0, 0.0),  # 3
    (1.0, 1.0, 0.0),  # 4
    (2.0, 1.0, 0.0),  # 5

    (0.0, 2.0, 0.0),  # 6
    (1.0, 2.0, 0.0),  # 7
    (2.0, 2.0, 0.0),  # 8

    # Separate bar points
    (3.0, 0.0, 0.0),  # 9
    (4.0, 0.0, 0.0),  # 10

    (3.0, 0.6, 0.0),  # 11
    (4.0, 0.6, 0.0),  # 12

    (3.0, 1.2, 0.0),  # 13
    (4.0, 1.2, 0.0),  # 14

    (3.0, 1.8, 0.0),  # 15
    (4.0, 1.8, 0.0),  # 16
]

for p in point_coordinates:
    points.InsertNextPoint(p)


# -----------------------------------------------------------------------------
# Unstructured grid
# -----------------------------------------------------------------------------

mesh = vtk.vtkUnstructuredGrid()
mesh.SetPoints(points)


# -----------------------------------------------------------------------------
# Helper for adding triangles
# -----------------------------------------------------------------------------

def add_triangle(mesh, p0, p1, p2):

    triangle = vtk.vtkTriangle()

    triangle.GetPointIds().SetId(0, p0)
    triangle.GetPointIds().SetId(1, p1)
    triangle.GetPointIds().SetId(2, p2)

    mesh.InsertNextCell(
        triangle.GetCellType(),
        triangle.GetPointIds()
    )


# -----------------------------------------------------------------------------
# Helper for adding lines
# -----------------------------------------------------------------------------

def add_line(mesh, p0, p1):

    line = vtk.vtkLine()

    line.GetPointIds().SetId(0, p0)
    line.GetPointIds().SetId(1, p1)

    mesh.InsertNextCell(
        line.GetCellType(),
        line.GetPointIds()
    )


# -----------------------------------------------------------------------------
# Add 8 triangles
#
#   6 ----- 7 ----- 8
#   | \     | \     |
#   |   \   |   \   |
#   3 ----- 4 ----- 5
#   | \     | \     |
#   |   \   |   \   |
#   0 ----- 1 ----- 2
# -----------------------------------------------------------------------------

add_triangle(mesh, 0, 1, 4)
add_triangle(mesh, 0, 4, 3)

add_triangle(mesh, 1, 2, 5)
add_triangle(mesh, 1, 5, 4)

add_triangle(mesh, 3, 4, 7)
add_triangle(mesh, 3, 7, 6)

add_triangle(mesh, 4, 5, 8)
add_triangle(mesh, 4, 8, 7)


# -----------------------------------------------------------------------------
# Add 4 disconnected lines
#
# Comment these out to test triangles without line elements.
# -----------------------------------------------------------------------------

add_line(mesh, 9, 10)
add_line(mesh, 11, 12)
add_line(mesh, 13, 14)
add_line(mesh, 15, 16)


mesh.Modified()


# -----------------------------------------------------------------------------
# Mapper
#
# Direct:
#
# vtkUnstructuredGrid -> vtkDataSetMapper
#
# No geometry filter.
# -----------------------------------------------------------------------------

mapper = vtk.vtkDataSetMapper()
mapper.SetInputData(mesh)


# -----------------------------------------------------------------------------
# Actor
# -----------------------------------------------------------------------------

actor = vtk.vtkActor()
actor.SetMapper(mapper)

actor.GetProperty().SetRepresentationToSurface()
actor.GetProperty().EdgeVisibilityOn()
actor.GetProperty().SetLineWidth(3.0)


# -----------------------------------------------------------------------------
# Renderer
# -----------------------------------------------------------------------------

renderer = vtk.vtkRenderer()
renderer.AddActor(actor)
renderer.SetBackground(0.15, 0.18, 0.22)


# -----------------------------------------------------------------------------
# Render window
# -----------------------------------------------------------------------------

render_window = vtk.vtkRenderWindow()
render_window.AddRenderer(renderer)
render_window.SetSize(900, 700)


# -----------------------------------------------------------------------------
# Interactor
# -----------------------------------------------------------------------------

interactor = vtk.vtkRenderWindowInteractor()
interactor.SetRenderWindow(render_window)

renderer.ResetCamera()

render_window.Render()
interactor.Start()