[vtkusers] best way to represent a (planar) irregular polygon ?

[Marie-Gabrielle Vallet]

Hi Brian,
I remember having some problem to render a non-convex polygon. I found an
example, I can't find again where it comes from, and I worked on it. Finally
the following python script does what you want.

You should try to add two filters : a GeometryFilter and a TriangleFilter.
Marie-Gabrielle

 #!/usr/bin/env python

 # This example shows how to visualize polygons, convex or not.

 import vtk

 # Define a set of points - these are the ordered polygon vertices
 polygonPoints = vtk.vtkPoints()
 polygonPoints.SetNumberOfPoints(6)
 polygonPoints.InsertPoint(0, 0, 0, 0)
 polygonPoints.InsertPoint(1,.4,.4, 0)
 polygonPoints.InsertPoint(2, 1, 0, 0)
 polygonPoints.InsertPoint(3, 1, 1, 0)
 polygonPoints.InsertPoint(4,.1,.7, 0)
 polygonPoints.InsertPoint(5, 0, 1, 0)

 # Make a cell with these points
 aPolygon = vtk.vtkPolygon()
 aPolygon.GetPointIds().SetNumberOfIds(6)
 aPolygon.GetPointIds().SetId(0, 0)
 aPolygon.GetPointIds().SetId(1, 1)
 aPolygon.GetPointIds().SetId(2, 2)
 aPolygon.GetPointIds().SetId(3, 3)
 aPolygon.GetPointIds().SetId(4, 4)
 aPolygon.GetPointIds().SetId(5, 5)

 # The cell is put into a mesh (containing only one cell)
 aPolygonGrid = vtk.vtkUnstructuredGrid()
 aPolygonGrid.Allocate(1, 1)
 aPolygonGrid.InsertNextCell(aPolygon.GetCellType(), aPolygon.GetPointIds())
 aPolygonGrid.SetPoints(polygonPoints)

 # This part is needed for non-convex polygon rendering
 aPolygonGeomFilter = vtk.vtkGeometryFilter()
 aPolygonGeomFilter.SetInput(aPolygonGrid)
 aPolygonTriangleFilter = vtk.vtkTriangleFilter()
 aPolygonTriangleFilter.SetInput(aPolygonGeomFilter.GetOutput())
 #
 # This one is only to check the triangulation (when factor < 1)
 aPolygonShrinkFilter = vtk.vtkShrinkFilter()
 aPolygonShrinkFilter.SetShrinkFactor( 0.9 )
 #aPolygonShrinkFilter.SetShrinkFactor( 1.0 )
 aPolygonShrinkFilter.SetInput( aPolygonGrid)

 # Make ready for rendering
 aPolygonMapper = vtk.vtkDataSetMapper()
 aPolygonMapper.SetInput(aPolygonShrinkFilter.GetOutput())
 aPolygonActor = vtk.vtkActor()
 aPolygonActor.SetMapper(aPolygonMapper)
 aPolygonActor.GetProperty().SetDiffuseColor(1, .4, .5)

 # Create the usual rendering stuff.
 ren = vtk.vtkRenderer()
 renWin = vtk.vtkRenderWindow()
 renWin.AddRenderer(ren)
 renWin.SetSize(300, 150)
 iren = vtk.vtkRenderWindowInteractor()
 iren.SetRenderWindow(renWin)

 ren.SetBackground(.1, .2, .4)
 ren.AddActor(aPolygonActor)
 ren.ResetCamera()

 # Render the scene and start interaction.
 iren.Initialize()
 renWin.Render()
 iren.Start()
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