# Frustum

VTKExamples/CSharp/GeometricObjects/Frustum

### Description

This example gets the frustum from a camera and displays it on the screen.
A tutorial on how to setup a Windows Forms Application utilizing ActiViz.NET can be found here: Setup a Windows Forms Application to use ActiViz.NET

### Code

Frustum.cs

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Windows.Forms;
    using System.Diagnostics;

    using Kitware.VTK;

    namespace ActiViz.Examples {
       public partial class Form1 : Form {
          public Form1() {
             InitializeComponent();
          }

          private void renderWindowControl1_Load(object sender, EventArgs e) {
             try {
                Frustum();
             }
             catch(Exception ex) {
                MessageBox.Show(ex.Message, "Exception", MessageBoxButtons.OK);
             }
          }

          private void Frustum() {
             // Create a frustum.
             // in this example we need the renderer first to retrieve the active camera
             // in order to get camera's frustum planes
             vtkRenderWindow renderWindow = renderWindowControl1.RenderWindow;
             vtkRenderer renderer = renderWindow.GetRenderers().GetFirstRenderer();
             vtkCamera camera = renderer.GetActiveCamera();
             double[] aspect = renderer.GetAspect();
             double aspectRatio = aspect[0] / aspect[1];

             // allocate memory for 24 unmanaged doubles
             int size = Marshal.SizeOf(typeof(double)) * 24;
             IntPtr ptr = Marshal.AllocHGlobal(size);
             camera.GetFrustumPlanes(aspectRatio, ptr);
             // in case we would need this values directly we could copy
             // the unmanaged double array to a managed array like so:

             // double[] planesArray = new double[24];
             // Marshal.Copy(ptr, planesArray, 0, 24);

             // but fortunately we can forward the IntPtr directly to the function
             // SetFrustumPlanes()
             vtkPlanes planes = vtkPlanes.New();
             planes.SetFrustumPlanes(ptr);
             // free unmanaged memory
             Marshal.FreeHGlobal(ptr);

             vtkFrustumSource frustumSource = vtkFrustumSource.New();
             frustumSource.SetPlanes(planes);
             frustumSource.Update();

             vtkPolyData frustum = frustumSource.GetOutput();
             // Visualize
             vtkPolyDataMapper mapper = vtkPolyDataMapper.New();
             mapper.SetInput(frustum);
             vtkActor actor = vtkActor.New();
             actor.SetMapper(mapper);

             renderer.SetBackground(.2, .1, .3); // Background color dark purple
             renderer.AddActor(actor);
             renderer.ResetCamera();
          }
       }
    }