How to: Display and Select Meshes

[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

You can create and display an array of meshes so that when a mesh is picked (tapped) on the device, it changes color.

Note Note

Managed Direct3D mobile applications require Windows Mobile version 5.0 software for Pocket PCs and Smartphones. See External Resources for the .NET Compact Framework for information about Windows Mobile software and SDKs.

The form for this code example has the following objects:

  • A Mesh object for the active mesh.

  • An array of nine Mesh objects of various colors that can be picked.

  • A Vector3 structure that defines the mesh locations.

  • Two Vector3 structures that define the bounding box.

  • A Device object.

The form's constructor specifies settings for the device's PresentationParameters property, creates the Device object, adds the OnDeviceReset event handler to the device's DeviceReset event, and then calls the OnDeviceReset method to begin creating the meshes. The following table describes the methods that render the meshes and enable user interaction.

Method

Actions

OnDeviceReset

Creates the meshes, places them at locations in the bounding box, and defines the transformation matrices.

OnPaint

Begins the scene, draws the meshes, and ends the scene.

OnMouseDown

Demonstrates picking a mesh by using a technique that creates a ray through the logical 3-D space and performs a box-ray intersection.

The ray represents pressing the stylus through the 3-D space. The box represents a bounding box around the 3-D object. If the two intersect, the user has clicked on a location that contains the 3-D object.

The following code example provides a complete form. It displays Mesh objects of various colors that can be picked. When a mesh is picked, its color changes.


Imports System
Imports System.Drawing
Imports System.Windows.Forms
Imports Microsoft.WindowsMobile.DirectX
Imports Microsoft.WindowsMobile.DirectX.Direct3D
Imports Microsoft.VisualBasic




Class MeshPickingHowto
    Inherits Form
    Private Const numberOfMeshes As Integer = 9
    Private meshes() As Mesh
    Private meshColors() As Color = {Color.Green, Color.Orange, Color.Purple, Color.Pink, Color.Violet, Color.Blue, Color.Yellow, Color.Brown, Color.Aquamarine}

    Private meshLocations() As Vector3
    Private meshBoundingBoxMinValues() As Vector3
    Private meshBoundingBoxMaxValues() As Vector3
    Private activeMesh As Mesh

    Private device As Device


    Public Sub New() 
        Dim present As PresentParameters

        Me.Text = "Mesh Picking"

        ' Enable the form to be closed.
        ' This is required so that Hwnd of the form changes.
        Me.MinimizeBox = False

        present = New PresentParameters()
        present.Windowed = True
        present.AutoDepthStencilFormat = DepthFormat.D16
        present.EnableAutoDepthStencil = True
        present.SwapEffect = SwapEffect.Discard

        device = New Device(0, DeviceType.Default, Me, CreateFlags.None, present)
        AddHandler device.DeviceReset, AddressOf OnDeviceReset
        OnDeviceReset(Nothing, EventArgs.Empty)

    End Sub


    Private Sub OnDeviceReset(ByVal sender As Object, ByVal e As EventArgs) 
        ' Meshes must be recreated whenever the device
        ' is reset, no matter which pool they are created in.
        meshes = New Mesh(numberOfMeshes) {}
        meshLocations = New Vector3(numberOfMeshes) {}
        meshBoundingBoxMinValues = New Vector3(numberOfMeshes) {}
        meshBoundingBoxMaxValues = New Vector3(numberOfMeshes) {}
        activeMesh = Nothing

        ' Create several meshes and associated data.
        Dim i As Integer
        For i = 0 To numberOfMeshes
            Dim vertexData As GraphicsStream

            meshes(i) = Mesh.Box(device, 1F, 1F, 1F)

            ' Arrange the boxes in a grid, with each
            ' successive box farther in the distance.
            meshLocations(i) = New Vector3((i Mod 3) * 2 - 2, i / 3 * 2 - 2, i)

            ' Compute the bounding box for a mesh.
            Dim description As VertexBufferDescription = meshes(i).VertexBuffer.Description
            vertexData = meshes(i).VertexBuffer.Lock(0, 0, LockFlags.ReadOnly)
            Geometry.ComputeBoundingBox(vertexData, meshes(i).NumberVertices, description.VertexFormat, meshBoundingBoxMinValues(i), meshBoundingBoxMaxValues(i))
            meshes(i).VertexBuffer.Unlock()
        Next i
        ' Set the transformation matrices.
        device.Transform.Projection = Matrix.PerspectiveFovRH(System.Convert.ToSingle(Math.PI) / 4F, System.Convert.ToSingle(Me.ClientSize.Width) / System.Convert.ToSingle(Me.ClientSize.Height), 0.001F, 40)

        device.Transform.View = Matrix.LookAtRH(New Vector3(0, 2, - 7), New Vector3(0, 0, 0), New Vector3(0, 1, 0))

        device.RenderState.Ambient = Color.White

    End Sub


    Protected Overrides Sub OnPaintBackground(ByVal e As PaintEventArgs) 
        ' Do nothing.
    End Sub

    Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs) 
        Dim material As New Material()

        ' Begin the scene and clear the back buffer to black.
        device.BeginScene()
        device.Clear(ClearFlags.Target Or ClearFlags.ZBuffer, Color.Black, 1F, 0)

        ' Draw each mesh to the screen.
        ' The active mesh is drawn in red.
        Dim i As Integer
        For i = 0 To numberOfMeshes
            If activeMesh Is meshes(i) Then
                material.Ambient = Color.Red
            Else
                material.Ambient = meshColors(i)
            End If
            device.Transform.World = Matrix.Translation(meshLocations(i))
            device.Material = material
            meshes(i).DrawSubset(0)
        Next i

        ' Finish the scene and present it on the screen.
        device.EndScene()
        device.Present()

    End Sub


    ' This method demonstrates picking.
    Protected Overrides Sub OnMouseDown(ByVal e As MouseEventArgs) 
        ' The technique used here is to create a ray through the entire
        ' logical 3-D space, and then perform an intersection test
        ' for the bounding box and ray.
        Dim i As Integer
        For i = 0 To numberOfMeshes
            Dim nearVector As New Vector3(e.X, e.Y, 0)
            Dim farVector As New Vector3(e.X, e.Y, 1)

            ' Create ray.
            nearVector.Unproject(device.Viewport, device.Transform.Projection, device.Transform.View, Matrix.Translation(meshLocations(i)))

            farVector.Unproject(device.Viewport, device.Transform.Projection, device.Transform.View, Matrix.Translation(meshLocations(i)))

            farVector.Subtract(nearVector)

            ' Perform intersection test for the bounding box and ray.
            If Geometry.BoxBoundProbe(meshBoundingBoxMinValues(i), meshBoundingBoxMaxValues(i), nearVector, farVector) Then
                ' Perform operation on detection of click on mesh object.
                ' In this case, you designate the mesh as the active
                ' mesh and invalidate the window so that it is redrawn.
                activeMesh = meshes(i)
                Me.Invalidate()
                Exit For
            End If
        Next i

    End Sub


    Shared Sub Main() 
        Application.Run(New MeshPickingHowto())

    End Sub
End Class


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