ngdg's picture

Picking/Selection using Vb.NET

Hello. I've been developing a VB.Net Windows Form Application, learning and using OpenTK from the scratch, with which I'm actually getting by, thanks to your excelent support and documentation.
I started using the GameWindow style, then I moved to GLControl in order to fulfill my needs of an interface. I'm now familiar with the whole drawing thing, including mouse and keyboard inputs, although I'm facing a problem now that I wanted to add a picking support to my application, but I have no clue about how I could do it. I've also been googling and reading this forum, and I've actually found some examples, most of then written in C# and using a certain lib called "Glu" which as far as I'm concerned has been discontinued. My question is: Is there any example (written in VB) from which I could take some ideas? Or is anyone willing to give me some guidelines in order to do it?

Thanks in advance!


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avc81's picture

c# or Vb.NET doesn't matter. just take a look a opentk's picking example (in the example browser) and translate it from c# to

ngdg's picture

Do you mean in the project gallery? I can't seem to find one...

avc81's picture


bhairav's picture

Hi, I checked that example, but it uses color information for picking. Extending the logic for box selection drawn by user may not be all that easy. Can anybody please give a working example of picking using selection?

I googled and tried various solutions proposed, but I think I am going wrong somewhere in the projection matrices.

The code I am using is as follows:

    Public Sub StartPicking(x As Double, y As Double)
        Dim viewport(4) As Integer
        ReDim selectBuffer(128 * 4)
        GL.SelectBuffer(128 * 4, selectBuffer)
        GL.GetInteger(GetPName.Viewport, viewport)
        OpenTK.Graphics.Glu.PickMatrix(x, viewport(3) - y, 4, 4, viewport)
    End Sub
    Public Function GetSelected() As Integer
        Dim SelectedID As Integer
        '---> Render()
        'restoring the original projection matrix
        Dim hits As Integer
        'Returning to normal rendering mode
        hits = GL.RenderMode(RenderingMode.Render)
        Dim closest As UInteger
        closest = UInteger.MaxValue
        Dim Distance As UInteger
        Dim i As Integer
        For i = 0 To hits - 1
            Distance = CUInt(selectBuffer(i * 4 + 1))
            If closest >= Distance Then
                closest = Distance
                selectedId = selectBuffer(i * 4 + 3)
            End If
        Return selectedId
    End Function

I am also allowing rotation by arcball (just in case if it matters). Can anybody please help?