vb.net camera pinvoke error - vb.net

Question

This question may have been asked before but im just starting out with VB.Net and was given this application to fix that uses the webcam of the pc/ tablet but I cant figure out the pinvoke error
here is my code:
Imports System.IO
Public Class frm
CaptureWebCam
Const CAP As Short = &H400S
Const CAP_DRIVER_CONNECT As Integer = CAP + 10
Const CAP_DRIVER_DISCONNECT As Integer = CAP + 11
Const CAP_EDIT_COPY As Integer = CAP + 30
Const CAP_SET_PREVIEW As Integer = CAP + 50
Const CAP_SET_PREVIEWRATE As Integer = CAP + 52
Const CAP_SET_SCALE As Integer = CAP + 53
Const WS_CHILD As Integer = &H40000000
Const WS_VISIBLE As Integer = &H10000000
Const SWP_NOMOVE As Short = &H2S
Const SWP_NOSIZE As Short = 1
Const SWP_NOZORDER As Short = &H4S
Const HWND_BOTTOM As Short = 1
Dim iDevice As Integer = 0 ' Normal device ID
Dim hHwnd As Integer ' Handle value to preview window
Public image_base64String As String
' Declare function from AVI capture DLL.
Declare Auto Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Object) As Integer
Declare Auto Function SetWindowPos Lib "user32" Alias "SetWindowPos" (ByVal hwnd As Integer, ByVal hWndInsertAfter As Integer, ByVal x As Integer, ByVal y As Integer, ByVal cx As Integer, ByVal cy As Integer, ByVal wFlags As Integer) As Integer
Declare Auto Function DestroyWindow Lib "user32" (ByVal hndw As Integer) As Boolean
Declare Auto Function capCreateCaptureWindowA Lib "avicap32.dll" (ByVal lpszWindowName As String, ByVal dwStyle As Integer, ByVal x As Integer, ByVal y As Integer, ByVal nWidth As Integer, ByVal nHeight As Short, ByVal hWndParent As Integer, ByVal nID As Integer) As Integer
Private Sub OpenForm()
Dim iHeight As Integer = picCapture.Height
Dim iWidth As Integer = picCapture.Width
' Open Preview window in picturebox .
' Create a child window with capCreateCaptureWindowA so you can display it in a picturebox.
hHwnd = capCreateCaptureWindowA(iDevice, WS_VISIBLE Or WS_CHILD, 0, 0, 600, 480, picCapture.Handle, IntPtr.Zero)
' Connect to device
If SendMessage(hHwnd, CAP_DRIVER_CONNECT, iDevice, IntPtr.Zero) Then
' Set the preview scale
SendMessage(hHwnd, CAP_SET_SCALE, True, IntPtr.Zero)
' Set the preview rate in milliseconds
SendMessage(hHwnd, CAP_SET_PREVIEWRATE, 66, IntPtr.Zero)
' Start previewing the image from the camera
SendMessage(hHwnd, CAP_SET_PREVIEW, True, IntPtr.Zero)
' Resize window to fit in picturebox
SetWindowPos(hHwnd, HWND_BOTTOM, 0, 0, picCapture.Width, picCapture.Height, SWP_NOMOVE Or SWP_NOZORDER)
Else
' Error connecting to device close window
DestroyWindow(hHwnd)
End If
End Sub
Private Function btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCapture.Click
Dim data As IDataObject
Dim bmap As Image
' Copy image to clipboard
SendMessage(hHwnd, CAP_EDIT_COPY, 0, 0)
' Get image from clipboard and convert it to a bitmap
data = Clipboard.GetDataObject()
If data.GetDataPresent(GetType(System.Drawing.Bitmap)) Then
bmap = CType(data.GetData(GetType(System.Drawing.Bitmap)), Image)
picCapture.Image = bmap
Dim saveFileDialog1 As New SaveFileDialog()
saveFileDialog1.Filter = "Jpeg Image|*.jpg|Bitmap Image|*.bmp|Gif Image|*.gif"
saveFileDialog1.Title = "Save an Image File"
saveFileDialog1.FileName = "Image001"
If saveFileDialog1.ShowDialog() = Windows.Forms.DialogResult.OK Then
' If the file name is not an empty string open it for saving.
If saveFileDialog1.FileName <> "" Then
' Saves the Image via a FileStream created by the OpenFile method.
Dim fs As System.IO.FileStream = CType(saveFileDialog1.OpenFile(), System.IO.FileStream)
picCapture.Image.Save(fs, System.Drawing.Imaging.ImageFormat.Jpeg)
fs.Close()
End If
End If
End If
End Function
Public Function getImage() As String
Dim bmap As Image
Dim ms As New MemoryStream
bmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg)
Dim bytes() As Byte = ms.ToArray
' Dim image_base64String As String = Convert.ToBase64String(bytes)
image_base64String = Convert.ToBase64String(bytes)
'MsgBox(image_base64String)
Return image_base64String
End Function
Private Sub frmcap_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Leave
' Disconnect from device
SendMessage(hHwnd, CAP_DRIVER_DISCONNECT, iDevice, 0)
' close window
DestroyWindow(hHwnd)
End Sub
Private Sub frmCaptureWebCam_Load(sender As Object, e As EventArgs) Handles MyBase.Load
OpenForm()
End Sub
End Class
you will notice that I'm also trying to return the image via the image_base64 variable
Can someone help me with the code as I get the following error:
PInvokeStackImbalance was detected
Message: A call to PInvoke function
'GCOS3_Mobile_Host_Application!GCOS3_Mobile_Host_Application.frmCaptureWebCam::SendMessage'
has unbalanced the stack. This is likely because the managed PInvoke
signature does not match the unmanaged target signature. Check that
the calling convention and parameters of the PInvoke signature match
the target unmanaged signature.

Answer 1

SendMessage declaration according to pinvoke should be like this
Declare Auto Function SendMessage Lib "user32.dll" (ByVal hWnd As IntPtr, ByVal msg As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
Also see the tips for Overloads there.
In your code you have declared lParam, which provides additional message-specific information, as object.
And you are passing IntPtr.Zero, so I think using ByVal lParam As IntPtr will be more specific.

Answer 2

I used the emgu library and got it to return the base 64 string:
Imports Emgu.CV
Imports Emgu.CV.Util
Imports System.IO
Public Class frmEmguCapture
Private imagecapture As Capture
Private imageCaptureReady As Boolean = False
Public b64 As String
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles tmrUpdateImage.Tick
tmrUpdateImage.Enabled = False
If imageCaptureReady Then
pbWebCamStream.Visible = True
lblConnecting.Visible = False
btnCapture.Enabled = True
pbWebCamStream.Image = imagecapture.QueryFrame.Bitmap
tmrUpdateImage.Enabled = True
Else
MessageBox.Show("Error connecting to camera.", "Error conecting to camera.", MessageBoxButtons.OK, MessageBoxIcon.Error)
Me.Close()
End If
End Sub
Public Function btnCapture_Click(sender As Object, e As EventArgs) Handles btnCapture.Click
tmrUpdateImage.Enabled = False
pbWebCamStream.Visible = True
lblConnecting.Visible = False
btnCapture.Enabled = True
pbWebCamStream.Image = imagecapture.QueryFrame.Bitmap
Dim bmap As Image
bmap = imagecapture.QueryFrame.Bitmap
Dim ms As New MemoryStream
bmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg)
Dim bytes() As Byte = ms.ToArray
Dim image_base64String As String = Convert.ToBase64String(bytes)
image_base64String = Convert.ToBase64String(bytes)
b64 = image_base64String
imagecapture.Dispose()
Me.Close()
'MsgBox(image_base64String)
Return image_base64String
End Function
Private Sub frmEmguCapture_Load(sender As Object, e As EventArgs) Handles MyBase.Load
tmrLoad.Enabled = True
End Sub
Private Sub tmrLoad_Tick(sender As Object, e As EventArgs) Handles tmrLoad.Tick
tmrLoad.Enabled = False
Try
imagecapture = New Capture
imageCaptureReady = True
tmrUpdateImage.Enabled = True
Catch ex As Exception
MessageBox.Show("Error connecting to camera.", "Error conecting to camera.", MessageBoxButtons.OK, MessageBoxIcon.Error)
Me.Close()
End Try
End Sub
End Class