The other post in this site is Simple VB.Net Wrapper for Ghostscript Dll. It doesn't work for me too.
First, the source code goes to InOutErrCallBack method in this part:
gsapi_init_with_args(InstanceHndl, NumArgs + 1, Args)
When this occurr, the execution freeze. After this occurs, the next calls to RunGS method returns false in this part:
If gsapi_new_instance(InstanceHndl, IntPtr.Zero) <> 0 Then
Return False
Exit Function
End If
The return value of gsapi_new_instance is -100:
Ghostscript API - Return codes
The gswin32.dll is in C:\Windows\System32 and BIN project folder.
I wrote other wrapper too, and occur something similar:
Option Explicit On
Imports System.Runtime.InteropServices
'''
''' https://msdn.microsoft.com/en-us/library/aa719104(v=vs.71).aspx
''' http://www.codeproject.com/Articles/32274/How-To-Convert-PDF-to-Image-Using-Ghostscript-API
''' http://www.ghostscript.com/doc/current/API.htm
''' https://stackguides.com/questions/16929383/simple-vb-net-wrapper-for-ghostscript-dll
'''
Public Class GhostscriptDLLWrapper
#Region "GhostScript Import"
<StructLayout(LayoutKind.Sequential)> _
Public Structure GSVersion
Public product As IntPtr
Public copyright As IntPtr
Public revision As Integer
Public revisionDate As Integer
End Structure
'''
''' <summary>This function returns the revision numbers and strings of the Ghostscript interpreter library;
''' you should call it before any other interpreter library functions to make sure that the
''' correct version of the Ghostscript interpreter has been loaded.</summary>
'''
<DllImport("gsdll32.dll", CharSet:=CharSet.Ansi, EntryPoint:="gsapi_revision")> _
Public Shared Function GsapiRevision(ByRef pVer As GSVersion, ByVal pSize As Integer) As Integer
End Function
''' <summary>Create a new instance of Ghostscript.</summary>
''' <param name="pinstance"></param>
''' <param name="caller_handle"></param>
''' <returns>The instance passed to other GS function</returns>
<DllImport("gsdll32.dll", CharSet:=CharSet.Ansi, EntryPoint:="gsapi_new_instance")> _
Public Shared Function GsapiNewInstance( _
ByRef instance As IntPtr, _
ByVal caller_handle As IntPtr) As Integer
End Function
''' <summary>This will make the conversion</summary>
''' <param name="instance"></param><param name="argc"></param>
''' <param name="argv"></param>
''' <returns>0 if is ok</returns>
<DllImport("gsdll32.dll", CharSet:=CharSet.Ansi, EntryPoint:="gsapi_init_with_args")> _
Public Shared Function GsapiInitWithArgs( _
ByVal instance As IntPtr, _
ByVal argc As Integer, _
<MarshalAs(UnmanagedType.LPArray, ArraySubType:=UnmanagedType.LPStr)> _
ByVal argv() As String) As Integer
End Function
''' <summary>Exit the interpreter</summary>
''' <param name="instance"></param>
''' <returns></returns>
<DllImport("gsdll32.dll", CharSet:=CharSet.Ansi, EntryPoint:="gsapi_exit")> _
Public Shared Function GsapiExit(ByVal instance As IntPtr) As Integer
End Function
''' <summary>Destroy an instance of Ghostscript.</summary>
''' <param name="instance"></param>
<DllImport("gsdll32.dll", CharSet:=CharSet.Ansi, EntryPoint:="gsapi_delete_instance")> _
Public Shared Function GsapiDeleteInstance(ByVal instance As IntPtr)
End Function
#End Region
End Class
I call these methods in this way:
'https://stackguides.com/questions/16929383/simple-vb-net-wrapper-for-ghostscript-dll
'Shift arguments to begin at index 1 (Ghostscript requirement)
'Initialise the interpreter. This calls gs_main_init_with_args() in imainarg.c. See below for return codes.
'The arguments are the same as the "C" main function: argv[0] is ignored and the user supplied arguments are argv[1] to argv[argc-1].
Dim argsCount As Integer = args.Length
ReDim Preserve args(argsCount)
System.Array.Copy(args, 0, args, 1, argsCount)
SyncLock SyncRoot
Dim gsInstance As IntPtr
Dim result As Integer
result = GhostscriptDLLWrapper.GsapiNewInstance(gsInstance, IntPtr.Zero)
If (result = 0) Then
Try
result = GhostscriptDLLWrapper.GsapiInitWithArgs( _
gsInstance, _
args.Length, _
args _
)
If (result < 0) Then
Throw New InvalidOperationException("Erro ao converter páginas do PDF em imagens PNG")
End If
If File.Exists(outputImgPath) Then
objFileStream = New FileStream(outputImgPath, FileMode.Open)
Dim length As Int32 = objFileStream.Length
Dim bytes(length) As Byte
objFileStream.Read(bytes, 0, length)
objFileStream.Close()
objMemoryStream = New MemoryStream(bytes, False)
objImages.Add(Image.FromStream(objMemoryStream))
Else
Throw New InvalidOperationException("Erro ao converter páginas do PDF em imagens PNG")
End If
Catch ex As Exception
Throw New InvalidOperationException("Erro ao converter páginas do PDF em imagens PNG", ex)
End Try
End If
GhostscriptDLLWrapper.GsapiExit(gsInstance)
GhostscriptDLLWrapper.GsapiDeleteInstance(gsInstance)
End SyncLock
My parameter sequence:
Dim outputImgPath As String
outputImgPath = "C:\Download\DocumentosV2\Protocolo\Pronunciamento\" + Guid.NewGuid.ToString("N") + ".png"
Dim args() As String = { _
"-dNOPAUSE", _
"-dBATCH", _
"-dSAFER", _
"-dQUIET", _
"-sDEVICE=png16m", _
String.Format("-r{0}", resolucao), _
"-dTextAlphaBits=2", _
"-dGraphicsAlphaBits=2", _
String.Format("-dFirstPage={0}", pageNumber), _
String.Format("-dLastPage={0}", pageNumber), _
String.Format("-sOutputFile={0}", outputImgPath), _
"-f", _
pdfPath _
}
