How To Convert PDF to Image Using Ghostscript API

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Collections;

namespace ConvertPDF
{
    /// <summary>
    /// Class to convert a pdf to an image using GhostScript DLL
    /// Credit for this code go to:Rangel Avulso
    /// i only fix a little bug and refactor a little
    /// http://www.hrangel.com.br/index.php/2006/12/04/converter-pdf-para-imagem-jpeg-em-c/
    /// </summary>
    /// <seealso cref="http://www.hrangel.com.br/index.php/2006/12/04/converter-pdf-para-imagem-jpeg-em-c/"/>
    class PDFConvert
    {
        #region GhostScript Import

        /// <summary>Create a new instance of Ghostscript. This instance is passed to most other gsapi functions. The caller_handle will be provided to callback functions.
        ///  At this stage, Ghostscript supports only one instance. </summary>
        /// <param name="pinstance"></param>
        /// <param name="caller_handle"></param>
        /// <returns></returns>
        [DllImport("gsdll32.dll", EntryPoint="gsapi_new_instance")]
        private static extern int gsapi_new_instance (out IntPtr pinstance, IntPtr caller_handle);

        /// <summary>This is the important function that will perform the conversion</summary>
        /// <param name="instance"></param>
        /// <param name="argc"></param>
        /// <param name="argv"></param>
        /// <returns></returns>
        [DllImport("gsdll32.dll", EntryPoint="gsapi_init_with_args")]
        private static extern int gsapi_init_with_args (IntPtr instance, int argc, IntPtr argv);
        /// <summary>
        /// Exit the interpreter. This must be called on shutdown if gsapi_init_with_args() has been called, and just before gsapi_delete_instance(). 
        /// </summary>
        /// <param name="instance"></param>
        /// <returns></returns>
        [DllImport("gsdll32.dll", EntryPoint="gsapi_exit")]
        private static extern int gsapi_exit (IntPtr instance);

        /// <summary>
        /// Destroy an instance of Ghostscript. Before you call this, Ghostscript must have finished. If Ghostscript has been initialised, you must call gsapi_exit before gsapi_delete_instance. 
        /// </summary>
        /// <param name="instance"></param>
        [DllImport("gsdll32.dll", EntryPoint="gsapi_delete_instance")]
        private static extern void gsapi_delete_instance (IntPtr instance);

        #endregion

        #region Variables
        private string _sDeviceFormat;

        private int _iWidth;
        private int _iHeight;
        private int _iResolutionX;
        private int _iResolutionY;
        private int _iJPEGQuality;

        private Boolean _bFitPage;

        private IntPtr _objHandle;
        #endregion
        #region Proprieties
        public string OutputFormat
        {
            get { return _sDeviceFormat; }
            set { _sDeviceFormat = value; }
        }

        public int Width
        {
            get { return _iWidth; }
            set { _iWidth = value; }
        }

        public int Height
        {
            get { return _iHeight; }
            set { _iHeight = value; }
        }

        public int ResolutionX
        {
            get { return _iResolutionX; }
            set { _iResolutionX = value; }
        }

        public int ResolutionY
        {
            get { return _iResolutionY; }
            set { _iResolutionY = value; }
        }

        public Boolean FitPage
        {
            get { return _bFitPage; }
            set { _bFitPage = value; }
        }
        /// <summary>Quality of compression of JPG</summary>
        public int JPEGQuality
        {
            get { return _iJPEGQuality; }
            set { _iJPEGQuality = value; }
        }
        #endregion
        #region Init
        public PDFConvert(IntPtr objHandle)
        {
            _objHandle = objHandle;
        }

        public PDFConvert()
        {
            _objHandle = IntPtr.Zero;
        }
        #endregion
        private byte[] StringToAnsiZ(string str)
        {
            //' Convert a Unicode string to a null terminated Ansi string for Ghostscript.
            //' The result is stored in a byte array. Later you will need to convert
            //' this byte array to a pointer with GCHandle.Alloc(XXXX, GCHandleType.Pinned)
            //' and GSHandle.AddrOfPinnedObject()
            int intElementCount;
            int intCounter;
            byte[] aAnsi;
            byte bChar;

            intElementCount = str.Length;
            aAnsi = new byte[intElementCount+1];
            for(intCounter = 0; intCounter < intElementCount;intCounter++)
            {
                bChar = (byte)str[intCounter];
                aAnsi[intCounter] = bChar;
            }

            aAnsi[intElementCount] = 0;
            return aAnsi;
        }

        /// <summary>Convert the file!</summary>
        public void Convert(string inputFile,string outputFile)
        {
            //Avoid to work when the file doesn't exist
            if (!System.IO.File.Exists(inputFile))
            {
                System.Windows.Forms.MessageBox.Show(string.Format("The file :'{0}' doesn't exist",inputFile));
                return;
            }

            int intReturn;
            IntPtr intGSInstanceHandle;
            object[] aAnsiArgs;
            IntPtr[] aPtrArgs;
            GCHandle[] aGCHandle;
            int intCounter;
            int intElementCount;
            IntPtr callerHandle;
            GCHandle gchandleArgs;
            IntPtr intptrArgs;

            string[] sArgs = GetGeneratedArgs(inputFile,outputFile);

            // Convert the Unicode strings to null terminated ANSI byte arrays
            // then get pointers to the byte arrays.
            intElementCount = sArgs.Length;
            aAnsiArgs = new object[intElementCount];
            aPtrArgs = new IntPtr[intElementCount];
            aGCHandle = new GCHandle[intElementCount];

            for(intCounter = 0; intCounter< intElementCount; intCounter++)
            {
                aAnsiArgs[intCounter] = StringToAnsiZ(sArgs[intCounter]);
                aGCHandle[intCounter] = GCHandle.Alloc(aAnsiArgs[intCounter], GCHandleType.Pinned);
                aPtrArgs[intCounter] = aGCHandle[intCounter].AddrOfPinnedObject();
            }
            gchandleArgs = GCHandle.Alloc(aPtrArgs, GCHandleType.Pinned);
            intptrArgs = gchandleArgs.AddrOfPinnedObject();

            intReturn = gsapi_new_instance(out intGSInstanceHandle, _objHandle);
            callerHandle = IntPtr.Zero;
            try
            {
                intReturn = gsapi_init_with_args(intGSInstanceHandle, intElementCount, intptrArgs);
            }
            catch (Exception ex)
            {
                System.Windows.Forms.MessageBox.Show(ex.Message);
            }
            finally
            {
                for (intCounter = 0; intCounter < intReturn; intCounter++)
                {
                    aGCHandle[intCounter].Free();
                }
                gchandleArgs.Free();
                gsapi_exit(intGSInstanceHandle);
                gsapi_delete_instance(intGSInstanceHandle);
            }

        }

        private string[] GetGeneratedArgs(string inputFile, string outputFile)
        {
            // Count how many extra args are need - HRangel - 11/29/2006, 3:13:43 PM
            ArrayList lstExtraArgs = new ArrayList();

            if ( _sDeviceFormat=="jpg" && _iJPEGQuality > 0 && _iJPEGQuality < 101)
                lstExtraArgs.Add("-dJPEGQ=" + _iJPEGQuality);

            if (_iWidth > 0 && _iHeight > 0)
                lstExtraArgs.Add("-g" + _iWidth + "x" + _iHeight);

            if (_bFitPage)
                lstExtraArgs.Add("-dPDFFitPage");

            if (_iResolutionX > 0)
            {
                if (_iResolutionY > 0)
                    lstExtraArgs.Add("-r" + _iResolutionX + "x" + _iResolutionY);
                else
                    lstExtraArgs.Add("-r" + _iResolutionX);
            }
            // Load Fixed Args - HRangel - 11/29/2006, 3:34:02 PM
            int iFixedCount = 7;
            int iExtraArgsCount = lstExtraArgs.Count;
            string[] args = new string[iFixedCount + lstExtraArgs.Count];
            args[0]="pdf2img";//this parameter have little real use
            args[1]="-dNOPAUSE";//I don't want interruptions
            args[2]="-dBATCH";//stop after
            args[3]="-dSAFER";
            args[4]="-sDEVICE="+_sDeviceFormat;//what kind of export format i should provide
            //For a complete list watch here:
            //http://pages.cs.wisc.edu/~ghost/doc/cvs/Devices.htm
            //Fill the remaining parameters
            for (int i=0; i < iExtraArgsCount; i++)
            {
                args[5+i] = (string) lstExtraArgs[i];
            }
            //Fill outputfile and inputfile
            args[5 + iExtraArgsCount] = string.Format("-sOutputFile={0}",outputFile);
            args[6 + iExtraArgsCount] = string.Format("{0}",inputFile);
            return args;
        }
    }
}