Question

I am trying to implement an application which uses RIOT (Radical Image Optimization Tool) for batch image optimizaton. I can successfully import riot.dll into my app. But I cannot figure out how to pass a Windows DIB (Device Independent Bitmap) handle to RIOT function.

Here is my code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace Riot_Test
{
    public partial class Form1 : Form
    {

        [DllImport("RIOT.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
        static extern bool RIOT_LoadFromDIB(IntPtr hDIB, IntPtr hwndParent, [MarshalAs(UnmanagedType.LPStr)] string fileName = "", [MarshalAs(UnmanagedType.LPStr)] string iniFile = "", int flags = 0, [MarshalAs(UnmanagedType.LPStr)] string buf = "");

        [DllImport("RIOT.dll")]
        static extern void RIOT_Show();

        [DllImport("RIOT.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
        static extern bool RIOT_LoadFromFile([MarshalAs(UnmanagedType.LPStr)] string filename, int flags = 0);

        [DllImport("RIOT.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto, SetLastError = true)]
        static extern bool RIOT_SaveToFile(IntPtr hDIB, IntPtr hwndParent, [MarshalAs(UnmanagedType.LPStr)] string fileName, [MarshalAs(UnmanagedType.LPStr)] string origFilename = "", ulong byteSize = 0, [MarshalAs(UnmanagedType.LPStr)]  string errorText = "", int flags = 0, [MarshalAs(UnmanagedType.LPStr)] string buf = "");

        public Form1()
        {
            InitializeComponent();
            //RIOT_Show();
            IntPtr hdib = IntPtr.Zero;
            IntPtr hwnd = IntPtr.Zero;
            string errorText = "";

            Bitmap bmp = new Bitmap("dene.jpg");
            hdib = bmp.GetHbitmap();


            string fn = "optim2.jpg";
            string fno = "dene.jpg";
            bool result = RIOT_SaveToFile_U(hdib, hwnd, fn);


        }
    }
}

RIOT_Show() and RIOT_Load_From_File() are working as expected but when I try to call RIOT_SaveToFile() it gives me this error:

System.AccessViolationException was unhandled – Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

So my questions are:

1. How can I convert a System.Bitmap object to Windows DIB handle ?
2. If I can’t convert is it possible to use a C++ library (if there is) to do the job for me and return the DIB handle?

Edit:

I’ve changed my code to this but it gives the same error.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace from_vb
{
    public partial class Form1 : Form
    {
        [DllImport("gdi32.dll", SetLastError = true)]
        static extern IntPtr CreateCompatibleDC(IntPtr hdc);

        [DllImport("gdi32.dll", ExactSpelling = true, PreserveSig = true, SetLastError = true)]
        static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);

        [DllImport("gdi32.dll")]
        static extern int GetObject(IntPtr hgdiobj, int cbBuffer, IntPtr lpvObject);

        [DllImport("gdi32.dll")]
        static extern IntPtr CreateDIBSection(IntPtr hdc, [In] ref GDI32BITMAPINFOHEADER pbmi, uint pila, out IntPtr ppvBits, IntPtr hSection, uint dwOffset);

        [DllImport("gdi32.dll")]
        static extern int GetDIBits(IntPtr hdc, IntPtr hbmp, uint uStartScan,
           uint cScanLines, [Out] byte[] lpvBits, ref GDI32BITMAPINFOHEADER lpbmi, uint uUsage);

        [DllImport("gdi32.dll")]
        static extern bool DeleteObject(IntPtr hObject);

        [DllImport("gdi32.dll")]
        static extern bool DeleteDC(IntPtr hdc);

        [DllImport("gdi32.dll")]
        static extern bool GdiFlush();

        [DllImport("RIOT.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto, SetLastError = true)]
        static extern bool RIOT_SaveToFile(IntPtr hDIB, IntPtr hwndParent, [MarshalAs(UnmanagedType.LPStr)] string fileName, [MarshalAs(UnmanagedType.LPStr)] string origFilename = "", ulong byteSize = 0, [MarshalAs(UnmanagedType.LPStr)]  string errorText = "", int flags = 0, [MarshalAs(UnmanagedType.LPStr)] string buf = "");


        public const int BI_RGB = 0;
        public const int DIB_PAL_COLORS = 1;

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct GDI32BITMAP
        {
            public int bmType;
            public int bmWidth;
            public int bmHeight;
            public int bmWidthBytes;
            public short bmPlanes;
            public short bmBitsPixel;
            public int bmBits;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct GDI32BITMAPINFOHEADER
        {
            public int biSize;
            public int biWidth;
            public int biHeight;
            public short biPlanes;
            public short biBitCount;
            public int biCompression;
            public int biSizeImage;
            public int biXPelsPerMeter;
            public int biYPelsPerMeter;
            public uint biClrUsed;
            public uint biClrImportant;

            public void Init()
            {
                biSize = (int)Marshal.SizeOf(this);
            }
        }



        public Form1()
        {
            InitializeComponent();
            IntPtr hdc = IntPtr.Zero;
            IntPtr hSrcBitmap = IntPtr.Zero;
            IntPtr pSrcBitmapInfo = IntPtr.Zero;
            IntPtr hDestDIBitmap = IntPtr.Zero;
            IntPtr hDstOldBitmap = IntPtr.Zero;
            IntPtr pDestDIBits = IntPtr.Zero;
            IntPtr hSection = IntPtr.Zero;
            IntPtr hwnd = IntPtr.Zero;
            IntPtr ccDC = IntPtr.Zero;

            Bitmap dotNetBitmap;
            int XDPI, YDPI;

            GDI32BITMAP srcBitmapInfo = new GDI32BITMAP();
            //ccDC = CreateCompatibleDC(hdc);
            IntPtr hDstMemDC = CreateCompatibleDC(hdc);
            GDI32BITMAPINFOHEADER DestDIBMIH = new GDI32BITMAPINFOHEADER();


            dotNetBitmap = new Bitmap("dene.jpg");
            hSrcBitmap = dotNetBitmap.GetHbitmap();
            pSrcBitmapInfo = Marshal.AllocCoTaskMem(Marshal.SizeOf(srcBitmapInfo));

            GetObject(hSrcBitmap, Marshal.SizeOf(srcBitmapInfo),pSrcBitmapInfo);
            srcBitmapInfo = (GDI32BITMAP)Marshal.PtrToStructure(pSrcBitmapInfo, srcBitmapInfo.GetType());




            if (pSrcBitmapInfo != IntPtr.Zero)
            {

                Marshal.FreeCoTaskMem(pSrcBitmapInfo);
            }

            DestDIBMIH.biSize = Marshal.SizeOf(DestDIBMIH);
            DestDIBMIH.biWidth = srcBitmapInfo.bmWidth;
            DestDIBMIH.biHeight = srcBitmapInfo.bmHeight;
            DestDIBMIH.biPlanes = srcBitmapInfo.bmPlanes;
            DestDIBMIH.biBitCount = 24;
            DestDIBMIH.biCompression = BI_RGB;

            hDestDIBitmap = CreateDIBSection(hDstMemDC, ref DestDIBMIH, 0, out pDestDIBits, hSection, 0);

            string fn = "optim2.jpg";
            string fno = "dene.jpg";
            bool hede = RIOT_SaveToFile(hDestDIBitmap, hwnd, fn);
        }
    }
}

Answer 1

Here is the “documentation” on that method:

bool RIOT_SaveToFile(HANDLE hDIB, HWND hwndParent,const char *fileName,const char *origFilename=”", unsigned long byteSize=0,char *errorText=”",int flags=0, char *buf=”")

Saves the file with the specified parameters.

Parameters:
hDIB – handle to a Windows DIB image in memory
hwndParent – Not Used. Must be NULL.
fileName – full path to the file to be saved (only JPEG is supported)
origFilename – Fill this with the original file name if the DIB is not different than the image from the file
byteSize – filesize of the compressed JPEG image in bytes
errorText – On error errorText is filled with the error message
flags – save flags. See bellow
buf – not used. Leave blank.THe function returns true on success or false on error.If you specify byteSize you can specify any of the save flags, but the quality will not be used.
If you don’t specify byteSize flags are used.
If there are no flags or byteSize is 0 an error is thrown.Flags for RIOT_SaveToFile:0×0001 – keep EXIF
0×0002 – keep IPTC
0×0004 – keep XMP
0×0008 – keep Comments
0×1000 – keep ICC profile0x0800 – save greyscale
0×2000 – save progressive
0×10000 – disable chroma subsamplingAlso you can set a quality flag from 1 to 100Ex: flags=JPEG_SUBSAMPLING_444 | JPEG_PROGRESSIVE | 90
results in a file with no subsampling, progressive with a quality of 90
If you don’t specify quality 75 is used.
You must specify JPEG_PROGRESSIVE if you want progressive.
If you don’t specify JPEG_SUBSAMPLING_444 a default chroma of 4:2:0 is used.

The first issue is with errorText. The doc states, “On error errorText is filled with the error message.” This suggests that you have to pass an array of bytes of un-specified length that will get filled in. That’s hideous.

The second issue is where it says, “If there are no flags or byteSize is 0 an error is thrown.”

My guess is that you’re getting an error and it’s trying to copy bytes into errorText. Try passing a largish byte[] instead of a string.