Data Transfer Between Managed and Unmanaged Memory Space

Exchanging data between .Net application and WiT Engine requires the transfer of data between managed and unmanaged memory space. To do this, you need to use Marshal class static methods.

C# code may differ from Visual Basic because unsafe code is allowed in C#. This is an advantage of C#.

The following sample code demonstrates how you can get pixel values of an image (width×height unsigned 8-bit) produced by WiT Engine to your .Net application. In the callback method, the rawData argument is an unmanaged pointer. 

[C#]
using System.Runtime.InteropServices;

unsafe
{
    byte *p = (byte *)(void *)rawData;
    byte value;
    for (int i = 0; i < width * height; i++, p++) value = *p;
}

[Visual Basic]
Imports System.Runtime.InteropServices

Dim size As Integer = width * height
Dim val(size) As Byte
Marshal.Copy(rawData, val, 0, size)
Dim pixVal As Byte
For i = 0 To size - 1 Step 1
    pixVal = val(i)
Next

The following sample code demonstrates how you can transfer pixel values of an image (width×height unsigned 8-bit) from your .Net application. to WiT Engine, using the SetInputData method. Notice that the memory allocated by Marshal.AllocHGlobal must be explicitly released by Marshal.FreeHGlobal. 

[C#]
unsafe
{
    byte * data = (byte *)Marshal.AllocHGlobal(width * height);
    for (int i = 0; i < width; ++i)
        for (int j = 0; j < height; ++j)
            data[i*width + j] = (byte)j;
    string header = String.Format("OBJ_B H CorImage CorUByte {0} {1}", 
        width, height);
    WiT.engine.SetInputData(name, header, header.Length, (IntPtr)data, 
        width * height);
    Marshal.FreeHGlobal((IntPtr)data);
}

[Visual Basic]
Dim size As Integer = width * height
Dim data As IntPtr = Marshal.AllocHGlobal(size)
Dim i As Integer
Dim j As Integer
Dim pos As Integer = 0
Dim val(size) As Byte
For i = 0 To width - 1 Step 1
    For j = 0 To height - 1 Step 1
        val(pos) = CType(j, Byte)
        pos += 1
    Next
Next
Marshal.Copy(val, 0, data, size)
Dim header As String = String.Format("OBJ_B H CorImage CorUByte {0} {1}",_
    width, height)
WiT.engine.SetInputData(name, header, header.Length, CType(data, IntPtr),_
    size)
Marshal.FreeHGlobal(CType(data, IntPtr))

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