I am trying without success to write code in C# to pass a bitmap to an unmanaged c++ DLL and return a POINT structure.
I have done a lot of research on the internet, but have not found the "Gotcha" article or piece of code to help me resolve my issue.
The best I have been able to come up with so far is an unmanaged c++ DLL, wrapped with a managed c++ dll, called by my C# app. In testing that, I can pass simple types, such as an integer and return an integer with no problem. Now for the issue I am having, the bitmap.
I have tried passing an HBITMAP (using the GetHBitmap() function of my bitmap in c#), but I get errors during compile of "cannot convert parameter 1 from 'System::IntPtr' to 'HBITMAP'" and "Class1.FindImage(void *, void *) is inaccessible due to it's protection level".
Here is some of my code:
Main App:
class Program
{
[StructLayout(LayoutKind.Sequential)]
public struct POINT
{
public int X;
public int Y;
public POINT(int x, int y)
{
this.X = x;
this.Y = y;
}
public static implicit operator System.Drawing.Point(POINT p)
{
return new System.Drawing.Point(p.X, p.Y);
}
public static implicit operator POINT(System.Drawing.Point p)
{
return new POINT(p.X, p.Y);
}
}
static void Main(string[] args)
{
Image src = Image.FromFile("Pin.png");
Image tgt = Image.FromFile("screen.png");
Bitmap bsrc = new Bitmap(src);
Bitmap btgt = new Bitmap(tgt);
IntPtr bs = bsrc.GetHbitmap();
IntPtr bt = btgt.GetHbitmap();
POINT p = Class1.FindImage(bs, bt);
}
}
ImportWrap.h:
namespace ImportWrap {
public ref class Class1
{
public:
static POINT FindImage(IntPtr source, IntPtr target);
};
}
ImportWrap.cpp:
static POINT FindImage(IntPtr source, IntPtr target)
{
return ImgFuncs::MyImgFuncs::FindImage(source, target);
}
ImgFuncs.h
typedef long LONG;
typedef void *PVOID;
typedef PVOID HANDLE;
typedef HANDLE HBITMAP;
typedef struct tagPOINT {
LONG x;
LONG y;
} POINT, *PPOINT;
namespace ImgFuncs
{
class MyImgFuncs
{
public:
static __declspec(dllexport) POINT FindImage(HBITMAP source, HBITMAP target);
};
}
ImgFuncs.cpp
namespace ImgFuncs
{
POINT MyImgFuncs::FindImage(HBITMAP source, HBITMAP target)
{
POINT p;
p.x = 1;
p.y = 2;
return p;
}
}
What am I doing wrong, or am I going completely off the map with my approach? I would GLADLY entertain any suggestions regarding the correct way to code what I am trying to do. I have some C++ code that is used to find an image within another image that works quite fast. Unfortunately, even using lockbits in c#, it's not fast enough. So I would like to make use of the c++ code for the image search.
I am sure I will run into further snags, but might be able to handle it if I can get past this stumbling block. As you can see, my C++ knowledge is limited.
You cannot use native struct types as a return value, C# can't handle them. Casting from IntPtr to HBITMAP requires a double cast. Like this:
Add an assembly reference to System.Drawing. You might then also want to consider passing a Bitmap^ instead of an IntPtr to make it even easier to use.