CODEWITHSUNDEEP
c#bitmapc++-cligdi+
Ace_Radom
Ace_Radom

Reputation: 31

Convert a C# Bitmap to a native C++ Bitmap under GDI+

I created a Bitmap like following in C# (for example):

Image image = Image.FromFile("xxx.png");
Bitmap bitmap = new(image.Width, image.Height, PixelFormat.Format32bppArgb);
Graphics graphics = Graphics.FromImage(bitmap);
graphics.DrawImage(image, 0, 0, image.Width, image.Height);

And now I need to pass this Bitmap to C++ and I meet problems.

I tried to write a convert function like:

Gdiplus::Bitmap* Utils::BitmapConverter::Convert(Drawing::Bitmap^ managedBitmap)
{
    IntPtr hBitmap = managedBitmap->GetHbitmap();
    return Gdiplus::Bitmap::FromHBITMAP((HBITMAP)hBitmap.ToPointer(), NULL);
}

But it doesn't work perfectly: something like alpha channel is lost.

What should I actually change in my convert function?

Upvotes: 1

Views: 53

Answers (1)

Rony M.
Rony M.

Reputation: 405

Make sure the Bitmap is created with PixelFormat.Format32bppArgb (which supports the alpha channel). Try using GetHbitmap(Color::Transparent) to keep the alpha channel when making the HBITMAP (don't forget to delete the HBITMAP handle to prevent memory leaks).

Also, depending on how you pass the Bitmap from C# to C++ (like via PInvoke or COM), you might need extra steps to transfer the bitmap correctly. That is, assuming you already have the interop method set up.

Upvotes: 0

Related Questions