Converting IntPtr (CPU buffer representing Y channel) to AndroidJavaObject without copy

When calling `AcquireCameraImageBytes` to retrieve an `CameraImageBytes` instance and the underlying `Y` IntPtr buffer, I need to pass that IntPtr to my own AAR library which takes a `ByteBuffer` as argument. I could not find a way of converting the `IntPtr` to an `AndroidJavaObject` reference which would allow me to pass it to my method.

Code (CSharp):

1. using (GoogleARCore.CameraImageBytes image = GoogleARCore.Frame.CameraImage.AcquireCameraImageBytes())
2. {
3.     if (!image.IsAvailable)
4.     {
5.         return;
6.     }
7.  
8.     int width = image.Width;
9.     int height = image.Height;
10.     IntPtr yPixelBuffer = image.Y;
11.  
12.     using (AndroidJavaClass utilsClass = new AndroidJavaClass("com.mypackage.MyClassUtils"))
13.     {
14.         utilsClass.CallStatic("setCurrentBuffer", yPixelBuffer, width, height); // <-- Need to pass a AndroidJavaObject here but no way to just pass the ByteBuffer
15.     }
16. }

the Java method implementation:

Code (CSharp):

1. public class MyClassUtils {
2.     public static final void setCurrentBuffer(
3.                                               ByteBuffer buffer,
4.                                               int width,
5.                                               int height) {
6. }

Is there any way to convert the `IntPtr` to its underlying `ByteBuffer` reference ?

 

The IntPtr is actually backed by a C unsigned char*, i.e. a raw pointer to the Y channel. The most efficient way to do this would be to jump through JNI (in C) and create a ByteBuffer using the JNI NewDirectByteBuffer.

Alternatively, you can always use Marshal.Copy to convert an IntPtr into a C# byte[], and then do normal Unity things to convert that to Java objects. That involves a bunch of copies of the image which may impact performance, though.

 

The IntPtr is actually backed by a C unsigned char* @chaosemer thanks a lot for this, I really thought it was pointing to the address of a ByteBuffer object, my bad. I don't want to create a new ByteBuffer with NewDirectByteBuffer but to directly pass the IntPtr to my .so C++ library and use the pointer to unsigned char* there. I reckon I will have to do that. Thanks again.