Clarification C++ export

[mkaratha]

I'm trying to Pinvoke the C++ dll to .NET and appreciate support regarding definition of CPaths64 .

From the header export it says:

//This 'counter path' has a single x,y coord pair with 'y' (not 'x')
// containing the number of paths that follow. ('x' = 0).
// _______________________________
// |counter|path1|path2|...|pathN|
// |addr0 |addr1|addr2|...|addrN| (*addr0[0]=0; *addr0[1]=N)
// _______________________________

Is the 'counter path' 2x4 bytes (=8 bytes) or 2x8 bytes (64-bit system)?

Thanks
Michael

[AngusJohnson]

Is the 'counter path' 2x4 bytes (=8 bytes) or 2x8 bytes (64-bit system)?

The counter pseudo-path always contains one (x,y) vertex, where x and y are both 64bit integers.
The x value should always be 0 and the y value indicates the number of paths contained (ignoring the counter 'path').

Edit:
And I'm seriously considering redesigning clipper.export.h.

Edit2:
Done! 😁

[mkaratha]

Many thanks, and I finally figured it out after your comments.
Coming from the .NET-world, things are really different.

If this helps other:
The CPaths64 pointer starts with a 8-bytes pointer (Which actually is an address to 16-bytes 'counter path', (8-bytes value=0 + 8 bytes value=N). The following bytes in the CPaths64 pointer (starting at byte position 8 with 8 bytes lengths) represent each 'path' pointer.

[mkaratha]

Agree with your consideration of redesigning CPaths64. It would be more consistent to use the first pair (2x8 bytes) as a counter and identifier.

The difference in .NET would be using Marshal.ReadInt64 alone or in combination with Marshal.ReadIntPtr

[JimBobSquarePants]

Sorry to butt in but why use PInvoke when there is .NET version? Is the performance difference really that much?

[AngusJohnson]

Yes, the performance difference could well justify using the C++ compiled DLL.

[AngusJohnson]

I've just uploaded to the repository a major redesign of clipper.export.h where path and polytree structures are now exposed as either int64 or double arrays.

[AngusJohnson]

And I've attached a sample C# application that compares using the native C# compiled code vs using the new C++ compiled code in the DLL. The time differences are quite significant even in this relatively simple example. And when clipping becomes more complex (eg by increasing the edge count in the attached sample), the time differences become even more significant.
CSharp_TestApp2.zip

[mkaratha]

I REALLY like the new way to call the exported functions. Passing arrays instead of pointers makes disposing MUCH easier in .NET environment. Many thanks and keep up the great work!