Usage with Freetype, wrong values returned

[Jorn Vernee]

Hey Alessandro,

I think there is a bug in this section of your code:

         // Let's now iterate over the structs and print the encoding 
(which is problematic)
         MemorySegment arrPointer = FT_FaceRec.charmaps$get(faceMemory);
         arrPointer.get(POINTER, 0)
             .reinterpret(FT_CharMapRec_.$LAYOUT().byteSize() * num)
             .elements(FT_CharMapRec_.$LAYOUT())
             .forEach(Test::printCharMap);

Looking at the documentation: [1], [2]. The 'charmaps' field of a face 
is an array of _pointers_ to FT_CharMapRec_ (note that FT_CharMap is a 
pointer to a FT_CharMapRec_), not an array of FT_CharMapRec_. Your code, 
however, is getting the pointer to the first struct from the array, and 
then reinterpreting that pointer as an array of structs, while it's 
actually just a pointer to a single FT_CharMapRec_ struct (not an 
array). That explains why the first element looks valid, but the second 
doesn't.

Treating the array as an array of pointers instead, I think this should 
work:

         // Let's now iterate over the structs and print the encoding 
(which is problematic)
         MemorySegment arrPointer = FT_FaceRec.charmaps$get(faceMemory);
         arrPointer
             .reinterpret(POINTER.byteSize() * num) // it's an array of 
pointers
             .elements(POINTER) // the elements are pointers
             .map(s -> s.get(POINTER, 0)) // 's' is a slice of the 
array. Get a pointer to a struct from the array
             .forEach(Test::printCharMap);

HTH,
Jorn

[1]: 
https://freetype.org/freetype2/docs/reference/ft2-face_creation.html#ft_facerec
[2]: 
https://freetype.org/freetype2/docs/reference/ft2-character_mapping.html#ft_charmap

On 13/11/2023 11:11, Alessandro Parisi wrote:
> Hello everyone,
> In the recent weeks, I've been experimenting with Project Panama on 
> JDK 21. I'm trying to create a wrapper for the Freetype font library 
> written in C, but I'm having some issues, probably because I still 
> don't understand very well the FFM API.
> While using the code generated by JExtract, I noticed that it fails to 
> parse the /charmaps/ array from the FT_FaceRec 
> <https://freetype.org/freetype2/docs/reference/ft2-face_creation.html#ft_facerec> struct. 
> With the TTF font, I'm testing, there are two /charmaps/, the values 
> of the first one are the same printed by the native code too, but for 
> the second, the values are completely randomic
> Here is a little reproducer: FreetypeMRE 
> <https://www.dropbox.com/scl/fi/gitugnyxe3kyomm4m0pke/FreetypeMRE.zip?rlkey=tvnrsb5ernwasmxj6cgrjyqqq&dl=0>
> Running the Test class will print the two /charmaps/. There is also a 
> little .exe I built to check the output of native code, it's located 
> in the src/native directory (there is also the C src code)
> Am I doing something wrong, or is this a bug?
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