Binding Help

[gudenau]

I am working on adding a binding to LWJGL3 that could be useful for development of games.

I have been converting the header file to the Kotlan stuff based on the GLFW files, so far I don't have errors and I think I understand the structure of the enums and defines, my current problem is that when I test built it to check the Java output my binding was not in the release.

What did I do wrong? I added my files in templates/src/main/kotlin/org/lwjgl/library/libraryTypes.kt and templates/src/main/kotlin/org/lwjgl/library/templates/library.kt.

(also to the mods, sorry for making a couple posts so close. Figured these where different enough to warrant that)

[gudenau]

I've managed to get it to build to a degree by adding the library to /config/build-bindings.xml, looks like I probably need to add it to the other platform ones as well.

[spasi]

Hey gudenau,

See this commit of the recently added rpmalloc bindings as an example. These are the non-obvious places where changes need to happen:

- /build.xml
- /build.gradle (missing in the above commit, added with this one)
- /config/build-bindings.xml
- /config/linux/build.xml
- /config/macos/build.xml
- /config/windows/build.xml
- /modules/generator/src/main/kotlin/org/lwjgl/generator/Generator.kt

[gudenau]

Hey gudenau,

See this commit of the recently added rpmalloc bindings as an example. These are the non-obvious places where changes need to happen:

- /build.xml
- /build.gradle (missing in the above commit, added with this one)
- /config/build-bindings.xml
- /config/linux/build.xml
- /config/macos/build.xml
- /config/windows/build.xml
- /modules/generator/src/main/kotlin/org/lwjgl/generator/Generator.kt

I found those using grep, any way this could be streamlined any more?

[spasi]

any way this could be streamlined any more?

It's probably going to be simpler/cleaner when we port the Ant build to Gradle/Kotlin.

[gudenau]

Now I have another issue, there is a recursive definition in a header.

Basically this:
C:

struct structure;

typedef void (*callbackMethod)(struct structure *data);

struct structure{
    callbackMethod callback;
}

Kotlin:

var structure = struct(
    LIBRARY_PACKAGE,
    "structure"
){
    callback.member("callback", "")
}

var callback = "callback".callback(
    LIBRARY_PACKAGE, void,
    "callback", "",
    structure.p.IN("data", "")
)

How do I resolve this? It says to define types explicitly and I am not sure what that means, I know nothing about Kotlin.

[spasi]

This happens often with structs that are defined in a linked-list manner. To break the recursion, you define a struct type without a body. Everything should be in the same order as the C definitions:

var structure_p = struct(LIBRARY_PACKAGE, "structure").p // declare the struct type (as a pointer to a yet undefined struct)

var callback = "callback".callback(
    LIBRARY_PACKAGE, void,
    "callback", "",

    structure_p.IN("data", "")
)

var structure = struct(LIBRARY_PACKAGE, "structure") { // define the struct type
    callback.member("callback", "")
}

[gudenau]

This happens often with structs that are defined in a linked-list manner. To break the recursion, you define a struct type without a body. Everything should be in the same order as the C definitions:

var structure_p = struct(LIBRARY_PACKAGE, "structure").p // declare the struct type (as a pointer to a yet undefined struct)

var callback = "callback".callback(
    LIBRARY_PACKAGE, void,
    "callback", "",

    structure_p.IN("data", "")
)

var structure = struct(LIBRARY_PACKAGE, "structure") { // define the struct type
    callback.member("callback", "")
}

Thanks!

Sorry for being such an idiot with this stuff. :-/

[spasi]

Sorry for being such an idiot with this stuff. :-/

It's OK, the template DSL is anything but friendly. It's the reason very few people have been able to make binding contributions.

[gudenau]

Next issue that I have not found a fix for:

There is a function that has a return type of struct strucutre**`, a null terminated array of structs. How can I make this work when the library allocates the memory for this? NullTerminated and PointerArray do not seem to work for this.

[spasi]

There is a function that has a return type of struct strucutre**`, a null terminated array of structs

That sounds odd. Isn't there an output parameter that returns the array size? Could you post more details about the function? (i.e. signature and documentation)

[gudenau]

There is a function that has a return type of struct strucutre**`, a null terminated array of structs

That sounds odd. Isn't there an output parameter that returns the array size? Could you post more details about the function? (i.e. signature and documentation)

I agree, it is quite odd as it goes. There is a free method that you need to call though, at least you can clean it up.

Definition in the headers:

const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(libusb_context *ctx);

Then the documentation for the function:

const struct libusb_pollfd** libusb_get_pollfds   (   libusb_context *    ctx   )   
Retrieve a list of file descriptors that should be polled by your main loop as libusb event sources.

The returned list is NULL-terminated and should be freed with libusb_free_pollfds() when done. The actual list contents must not be touched.

As file descriptors are a Unix-specific concept, this function is not available on Windows and will always return NULL.

Parameters
ctx   the context to operate on, or NULL for the default context
Returns
a NULL-terminated list of libusb_pollfd structures
NULL on error
NULL on platforms where the functionality is not available

[spasi]

You could try something like this:

// replace struct libusb_pollfd** with an opaque pointer
const..opaque_p(
    "get_pollfds",
    "",

    libusb_context.p.IN("ctx", "")
)

// example usage:
LibUSBPollFD fd;
for (long pp = libusb_get_pollfds(ctx); (fd = LibUSBPollFD.create(memGetAddress(pp))) != null; pp += POINTER_SIZE) {
    // ...use file descriptor...
}

If this style occurs again, I'll try to add NullTerminated support to return values. The above would become:

PointerBuffer pp = libusb_get_pollfds(ctx);
for (int i = 0; i < pp.remaining(); i++) {
    LibUSBPollFD fd = LibUSBPollFD.create(pp.get(i));
    // ...use file descriptor...
}

[gudenau]

Nice, I made it generate source files that break the java compiler with comments ending early. :-P

[gudenau]

I presume I should use an opaque pointer for the structs that have no body in the headers?