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ffi-helper: status

From: Matt Wette
Subject: ffi-helper: status
Date: Fri, 7 Jul 2017 17:18:08 -0700

Hi All,

I am working on a ffi-helper: a program that will read in a C dot-h file and 
generate a Guile dot-scm file which
defines a module to provide hooks into the associated C library.  My goal is to 
have something to release ~Oct 2017.

I have now been able to compile-ffi the following on my Mac. There is some 
non-standard C syntax in sys/cdefs.h
that is driving me crazy, but I have a hack around it (see inc-help below).  
I’m sure there are numerous bugs.

(define-ffi-module (cairo cairo)
  #:pkg-config "cairo"
  #:include '("cairo.h"
  #:inc-help (cond
              ((string-contains %host-type "darwin")
               '(("__builtin" "__builtin_va_list=void*")
                 ("sys/cdefs.h" "__DARWIN_ALIAS(X)=")))
              (else '()))

  ;; the following are bent pipe to scm-module
  #:export (make-cairo-unit-matrix)

(define (make-cairo-unit-matrix)
  (make-cairo_matrix_t #(1.0 0.0 0.0 1.0 0.0 0.0)))

Some of the other Cairo headers (e.g., cairo-ft.h) give me problems with the 
rat’s nest under /usr/include.

However, the above generates 397 FFI declarations into a cairo.scm file which 
is about 6000 lines long.  I’m not 
sure if I want to start testing this code or start converting suggestions and 
have guile-users do some testing.  


P.S.  Here is some sample code from the auto-generated file cairo/cairo.scm.  
Notice that the helper includes the original C declarations as comments.

;; typedef struct _cairo_device cairo_device_t;
(define-fh-pointer-type cairo_device_t*)

;; union _cairo_path_data_t {
;;   struct {
;;     cairo_path_data_type_t type;
;;     int length;
;;   } header;
;;   struct {
;;     double x, y;
;;   } point;
;; };
(define cairo_path_data_t-desc
    (list `(header
                (list `(type ,cairo_path_data_type_t-desc)
                      `(length ,int))))
          `(point ,(bs:struct (list `(y ,double) `(x ,double)))))))
(export cairo_path_data_t-desc)
(define-fh-bytestructure-type/p cairo_path_data_t cairo_path_data_t-desc)
(define union-_cairo_path_data_t cairo_path_data_t)

;; typedef enum _cairo_path_data_type {
;; } cairo_path_data_type_t;
(define-fh-enum-type cairo_path_data_type_t

;; typedef void (*cairo_destroy_func_t)(void *data);
(define (wrap-cairo_destroy_func_t proc) ;; => pointer
 (ffi:procedure->pointer ffi:void proc (list '*))
(export wrap-cairo_destroy_func_t)

;; cairo_status_t cairo_device_set_user_data(cairo_device_t *device, const 
;;     cairo_user_data_key_t *key, void *user_data, cairo_destroy_func_t 
;;     destroy);
(define cairo_device_set_user_data
  (let ((~f (ffi:pointer->procedure
              (lib-func "cairo_device_set_user_data")
              (list '* '* '* '*))))
    (lambda (device key user_data destroy)
      (let ((~device (unwrap-cairo_device_t* device))
            (~key (unwrap-cairo_user_data_key_t* key))
            (~user_data (unwrap~pointer user_data))
            (~destroy (unwrap-cairo_destroy_func_t destroy)))
          (~f ~device ~key ~user_data ~destroy))))))
(export cairo_device_set_user_data)

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