type+value arguments for dynamic APIs;  see: doc/ref/arg.html


typedef struct mbtk_arg_s mbtk_arg_t;

typedef struct mbtk_color_s {
  unsigned char r, g, b, a;
} mbtk_color_t;

typedef enum mbtk_value_type_e {
  MBTK_INVALID,
  MBTK_BOOL,
  MBTK_LONG,
  MBTK_ULONG,
  MBTK_DOUBLE,
  MBTK_STRING,
  MBTK_COORD,

  /* modifiers: */
  MBTK_ARG_DELTA = 0x100,
  MBTK_ARG_MULT = 0x200
} mbtk_value_type_t;

#define MBTK_ARG_MASK_BASE 0xFF

struct mbtk_arg_s {
  mbtk_value_type_t type;
  union {
    int b;
    long int l;
    unsigned long int ul;
    double d;
    const char *s;
    struct { /* on a typical 32 or 64 bit system this should be 2*32 bits, same as sizeof(double) */
      int x;
      int y;
    } c;
  } v; /* value */
};


/* Setters returning 0 on success; set native value from arg */
int mbtk_arg_set_int(int *dst, const mbtk_arg_t *src);
int mbtk_arg_set_short(short int *dst, const mbtk_arg_t *src);
int mbtk_arg_set_uchar(unsigned char *dst, const mbtk_arg_t *src);
int mbtk_arg_set_schar(signed char *dst, const mbtk_arg_t *src);
int mbtk_arg_set_color(mbtk_color_t *dst, const mbtk_arg_t *src);
int mbtk_arg_set_bool(mbtk_bool_t *dst, const mbtk_arg_t *src);

/* Getters return 0 on success; get arg from native value */
int mbtk_arg_get_int(mbtk_arg_t *dst, int src);
int mbtk_arg_get_short(mbtk_arg_t *dst, int src);
int mbtk_arg_get_uchar(mbtk_arg_t *dst, unsigned char src);
int mbtk_arg_get_schar(mbtk_arg_t *dst, signed char src);
int mbtk_arg_get_color(mbtk_arg_t *dst, mbtk_color_t src);
int mbtk_arg_get_bool(mbtk_arg_t *dst, mbtk_bool_t src);


/* Wrappers for combined get and set */
int mbtk_arg_getset_int(int *nat, mbtk_arg_t *get, const mbtk_arg_t *set);
int mbtk_arg_getset_short(short int *nat, mbtk_arg_t *get, const mbtk_arg_t *set);
int mbtk_arg_getset_uchar(unsigned char *nat, mbtk_arg_t *get, const mbtk_arg_t *set);
int mbtk_arg_getset_schar(signed char *nat, mbtk_arg_t *get, const mbtk_arg_t *set);
int mbtk_arg_getset_color(mbtk_color_t *nat, mbtk_arg_t *get, const mbtk_arg_t *set);
int mbtk_arg_getset_bool(mbtk_bool_t *nat, mbtk_arg_t *get, const mbtk_arg_t *set);


/* Convert a to a string; if a's type is string, just return the string
   field, else render into out and return that. */
const char *mbtk_arg_print(char *out, int outlen, const mbtk_arg_t *a);

MBTK_INLINE mbtk_arg_t mbtk_arg_long(long l)        { mbtk_arg_t a; a.type = MBTK_LONG; a.v.l = l; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_long_delta(long l)  { mbtk_arg_t a; a.type = MBTK_LONG | MBTK_ARG_DELTA; a.v.l = l; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_long_mult(long l)   { mbtk_arg_t a; a.type = MBTK_LONG | MBTK_ARG_MULT; a.v.l = l; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_dbl(double d)       { mbtk_arg_t a; a.type = MBTK_DOUBLE; a.v.d = d; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_dbl_delta(double d) { mbtk_arg_t a; a.type = MBTK_DOUBLE | MBTK_ARG_DELTA; a.v.d = d; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_dbl_mult(double d)  { mbtk_arg_t a; a.type = MBTK_DOUBLE | MBTK_ARG_MULT; a.v.d = d; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_str(const char *s)       { mbtk_arg_t a; a.type = MBTK_STRING; a.v.s = s; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_str_delta(const char *s) { mbtk_arg_t a; a.type = MBTK_STRING | MBTK_ARG_DELTA; a.v.s = s; return a; }
MBTK_INLINE mbtk_arg_t mbtk_arg_str_mult(const char *s)  { mbtk_arg_t a; a.type = MBTK_STRING | MBTK_ARG_MULT; a.v.s = s; return a; }