Le 2022-08-06 20:55, Ralph Little a écrit :
Hi,
On 2022-08-06 10:35, Thierry Huchard wrote:
Le 6 août 2022 18:17:12 GMT+02:00, Ralph Little <[email protected]> a
écrit :
Hi,
I'm having a go at writing my first SANE backend for a learning
exercise.
I notice that a few backends that use the functions:
sanei_usb_attach_matching_devices() and sanei_usb_find_devices()
require some context information in the callback function to complete
the find function.
This is typically because the backend is looping through a list of
known device configurations and calling the sanei_* function on each
one: the callback needs to know the element in that loop to complete
the attach function in the callback.
This is typically achieved with setting some global variables to be
picked up by the callback function, or searching again through the
original loop using information gleaned from the devicename (such as
vendor and product), both of which are messy and ugly hacks.
I propose that we change the function signature of the functions and
the callback to include a (void *) context pointer:
SANE_Status
sanei_usb_find_devices (SANE_Int vendor, SANE_Int product, void
*context,
SANE_Status (*attach) (SANE_String_Const dev, void
*context));
void
sanei_usb_attach_matching_devices (const char *name, void *context,
SANE_Status (*attach) (const char *dev, void
*context));
Hi Ralph,
Your change may impact proprietary backends (Brother, Canon, ...).
Thierry
That is a good point.
We could introduce additional functions with the above signatures
(e.g. sanei_usb_find_devices2()) but I feel that to be an
unsatisfactory solution.
Any other suggestions/comments welcome.
it would be possible to add a pointer at the beginning of the file and
to access this data using the get and set methods:
static void *data_device = NULL;
void sanei_usb_devices_data_set (void *data);
void *sanei_usb_devices_data_get (void);
Cheers,
Ralph
