[Libff-devel] API suggestion: feature queries

[Johann D. <de...@if...>]

Hi there !

Here is a first proposal for the API.

/* Describes a force feedback device
*/
struct ff_device;

/* Related functions */
/* Get a list of available devices on the system */
ff_device_list ff_enumerateDevices();

/* Test if an effect is supported */
bool ff_effectIsSupported(ff_device, ff_effectCapability);

ff_effectCapability would be a pair <effect, feature>. Sample pairs 
would be:
- <FF_CONSTANT, FF_ANY> to check if constant effects are supported
- <FF_CONSTANT, FF_ANY_DIRECTION> to check if constant effects can have 
any direction (not true for wheels, for example)
- <FF_RUMBLE, FF_DIRECTION> to check if rumble effects can have 
direction (I guess it's generally not the case)
- <FF_SINE, FF_UPDATE> to check if it's possible to update a sine wave 
effect while it's playing
- <FF_ALL, FF_PAUSE> to check if it's possible to pause any kind of effect
- and so on, there are many possible combinations
Note the special values FF_ANY and FF_ALL. They can be seen as kinds of 
quantifiers (FF_ANY = exists, FF_ALL = for all). For example, to test if 
a device has any ff capability at all, one could use <FF_ANY, FF_ANY> 
(that's useless though, because ff_enumerateDevices() should not return 
non-ff capable devices)
We could even use these pairs to express constraints and find all the 
devices matching those constraints. But that's for later, I think. We 
need to keep it simple at first, but let's keep this possibility in our 
minds.


/* Return the number of effects that can be played at the same time
*/
int ff_effectsNumber(ff_device);

Note that it's possible that several processes access a device. In that 
case, the actual number of effects playable at the same time may be 
lower. You may wonder what is the use of having several processes 
accessing a device. That's probably not meaningful for joysticks, but it 
is for mice.

-- 
Johann Deneux

 
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