Re: [PATCH v5 02/12] HID: pidff: Do not send effect envelope if it's empty

[Oliver Neukum <oneukum@suse.com>]

On 19.01.25 14:12, Tomasz Pakuła wrote:
> Envelope struct is always initialized, but the envelope itself is
> optional as described in USB PID Device class definition 1.0.
> 
> 5.1.1.1 Type Specific Block Offsets
> ...
> 4) Effects that do not use Condition Blocks use 1 Parameter Block and
> an *optional* Envelope Block.
> 
> Sending out "empty" envelope breaks force feedback on some devices with
> games that use SINE effect + offset to emulate constant force effect, as
> well as generally breaking Constant/Periodic effects. One of the affected
> brands is Moza Racing.

[..]
> @@ -261,10 +261,19 @@ static void pidff_set_envelope_report(struct pidff_device *pidff,
>   static int pidff_needs_set_envelope(struct ff_envelope *envelope,
>   				    struct ff_envelope *old)
>   {
> -	return envelope->attack_level != old->attack_level ||
> -	       envelope->fade_level != old->fade_level ||
> +	bool needs_new_envelope;
> +	needs_new_envelope = envelope->attack_level  != 0 ||
> +		             envelope->fade_level    != 0 ||
> +		             envelope->attack_length != 0 ||
> +		             envelope->fade_length   != 0;
> +
> +	if (!needs_new_envelope || !old)
> +		return needs_new_envelope;

I am afraid this is the most convoluted piece of boolean algebra I've seen
in a long time. In particular because it mixes things that do not belong together.

	Regards
		Oliver