dinput: Add effect gain support

[Daniel Remenak]

On Mon, Jan 19, 2009 at 12:52 PM, Vincent Pelletier
<plr.vincent at gmail.com> wrote:
> dinput: Add effect gain support
>
> --
> Vincent Pelletier
>

Vincent,

This patch is ok as far as it goes, but not completely correct.

Firstly, SetParameters needs to apply the parameters to effects while
they are playing, not just store them.  Existing parameters are all
part of the effect structure, so that is taken care of automatically.
Since gain is handled by a different mechanism, you also need to
handle the while-playing case (unless DIEP_NODOWNLOAD is specified).
This probably means you need to implement GetEffectStatus, since you
won't want to apply the gain unless the effect is playing.

Secondly, the kernel's ff.txt suggests that evdev handles the gain
globally for the device.  Since the DirectInput definition of gain is
per-effect rather than per-device, you should also test what happens
when you set the gain differently in two simultaneously-playing
effects on the same device.  If Windows mixes them (i.e. truly applies
the gain per-effect) then we need to come up with some logic to do the
same (probably by scaling the effect envelope or magnitude, depending
on the effect type, and keeping it updated when the user modifies the
scaled parameters).

Thirdly, SetParameters still has a comment that says gain and sample
periods aren't supported.  Please update any applicable comments when
you update the code - outdated comments are worse than no comments at
all.

Regards,
Daniel Remenak