Add gamepad trigger press values.

[bhickey]

This fixes #680.

[cart]

I think this is a good addition, but I think its worth ensuring this is a good "general purpose" api and not just something for gamepad buttons.

Some questions to answer:

• should we be setting value to 1.0 when a key is pressed and 0.0 when a key is released?
• if so, should value be the "source of truth" for the "pressed" value? Ex: the "press" state is directly derived from the "value". This could be expanded to allow for configurable "thresholds" (aka: pressed is only set when value is between 0.5 and 1.0)
• Should such an api be implemented at a higher level? ex: something like bevy_input_map

[simpuid]

No one is stopping us from using Axis<GamepadButton> resource. But still this is also a valid approach.

should we be setting value to 1.0 when a key is pressed and 0.0 when a key is released?

Key state is derived from these values not the other way around. And the range could be -1.0 to 1.0 instead of 0.0 to 1.0 as it was in my case, that's why the plugin queries the gamepad for default values of axes on connect event.

if so, should value be the "source of truth" for the "pressed" value? Ex: the "press" state is directly derived from the "value". This could be expanded to allow for configurable "thresholds" (aka: pressed is only set when value is between 0.5 and 1.0)

GilrsBuilder supports this but only at initialization. We can implement our own filters at bevy_gilrs level and that can be updated the way we want.

Should such an api be implemented at a higher level? ex: something like bevy_input_map

I don't think so, because Input<GamepadButton> should work without bevy_input_map plugin and we need these values for proper functioning.

[bhickey]

Closing in favor of #683