Support enabling/disabling mouse/keyboard movement

[superdump]

I wanted to be able to enable/disable the FlyCamera movement systems so that I could use this crate for controlling the camera, and still be able to interact with UI elements.

I intend to use this with mouse_button_activate = Some(MouseButton::Right) and activate_is_toggle = false to work similarly to some other game engines I've used but I thought I'd make it a bit more flexible while I was at it. 😄

I've made it so that you can specify a mouse button or key to 'activate' motion, and then if activate_is_toggle is set, then pressing the button/key will toggle whether movement is activated, else if it is not set, you have to hold down the button/key for movement to be activated.

I also made the default be activate_is_toggle = true and no 'bindings' set, and the 'activate' state is true so that the default behaviour before this PR is preserved where movement is always on.

NOTE: This is based on PR #2 .

[mcpar-land]

I actually like the idea of a toggle quite a bit now that you mention it, but including a key-binding for it that must exist seems out of scope for the package.

Adding just a simple enabled bool would be sufficient, and having users program their own means of toggling wouldn't be super difficult, I imagine it's something you could do in just one system function.

[mcpar-land]

bevy_fly_camera/src/lib.rs

Line 70 in 882b5f2

pub enabled: bool,

bevy_fly_camera/src/lib.rs

Lines 131 to 143 in 882b5f2

	let (axis_h, axis_v, axis_float) = if options.enabled {
	(
	movement_axis(&keyboard_input, options.key_right, options.key_left),
	movement_axis(
	&keyboard_input,
	options.key_backward,
	options.key_forward,
	),
	movement_axis(&keyboard_input, options.key_up, options.key_down),
	)
	} else {
	(0.0, 0.0, 0.0)
	};

bevy_fly_camera/src/lib.rs

Lines 201 to 203 in 882b5f2

	if !options.enabled {
	continue;
	}