ELMVal

ELMVal.cs

/*
ELM (Eased Linear Motion) Value
Matches the start-end time of a linear motion curve with constant velocity,
but has motion easing and constant acceleration.
Can set target once, or every update.
*/
public struct ELMVal {
	private float _target_vel; //target velocity
	private float _t; //time in current curve
	private float _t_max; //max time of current curve
	private float _start,_end,_current; //starting, ending and current values
	private Vector2 _dval; //last update value delta, x is last timestep and y is value delta
	private Vector2 _nhalf_cp1; //normalized*0.5 point used for quadratic bezier curve control point 1
	
	public static ELMVal cons() {
		return new ELMVal(){
			_target_vel = 1,
			_nhalf_cp1 = new Vector2(0.5f,0)
		};
	}

	public ELMVal set_target_vel(float val) { _target_vel = val; this.set_target(this.get_target()); return this; }

	public float get_current() { return _current; }
	public void set_current(float val) { 
		_current = val; 
		this.set_target(this.get_target());

	}

	public float get_target() { return _end; }
	public bool get_finished() { return _t >= _t_max; }

	public float get_target_vel() { return _target_vel; }
	public void set_target(float target) {
		_end = target;
		_start = _current;
		_t = 0;
		_t_max = Mathf.Abs(_end-_start)/_target_vel;

		if (_dval.magnitude > 0) {
			_nhalf_cp1 = new Vector2(_dval.x,Mathf.Abs(_dval.y));
			_nhalf_cp1.Normalize();
			_nhalf_cp1.Scale(new Vector2(0.5f,0.5f));
		} else {
			_nhalf_cp1 = new Vector2(0.5f,0);
		}
	}
	
	public float i_update(float dt) {
		float prev_current = _current;
		_t = Mathf.Clamp(_t+dt,0,_t_max);
		float lerp_t = 1;
		if (_t_max != 0) {
			lerp_t = SPUtil.bezier_val_for_t(
				new Vector2(0,0),
				_nhalf_cp1,
				new Vector2(0.5f,1),
				new Vector2(1,1),
				_t/_t_max
			).y;
		}
		_current = SPUtil.lerp(_start,_end,lerp_t);
		_dval.x = dt;
		_dval.y = _current - prev_current;
		return _current;
	}
}