Coreaction - another solution for "multi-state" in game

I've been working with some Platfomer2D games, and I've used StateMachine for Character control. At the begining of the project, I thought the StateMachine will just simple like this :

But then, when project grew up, I got some mess like this :

The weakness of StateMachine

I see that, StateMachine has some weak points

"Single thread"

There's only one State can be run at a time, and we have to do many things in that state, and also checking to transition to other states

Hard to extend

When I want to add another state, I have to modify the other states too, because they're strong coupling together.

Learn from Unity's Animator component

Look at Unity's Animator component, I see there're two definition : The parameters and Transition conditions We define some parameter, we declare the transition between States, then, we just modify the value of Parameters (via SetTrigger(), SetFloat(), SetBool() .v.v..) and the Animator will select the right State to run, base on conditions.

The idea about Co-reactions

Here's a very simple Platformer2D, the character just have moving and jump action.

There're 2 reaction : Moving and Jump

Moving

• Action : add horizon force to make character moving

• Condition :

  Player hold A or D key (Input.GetKey(A || D) = true)

Jump

• Action : add vertical force to make character jumping

• Condition :

  Player press W(Input.GetKeyDown(A || D) = true)

  Player are on ground (OnGround = true)

From idea to script

And this's is how I declare the reaction for character

Define Parameters

ReactionController reactionCtrl = gameObject.AddComponent<ReactionController>();

reactionCtrl.AddParameter(ParameterID.OnGroundState, ParameterType.Boolean, false);
reactionCtrl.AddParameter(ParameterID.HoldLeftKey, ParameterType.Boolean, false);
reactionCtrl.AddParameter(ParameterID.HoldRightKey, ParameterType.Boolean, false);
reactionCtrl.AddParameter(ParameterID.PressJumpKey, ParameterType.Trigger);

Write the basic Action that will be used in Reaction

void Jump()
{
	var velo = controlRigidbody.velocity;
	velo.y = jumpSpeed;
	controlRigidbody.velocity = velo;
}

void Move(float XaxisRaw)
{
	var velocity = controlRigidbody.velocity;
	velocity.x += movingAccelerate * XaxisRaw * Time.deltaTime;
	controlRigidbody.velocity = velocity;
}

void RevertRender(bool isToLeft)
{
	var localScale = transform.localScale;
	var ratio = isToLeft ? -1f : 1f;
	localScale.x = Mathf.Abs(localScale.x) * ratio;
	transform.localScale = localScale;
}

Define Reaction, create conditions from parameters

void AddJumReaction()
{
	var jump = new BaseReaction();
	jump.AddCondition(ParameterID.PressJumpKey, CompareType.Trigger, null);
	jump.AddCondition(ParameterID.OnGroundState, CompareType.BooleanTrue);
	jump.SetAction(Jump);
	_reactionCtrl.AddReaction(jump);
}

void AddMoveLeftReaction()
{
	var moveLeft = new BaseReaction();
	moveLeft.AddCondition(ParameterID.HoldLeftKey, CompareType.BooleanTrue);
	moveLeft.AddCondition(ParameterID.VeloX, CompareType.FloatGreater, -movingLimitSpeedX);
	moveLeft.SetAction(() => Move(-1f));
	_reactionCtrl.AddReaction(moveLeft);
}

void AddMoveRightReaction()
{
	var moveRight = new BaseReaction();
	moveRight.AddCondition(ParameterID.HoldRightKey, CompareType.BooleanTrue);
	moveRight.AddCondition(ParameterID.VeloX, CompareType.FloatLess, movingLimitSpeedX);
	moveRight.SetAction(() => Move(1f));
	_reactionCtrl.AddReaction(moveRight);
}

From then, It'll easier for me when I want to add more reactions, or more condions or parameters. My demo is very simple, here I just paste some main part of my code.