Entity knockback

[Mayhaw]

Hi, can someone please tell me how to add knock-back? My entities have x,y,velocityX and velocityY variables, and i have just no idea how to add it. I can like add 5 to velocityX for example, but how do i decrease it? And if the entity has bumped into something and it's velocity is set to 0, how do i make it so that it stops decreasing?Maybe add separate fields, but that destroys the purpose of one velocity vector, doesn't it? Please help me :c


PS: Using Artemis.

[kalkitus]

It's probably a bad way of doing it, but this is my code for knockback to give you an idea

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public void knockback(float r, float force){       r = r - 180;             force *= knockbackResistance; // how heavy the entity is (so lesser knock back)             knockbackTimer = force * 8;       knockbackTo = new Vector2((force * (float) MathUtils.sin(r * MathUtils.degreesToRadians)),                          (-force * (float) MathUtils.cos(r * MathUtils.degreesToRadians)))                                        .add(position);                    }

Then I have this on the update loop for the entity

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public void update(){       if(knockbackTimer > 0){          position = Tools.lerp(position, knockbackTo, 0.2f);          knockbackTimer -= Gdx.graphics.getDeltaTime() * 1000;       }         }

[Mayhaw]

Whoa i didn't expect code! Thanks  ! I think i will add knockbackTimer an knockbackTo to the Velocity component and do the logic in some system. Thanks again  !

PS : r is radians , right? Or degrees?

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[CaptainJester]

I would recommend against having knockback specifically in the entity. Instead you should have an acceleration attribute. You could just use a vector for acceleration. You then apply acceleration to speed every update. Then you apply friction to acceleration right after. This way anything that affects the entity can just change acceleration.

[Riven]

Please note that applying friction to acceleration makes no sense. Apply it to velocity. Acceleration (caused by a force) is immediately zero after it is processed, as the knockback force is instantaneous.

Instead of having an acceleration vector as field(s), I'd do this:

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class Entity {    Vec2 position;    Vec2 velocity;    float mass;    Vec2 force;    float drag;    public void tick() {       Vec2 acceleration = new Vec2(force).div(mass);       force.set(0,0,0);       velocity.add(acceleration);       position.add(velocity);       velocity.mul(1.0f - drag);    } }

Whether this fits in your game logic, is another matter

[ClickerMonkey]

According to Riven's logic, also ensure tick() is being called at a consistent rate (like 30fps or something).

[Riven]

Ah, yes. I have this assumption that everybody is sensible enough to have a fixed logic rate, and a dynamic render rate.

(Please don't let this derail in a fixed/delta step discussion!)