CODEWITHSUNDEEP
c++box2d
HalloweenJack
HalloweenJack

Reputation: 281

Box2D object position won't be affected by velocity changes

I have previously used Box2D, so this code I'm using is already functional on another project, the only major difference is that the world isn't being passed as a paremeter, it's given as a Global Pointer.

When I apply the Linear Velocity (which I have already tried from 1 to 99999 and still nothing), not even the position on world getting it by Obj1->Body2D->GetPosition().x; will have any change.

Main:

GameObject Obj1 = new GameObject(iVec2(500), iVec2(30));
void Update() {
    Obj1->b2_body->SetLinearVelocity(b2Vec2(5, 0));
    //Still same Position on Obj1
    //Camera Update
    Obj1->Render(*Renderer);
}

Script 1:

std::unique_ptr<b2World> World = std::make_unique<b2World>(b2Vec2(0.0f, 9.81f));

Script 2:

extern std::unique_ptr<b2World> World;

GameObject::GameObject(iVec2 position, iVec2 size, Texture sprite, iVec3 color)
    :Position(iVec2(position.x / 128.0f, position.y / 128.0f)), Size(iVec2(size.x / 128.0f, size.y / 128.0f)) {
        this->RenderPosition = position;
        this->RenderSize = size;

        b2BodyDef b2d_BodyDef;
        b2d_BodyDef.type = b2_dynamicBody;
        b2d_BodyDef.position.Set(Position.x, Position.y);
        b2d_Body = World->CreateBody(&b2d_BodyDef);

        b2PolygonShape b2d_BoxShape;
        b2d_BoxShape.SetAsBox(Size.x / 2, Size.y / 2);

        b2FixtureDef b2d_FixtureDef;
        b2d_FixtureDef.shape = &b2d_BoxShape;
        b2d_FixtureDef.density = 1.0f;

        b2d_Fixture = b2d_Body->CreateFixture(&b2d_FixtureDef);
    }

void GameObject::Render(Renderer2D & renderer) {
        float tempPosX = this->b2d_Body->GetPosition().x;
        float tempPosY = this->b2d_Body->GetPosition().y;
        this->RenderPosition = iVec2((tempPosX - Size.x / 2) * 128.0f, (tempPosY - Size.y / 2) * 128.0f);
        this->RenderSize = iVec2(Size.x * 128.0f, Size.y * 128.0f);
        renderer.Render(this->Sprite, this->RenderPosition, this->RenderSize, this->RealRotation, this->Color);
}

Upvotes: 0

Views: 98

Answers (1)

Louis Langholtz
Louis Langholtz

Reputation: 3123

Per the conversation in the comments... if the world Step method isn't called, then object positions won't update.

Add a call like:

World->Step(timeStep, velocityIterations, positionIterations);

Put it in a loop to get object positions to update based on their properties like their velocities.

iforce2d has produced a tutorial on Box2D worlds (including use of their step method) that I recommend for anyone who wants to learn more about the Box2D b2World class.

Hope this helps!

Upvotes: 1

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