Organic cell-like motion with ofxBox2d?

@t.espinoza wrote:

hi all! trying to computationally understand my problem. i want to make this cell-like shape that shifts around organically, maybe something similar to metaballs?

right now, i’m using ofxbox2d and connecting ofxbox2d circles to each other with joints, and eventually connecting the last one to the first one to close the shape:

    for (unsigned int i = 0; i < circles.size(); i++)
    {
        auto joint = std::make_shared<ofxBox2dJoint>();
        
        if (i == 0)
        {
            joint.get()->setup(box2d.getWorld(), circles[circles.size()-1].get()->body, circles[i].get()->body);
        }
        else
        {
             joint.get()->setup(box2d.getWorld(), circles[i-1].get()->body, circles[i].get()->body);
        }
        
        joint.get()->setFrequency(4.0);
        joint.get()->setDamping(0.5);
        joint.get()->setLength(ofRandom(40, 74));
        joints.push_back(joint);
    }

this seems to work fine to me. i run into issues when trying to articulate the motion, however. i thought i’d be able to do it by adding a repulsive force to each circle that pushes it away from the circle that’s closest to it:

void ofApp::applyForce(std::vector<std::shared_ptr<ofxBox2dCircle> > circleVector)
{
    for (int i = 0; i < circles.size(); i++)
    {
        float minDistance = 50;
        int closestIndex;
        
        glm::vec2 currentPos;
        glm::vec2 closestPos;
        
        currentPos = glm::vec2(circles[i].get()->getPosition().x, circles[i].get()->getPosition().y);
        
        for (int j = 0; j < circleVector.size(); j++)
        {
            float distance;
            glm::vec2 otherPos;
            
            if (j != i)
            {
                otherPos = glm::vec2(circleVector[j].get()->getPosition().x, circleVector[j].get()->getPosition().y);
                
                distance = glm::distance(currentPos, otherPos);
                
                if (distance < minDistance)
                {
                    closestIndex = j;
                    minDistance = distance;
                }
            }
            
            // std::cout << minDistance << std::endl;
            float force = ofMap(minDistance, 0, 50, 0.5, 0.1);
            force = ofClamp(force, 0.1, 0.5);
            
            circles[i].get()->addRepulsionForce(otherPos, force);
        }
    }
    
}

but they all just push each other to the bounds and i get end up with this:

not_a_blob.png1136x902 21.7 KB

i think intuitively i understand what’s happening – am also having trouble putting that into words – but i’m having a hard time figuring out how to translate the motion i want into code. would love to tap into everyone’s collective experience and help me navigate this issue

Posts: 1

Participants: 1

Read full topic