Weird results from lookAt

advanced
#1

why are some of these cubes Rolling? would expect them all to be evenly facing the origin like the middle column is.

Screen Shot 2016-07-14 at 12.27.00 AM.png784×1198 7.27 KB 

void ofApp::setup(){
    
    ofBackground(45,45,45);

 
}

void ofApp::draw(){
    cam.begin();
    ofEnableDepthTest();
    ofEnableLighting();
    pointLight.enable();
    
    material.begin();
    
    for(int j = -5; j < 5; j++){
        for(float i = 0; i < TWO_PI; i+= TWO_PI/12){
            ofBoxPrimitive box;
            box.set(0.5, 0.5, 0.5);
            box.setPosition(cos(i)*5, sin(i) *5, j);
            box.lookAt(ofVec3f().zero(), ofVec3f(0,1,0) );
            box.draw();
        }
    }
    
    
    material.end();
    ofDisableLighting();
    ofDisableDepthTest();
    cam.end();
}
#2

I set the upvector to (0,0,-1) and I’m getting more of the results I would expect but there are still some weird stragglers in the group, look at the slight roll in the center column midway down

Screen Shot 2016-07-14 at 12.49.21 AM.png1334×1260 8.71 KB

#3

They are rolling because they are not on the same plane as the lookAt, the y axis is changing, while the y axis of the lookAt is always the same.

#4

I thought the point of the lookAt function was: given an object and an arbitrary point in space, make the object face that point in space

That makes me think there shouldnt be roll involved. I guess the function I’m imagining takes an up vector and a forward vector for the object it’s reorienting

#5

You could also do this with a Quaternion;
take the vector they are facing before the transform ( 0, 0, 1) as argument one and the vector between the target and their position as argument two.

code is from memory - might need tweaking:

ofQuaternion q; 
q.makeRotate( ofVec3f(0, 0, 1),  box.getPosition() * -1.0 ); 
box.rotate(q);