Hello, i have a problem concerning arcball.
I managed to implement it, and it works. But on the other hand, i wanna implement a constant object, something which is inside the arcball, but stays on his place. A rotation against the arcball rotation was my idea.
I tried this with multiplying the modelview matrix with a “reverse matrix”, which i get from a quaternion from the normal arcball matrix but with the difference that i multiplied it with -1 , so that it gives you a kind of “contra-rotation” against the arcball rotation.
It works in the beginning but if i stop to drag, and i retry it, there coordinate-system seems to have changed, but only for the fixed object, the other ones which i want to rotate with arcball is working really fine.
I am sorry for the confusing description, but if somebody understand the problem, and knows a hint for me, would be great.