position-based-dynamics VS DART

If you are already familiar with opengl, then you don't actually need a soft body sim open source project that is written with opengl to understand how to implement soft body sim in opengl. Basically, what I mean by this is that for soft body simulations, vertices may deform by many transformations including, but not exclusively, rigid transformations (soft bodies can deform in highly non-linear ways, you can stretch them in many ways, twist them, etc). This means that you cannot simply animate your objects with a rotation and a translation as you would animate rigid bodies. You will need to update vertex positions every frame and transfer them to opengl for rendering. So in other words, you only need an open source project which solves the problem of computing new vertex positions at every frame given external and internal forces. There are many different algorithms for simulating soft bodies, (algorithms which compute new vertex positions at every frame), but I would suggest targeting position based dynamics, which is one of the simpler but more flexible real-time methods for simulation. It is used in many real time scenarios such as video games. I believe there are many open source projects which implement position based dynamics, but if you can't find them or do not find them to your liking, you can try this one https://github.com/Q-Minh/position-based-dynamics. It is a prototype of PBD that you can play with in ImGui and uses libigl for visualization. libigl's viewer actually wraps opengl code. But as I said, you only need a way to find and update new vertex positions and send those to opengl regularly to integrate the soft body sim to opengl. Hope this helps.

DART (Dynamic Animation and Robotics Tookkit)