There is a game series called jelly car which has a physics system based around softbodies. The creator goes into detail on the whole entire physics engine in a youtube video. I watched it and was inspired to recreate his system. I have attempted softbodies in the past (see here, and here). They are based around a lot of the same principles. For example they both use nodes and springs to simulate the jelly effect. He also has a collision system that I had also made in another project (see it here). His system also adds some complexity to help stabilize the simulation. For example he adds frames and a volume constraint.
The volume constraint can be used to simulate balloons or tires. I wanted to implement the volume constraint because I believed it would be the easier of the two. This belief couldn't have been more wrong as the volume constraint has led my simulations to explode (as seen in the gif above) a lot while the frame keeps thing stable. This means way more debugging for the volume constraint. The volume constraint is a simple concept. You find the volume and based off how it compares to the initial volume you add forces to each point. For example if the volume is half of the initial volume then you want to add an outward force. To calculate the volume I break each shape into triangles. Using determinants you can easily calculate the area of a triangle. Find each area then add them all up. Then when adding the forces to each point you find the normal of each line making up the shape. Then add the forces based off the normal.
check it out here:
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