Devlog #13

I added triangle-walls which vertices are 3 dynamic spheres, which can collide with other particles and have all 4 particles update with their own velocities!
This makes the engine a lot more flexible, so you don’t have to make big grids of spheres if you want to be able to have walls that can move, instead of being static. And it makes rigidbodies (probably) possible!

(Press enter to spawn balls)
Demo!

This devlog is a bit long, sorry! I didn’t want to go too far over 10 hours like a did a couple devlogs ago.

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2D

2D is, of course, simpler than 3D, and the length of the function for these walls definitely show that (~40 lines). I used the same algorithm to find the closest position on a line to another position as I used for detecting collisions on the edges of the static 3D walls a while ago. It gives you a lerpable value from from the first point to the second point of the line, and you can use that to find the point you are looking for. Comparing it to the circle you’re checking against, will give the distance and the normal of the collision. You can use that information to move the circle out of the wall, and push the wall away, using the value to lerp between as the ratio to push each of the points that the wall is made of away.

3D

This function is a bit more complicated, being about 80 lines long, but a lot of the information in the 2D version is applicable here too.

Here, instead of trying to find the closest point, we are trying to find the barycentric coordinates of the point, which is similar to the value to lerp between the two points in 2D, but for 3D (It’s basically just 3 numbers which tell you how close you are to each vertex of a triangle, and can describe any point on the triangle). This involves find the triangle’s area that you are checking against using the cross product, getting the distance of the point inward to the triangle for each edge, and calculating some inverse areas, which magically (not really) give you the barycentric coordinates. We then use these coordinates, as long as the distance to the triangle face using the dot product, to figure out whether the ball is colliding with the face, and if so, moving the ball outside of the triangle and moving the 3 vertices away as well, of course using each barycentric coordinate as a weight for how much to move each individual vertex.
I haven’t implemented detections with the edges of the triangles exactly yet though, only the faces, but I will try to implement it soon!