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Pretty sure that there is some answer to this already somewhere since it seems such a basic action. But I could not find an answer to it. Maybe since I just started with Blender, I just don't know the relevant keywords for it. I try to let some Tetris blocks fall on to each other. But for some unclear reasoning, the collision happens in mid-air. Rather then on the surfaces of the two rigid objects. I've made a video to see what does happen.

Both objects only have a rigid body set in the Physics tab, with the following parameters:

Rigid Body

  • Type: Active, Dynamic
  • Mass: 1

Rigid Body Colisions

  • Shape: Convex Hull
  • Source: Deform
  • Friction: 1
  • Bounciness: 0
  • Collision margin: 0
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    $\begingroup$ +1 for providing a video and detailed info in your question, right off the bat. I wish more people asked questions this way ;-) $\endgroup$
    – dr. Sybren
    Commented Mar 5, 2018 at 11:12

1 Answer 1

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There is a difference between the shape of the mesh, and the shape used for collision detection. Often a mesh is too complex to allow for real-time collision detection.

What you "see" is the convex hull of the Tetris block. It's basically the shape that you'd get when wrapping a shape with an elastic band (in 2D) or elastic sheet (in 3D). In this image, the green shape is the convex hull of the black shape:

Convex Hull

The Convex Hull is easy to do physics sims with. It's also quite predictable, since objects cannot hook into each other and will be able to slide off of each other. If you want to have the exact shape of the object used for the collission detection, use the "Mesh" choice. Since your meshes are simple Tetris blocks (compared to, say, high-polygon, detailed game characters) this should work fine.

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  • $\begingroup$ Thank you for your explanation, I understand now what happens. That is very delightful :-). The problem of "weird" behaviour now shifts to extensive bounciness, when the 2 shapes come into contact with each other. What settings should I like into. To modify this behaviour? $\endgroup$
    – user007
    Commented Mar 5, 2018 at 18:50
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    $\begingroup$ @user007 Please ask this as a different question; it's quite different to this one. Feel free to provide a link here if you want. $\endgroup$
    – wizzwizz4
    Commented Mar 5, 2018 at 19:07

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