Restricted

[Megidd]

Play around to come up with a restricted pack rather than a 3D one.

What's restricted?

Assume there is a 3D print floor. The Z axis is upward. The only transformations allowed are moving along X and Y and rotating around Z axis. That's what we mean by 2D pack.

[Megidd]

3D example

With this file as input for VS Code debugger, the 3D packing result is as follows.

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Launch Package",
            "type": "go",
            "request": "launch",
            "mode": "auto",
            "program": "${fileDirname}",
            "args": ["4", "3DBenchy.stl", "2", "Pharaoh.stl", "10", "Utah_teapot_solid.stl"],
        }
    ]
}

1st iteration of Simulated Annealing

2nd iteration of Simulated Annealing

3rd iteration of Simulated Annealing

[Megidd]

There is a Rotations variable:

https://github.com/fogleman/pack3d/blob/4c6f72b19a7688cfc90e933fd7d4a5c3ed30a5a0/pack3d/model.go#L10

Looks like it determines the available options for orienting 3D models. Maybe we can reduce 3D behavior to 2D behavior by limiting the options of Rotations variable.

Limiting rotations

After limiting rotations, now the Simulated Annealing results are like these:

[Megidd]

Z axis translation

After limiting the Rotations variable, the Simulated Annealing algorithm is still moving the objects along the Z axis. Such a movement is not allowed for our 2D case.

It's needed to find a way to prevent translation along Z axis.

[Megidd]

Prevent move along Z

After preventing the translation along the Z axis, the Simulated Annealing results look like these:

[Megidd]

Test

After introducing a restricted mode, the test is still as before:

[Megidd]

Mesh origin: bottom-center

After setting mesh local origin to bottom-center of bounding box, rather than center of b-box, the results look generally fine. But there are collisions between objects:

[Megidd]

Mesh origin: center

When mesh local origin is at the center of bounding-box, no collision is observed between objects. Apparently, the logic has specific assumptions about mesh local coordinate system origin.

[Megidd]

Reasonable assumption

It looks reasonable to assume the mesh origin to be located at center of b-box. Makes sense. It's apparently a sensible general requirement. Let's go with it? 🙄

[Megidd]

Collision bug 🐞

For 3D print on a floor, it's desired to align the bottom of all the 3D models with each other. So, let's try to see if this collision bug can be fixed:

#1 (comment)

[Megidd]

Maybe the collision bug is due to the fact that while building BVH, the mesh.Center() is called again:

https://github.com/fogleman/pack3d/blob/4c6f72b19a7688cfc90e933fd7d4a5c3ed30a5a0/pack3d/bvh.go#L9

Would the bug be fixed if mesh.Center() is commented out?

[Megidd]

Fix collision bug 🔧

Collision bug is fixed.

Before

After

No collision is observed ✔️

[Megidd]

Optimize

Many suggested optimizations are applied.

Test

3D mode

Restricted mode