Geometry Nodes - Tilted Curve Boolean

Question

I'm trying to create a shape that is the boolean difference of a tilted curve and a cube using geometry nodes.

If the curve is not tilted (twisted) - the result is quite smooth and clean and quite acceptable:

If the curve has a tilt (twisted) like this example curve:

Then the result has horrible jagged edges. Even if I turn the resolution or resample the curve up to 128 or 256 it still looks horrible with jagged edges after the boolean operation.

Shade smooth OFF:

Shade smooth ON:

My node setup looks like this:

I understand it's not possible to do boolean operations using pure curves and there is some precision lost when converting to meshes.

There must be a way to get an acceptable result - how to get a cleaner result when doing boolean difference with tilted curve?

Update: To help visualize what I think is happening I created a curve with cube instances on points which is similar to the quadrilateral. With no twist you can see the inside of the curve is smooth. As soon as you introduce tilt to the curve it gets wonky.

Answer 1

And here is a completely different idea to create this shape, including a cutout inside:

Here I first create a basic shape using two curves, which I scale accordingly.

I then extrude this in height.

I scale the upper face that can be selected in this way with an individual center, so that I achieve the shape you sketched.

Finally I separate only the faces, so that I can achieve a different smoothing of the normals.

---

I have no idea if this is helpful, but I found this to be quite an interesting variation.

_{(Blender 3.2)}

Answer 2

Credit to @Nathan for his suggestion of Resampling the quadrilateral.

I found if you try to adjust the Resample Curve Count while the node is connected blender crashes almost every time if you drag the slider for the number to adjust the count. I had best results if I adjusted the count then connect the node or manually type in a fixed number rather than scrolling through numbers. It accepted numbers that were not multiples of 4 and rendered OK but didn't handle scrolling OK.

I had to turn the count up pretty high (128) to make it look less jagged.

It still leaves some artifacts with and without smooth shading on but the result is less jagged and more usable so I consider this an answer.

Answer 3

Here would be a variant that is not necessarily quite optimal, but at least it delivers:

• A clean mesh
• Neatly smoothed normals

The main changes to your example are that here I use a Curve Line as profile for Curve to Mesh, and clip this mesh with a Cube.

The resulting surface I send to the node Convex Hull, which creates a solid mesh from it.

Finally I apply the node Set Shade Smooth to the front faces (the curved faces).