Tutorial 3: Smooth, Broken, and Sharp Point Modes

Every control point on the profile curve has a mode that controls how the curve behaves through it. There are three modes, mirroring the conventions you already know from Adobe Illustrator and Figma:

Smooth — handles linked, the curve flows continuously
Broken — handles independent, you get a corner with tangent control on each side
Sharp — no handles, the curve passes through as a hard corner

Understanding when to use each mode is key to creating professional-looking profiles.

What you'll learn

The difference between Smooth, Broken, and Sharp point modes
How to toggle the mode on any control point with the three-way picker
The fastest way to break tangency: Alt + drag a handle
When each mode creates the best results
How mode affects the Bézier handles and what happens when you switch back

Prerequisites

Completion of Tutorials 1 and 2 is recommended.
Open a G-code Sculptor project with at least 3 control points.

Step 1: Identify the current mode

Step 1

Select a control point

Click any interior control point on the profile canvas. When selected, look at the Profile Points table below the canvas (or the floating selection toolbar). You will see three mode buttons side by side — Smooth, Broken, Sharp — with the current mode highlighted.

By default, new points are set to Smooth mode. In this mode, the curve passes through the point with continuous, flowing tangent lines — like a ribbon draped over the point.

Step 2: Understand Smooth mode (G1 continuity)

In Smooth mode:
- The curve enters and exits the point at matching angles.
- Two Bézier handles appear (small dots connected by thin lines), one on each side of the point.
- Moving one handle automatically mirrors the direction of the opposite handle while keeping each side's length independent.
- The result is organic, flowing shapes — perfect for vases, bottles, and sculptural forms.

Step 2

Observe the smooth curve

With an interior point selected, notice the two handle dots on either side. The curve flows through the point without any abrupt direction change. Drag the green (outgoing) handle and watch the amber (incoming) handle mirror its direction on the opposite side. This is Smooth mode at work.

Step 3: Switch to Sharp mode

Step 3

Toggle to Sharp

In the mode picker, click the Sharp button (corner icon). The Bézier handles disappear and the curve now makes a hard angle at that point.

In Sharp mode:
- The Bézier handles are removed (set to zero length).
- The curve arrives at the point from one direction and leaves in a potentially different direction.
- This creates a visible corner or kink in the profile.

Watch the 3D viewport — the shape now has a distinct edge where the sharp point sits, like the shoulder of a geometric vase.

Step 4: Discover Broken mode (the in-between)

Sometimes you want a corner at the point but still have tangent control on each side — for example, a smooth approach into a hard transition out, or two different curvatures meeting at a single anchor. That is exactly what Broken mode is for.

Step 4

Break the tangency without leaving the canvas

Select a Smooth point. Hold Alt and drag one of its handles. The point automatically promotes to Broken on the first frame of the drag — only the handle you grabbed moves, the opposite handle stays put. Release. The mode picker now highlights Broken, and the handle link lines render dashed with a small chevron marker on the anchor.

In Broken mode:
- Both handles still exist — you can shape each side independently.
- There is no automatic mirroring. Drag either handle freely without disturbing the other.
- The curve arrives along the incoming handle and leaves along the outgoing handle — those two directions are no longer constrained.
- Visually, the link lines between anchor and handles are dashed (instead of solid) and a small chevron sits on the anchor so you can spot Broken points at a glance.

Step 5: Switch a Broken point back to Smooth

Step 5

Re-link the handles

With a Broken point selected, click the Smooth button in the mode picker. The handles re-link, but their lengths are preserved — only their directions average out so they sit on a common tangent line again. You don't lose the curvature you spent time on; you just snap the two sides back into G1 alignment.

This makes Smooth ↔ Broken a non-destructive round-trip: you can experiment with breaking tangency, decide it was too much, and go back without rebuilding handles from scratch.

Step 6: Compare the three visually

Step 6

Cycle through the modes

Click the three buttons in turn — Smooth, then Broken, then Sharp — on the same point and watch how the curve and the 3D preview change:
- Smooth — flowing, organic transition
- Broken — corner with independent tangent control on each side
- Sharp — crisp geometric edge, no handles

Step 7: Build a geometric profile with Sharp mode

Step 7

Create a stepped vase

Set up a 5-point profile. Set all interior points to Sharp mode:
1. Bottom point — radius 25 mm
2. Sharp point at 30% height — radius 25 mm
3. Sharp point at 30% height — radius 35 mm (create a horizontal step)
4. Sharp point at 70% height — radius 35 mm
5. Top point — radius 35 mm

The result is a cylindrical vase with a sharp step outward at 30% height.

Step 8: Mix all three modes on the same profile

The real power comes from combining all three modes in one design:

Step 8

Create a mixed-mode profile

Start with 5 points:
1. Bottom point — radius 20 mm
2. Point at 30% height — Sharp mode, radius 30 mm (geometric base shoulder)
3. Point at 50% height — Broken mode, radius 35 mm (Alt-drag the outgoing handle to flatten the upper side while keeping the lower side curved)
4. Point at 70% height — Smooth mode, radius 30 mm (organic neck)
5. Top point — radius 22 mm

The profile now has a crisp angular base, a controlled flatten-and-curve transition in the middle, and a flowing organic neck above.

This mixed approach is how you create designs with architectural precision at the base, controlled transitions in the middle, and organic beauty at the rim.

Step 9: Understand what happens to handles when modes change

When you switch modes, the handles behave differently:

Transition	What happens
Smooth → Broken	Handles stay where they are. They simply unlink — drag either freely without affecting the other.
Smooth → Sharp	Handles collapse to zero. The curve becomes angular at that point.
Broken → Smooth	Handles reconcile: directions average onto a common tangent, lengths preserved. Curvature on each side is kept as close to what you had as possible.
Broken → Sharp	Handles collapse to zero.
Sharp → Smooth	New handles are auto-generated with the `initializeSplinePoint` algorithm, sized from the neighboring points. You can then drag them to refine the curve.
Sharp → Broken	Same auto-generated handles as Sharp → Smooth, but they start unlinked so you can move each independently.

Step 9

Round-trip a point through all three modes

Pick a Smooth point. Click Sharp → handles vanish. Click Broken → handles reappear (auto-sized) but unlinked. Click Smooth → they reconcile into a linked pair. Try this a few times to build muscle memory for what each transition does.

Outcome

You now understand the three point modes and how they shape your profile:

Smooth — flowing curves with linked Bézier handles, ideal for organic designs
Broken — corner with independent handle control on each side; the Illustrator-style "in-between"
Sharp — hard corners without handles, ideal for geometric and angular designs
Mixed — combine all three in one profile for maximum creative control

You also know the fast path into Broken: Alt + drag a handle on a Smooth point. No need to open the mode picker.

What's Next

Tutorial 4: Mastering Bézier Handles — Learn how to drag, adjust, and fine-tune the Bézier handles on Smooth and Broken points to create precisely shaped curves.