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Tutorial 4: Mastering Bézier Handles

Bézier handles are the secret to shaping truly beautiful curves. In this tutorial you will learn exactly how to drag, adjust, and control the tangent handles on Smooth and Broken control points — including the precision and tangency-breaking gestures borrowed from Illustrator and Figma.

What you'll learn

Prerequisites

Step 1: Identify the two handles

Step 1

Select a Smooth point

Click an interior control point that is in Smooth mode. Two small dots appear, connected to the point by thin lines:
- Incoming handle (colored amber/warm) — controls how the curve arrives at this point from below.
- Outgoing handle (colored green) — controls how the curve leaves this point toward the next point above.

Each handle is a small vector that defines the tangent direction and strength of the curve at that control point. Longer handles create broader, lazier curves. Shorter handles create tighter bends.

Step 2: Drag the outgoing handle

Step 2

Pull the green handle outward

Click and drag the green (outgoing) handle dot. Pull it to the right — the curve above the point bulges outward. Pull it to the left — the curve tucks inward. Pull it upward — the curve rises steeply. Pull it downward — the curve stays flatter near the point before rising.

As you drag, notice that the incoming handle on the opposite side mirrors your movement. This keeps the curve smooth through the point. If you pull the outgoing handle right, the incoming handle pulls left by the same amount, maintaining tangent continuity.

Step 3: Drag the incoming handle

Step 3

Pull the amber handle

Now click and drag the amber (incoming) handle dot. The curve below the point changes shape. Again, the opposite handle mirrors the direction to maintain smoothness.

Step 4: Hold Shift for fine control

When you are zeroed in on the perfect curvature and even one pixel of mouse movement is too coarse, hold Shift as you drag.

Step 4

Shift + drag for precision

Start dragging a handle. Press and hold Shift mid-drag. The cursor delta is now scaled to 10% — every 10 pixels of mouse movement equals 1 pixel of handle movement. Release Shift and the handle smoothly re-syncs to the cursor; there is no jump back to its old position.

This works on points and handles, in both the side-panel canvas and the in-viewport overlay. Use it whenever you need to land on an exact value or fine-tune a handle without disturbing the rest of the shape.

Step 5: Break tangency with Alt + drag

So far the opposite handle has always mirrored your drag direction — that is what Smooth mode is for. But sometimes you want a corner at the point with independent tangent control on each side. Hold Alt while dragging.

Step 5

Alt + drag a handle to break tangency

Pick a Smooth point. Hold Alt and drag one of its handles. Two things happen:
1. Only the dragged handle moves — the opposite handle stays put.
2. The point automatically promotes to Broken mode. You'll see the link lines render dashed and a small chevron marker appear on the anchor.

Once the point is Broken, you no longer need to hold Alt to move the handles independently — Alt only matters on the first drag that breaks the tangency. From that moment on you have full G0 control.

To get back to a linked Smooth point, click the Smooth button in the mode picker. The handle directions average onto a common tangent line again, but each side's length is preserved so you don't lose your curvature work.

Step 6: Control handle length for curvature strength

Handle length controls how "strongly" the curve follows that tangent direction:

Step 6

Compare long vs short handles

  1. Drag a handle far away from the point — the curve sweeps broadly in that direction, like a gentle hill.

Think of it like steering a car: a long handle means the curve "commits" to that direction for a long distance before turning. A short handle means it turns quickly.

Step 7: Edit handles directly on the 3D model

You don't have to use the side-panel canvas for everything. While the Create or Effects tab is open, an in-viewport overlay is automatically active — the same anchors and handles, projected onto the camera-facing meridian of the model.

Step 7

Drag a handle on the model itself

Move your cursor over the 3D viewer. Find the same anchor + handle dots overlaid on the silhouette of the model. Drag any of them — the side-panel canvas updates in lock-step. Both editors are always in sync because they edit the same data.

All the same gestures work in the overlay:

Step 8: Create a classic S-curve

The most iconic vase shape is an S-curve — a sinusoidal profile that goes from narrow to wide to narrow.

Step 8

Shape an S-curve

Set up three Smooth points:
1. Bottom — radius 20 mm
2. Middle (50% height) — radius 40 mm
3. Top — radius 15 mm

Now adjust handles on the middle point:
- Pull the incoming handle (amber) slightly to the left and downward — the curve rises steeply from the base and then flattens as it approaches the widest point.
- Pull the outgoing handle (green) slightly to the left and upward — the curve narrows smoothly toward the rim.

The 3D viewport shows a smooth, bulbous vase that tapers at both ends.

Step 9: Create a shoulder with handle asymmetry

Step 9

Build a bottle shoulder

Add 4 points:
1. Bottom — radius 30 mm
2. Point at 60% — radius 30 mm (same radius, creating a cylinder section)
3. Point at 75% — radius 15 mm (narrow neck)
4. Top — radius 18 mm (slight flare for the rim)

On the point at 60%, pull the outgoing handle far upward and slightly inward — this creates a smooth, gradual shoulder transition. Keep the incoming handle short to maintain the straight cylinder below.

On the point at 75%, keep handles short so the neck is tight and well-defined.

This technique creates the classic bottle shape: straight sides, smooth shoulder, narrow neck, and flared lip.

Step 10: Asymmetric shoulder with Broken mode

A shoulder transition where the lower side is curved but the upper side is straight is impossible with a Smooth point — the linked handles force symmetry of direction. Broken mode is built for exactly this.

Step 10

One side curved, one side straight

Take the previous bottle profile and select the point at 60%. Alt + drag the outgoing handle all the way down to collapse it (or as short as you can comfortably drag). The point promotes to Broken; the incoming handle keeps its long curve, while the outgoing side becomes a straight line up to the neck. You now have a smooth curved approach into a hard cylinder above — impossible to express with Smooth or Sharp alone.

Step 11: Use the profile table for precise handle values

Step 11

Check the Profile Points table

Look at the Profile Points table below the canvas. Each row shows:
- ⌀ mm — the diameter at that point (2 × radius)
- Height mm — the actual height in millimeters
- Layer — which layer number this height corresponds to (based on your layer height setting)

While you cannot edit handle positions numerically in the table, the dimensional readout helps you verify exact sizes as you drag handles on the canvas.

Step 12: Understand the height monotonicity rule

Step 12

What happens with extreme handles

Try dragging a handle so far that the curve loops backward in height (going down before going up again). The engine detects this non-monotonic height situation and automatically falls back to a safe evaluation mode that keeps the curve printable.

Outcome

You now have full control over Bézier handles in both editors:

What's Next

Tutorial 5: Using Shape Presets — Learn how to load built-in profile presets as starting points and customize them for your designs.