How to Combine Interpolated Mouth Swaps with Adjustable Mouth Shape Controls

Treat the rig as two cooperating systems. The Switch keys determine which base drawing appears and when it changes. Shape controls determine how that drawing is adjusted during animation.

For this workflow, use the following division of responsibility:

Control	Job	Where to animate it
Mouth Switch	Select closed, open or rounded artwork	Switch layer’s timeline
Horizontal layer scale	Adjust overall mouth width	Mouth Switch’s transform channels
Left and right corner bones	Adjust the mouth corners locally	Bones inside the Mouth Switch
Optional Smart Bone	Drive an authored deformation	Separate deformation action

Avoid putting the sequence of mouth selections inside a Smart Bone Action when you need freely chosen interpolated swaps. In a documented Moho workflow, a selection dial traverses its stored drawing sequence; Step keys remove the continuous transition. The author recommends the Switch Selection window for mouth selection. This limitation concerns a dial that selects drawings, rather than every possible use of Smart Bones. Make smart bone dial for switch layers

Begin with a deliberately simple mouth. At frame 0, create a Switch layer named Mouth, then add a child vector layer named Open. Draw a filled, closed loop with six control points: left corner, two upper points, right corner and two lower points.

Duplicate Open to create Closed and Round. Reshape the existing points in each duplicate. For Closed, bring the upper and lower edges close together. For Round, move the corners inward and adjust the upper and lower points to form a rounded opening.

Moho’s manual requires vector sublayers with equal control-point counts for the basic interpolation setup. The original Switch layers in Moho tutorial demonstrates duplicating a base mouth and modifying its points, which helps preserve corresponding structure. Switch Layers, Switch layers in Moho

Equal counts are only the starting check. Keep each point’s role consistent: the left corner should remain the left corner in every drawing. Do not redraw one variation independently or add detail to only one mouth. For this initial rig, leave additional interior artwork out until the outline transitions correctly.

Open the Mouth layer’s settings and enable Interpolate sub-layers. Create a short selection test on the main timeline using the Switch Selection window or the Switch layer’s context menu.

Use this illustrative sequence:

Frame	Selected mouth	Purpose
1	Closed	Starting pose
9	Open	Test vertical opening
17	Round	Test narrowing and rounding
25	Closed	Test the return transition

These frame numbers are a convenient test sequence, not prescribed animation timing. Scrub between the keys and inspect the intermediate silhouettes. The original tutorial explains that interpolation creates shapes between Switch keyframes and that its suitability depends on the artwork and animation style. Switch layers in Moho

Check frames between the endpoints before adding controls. Look for crossed outlines, unexpected twists and corners that travel across the opening. If an endpoint looks correct but its transition fails, compare the corresponding points in the two source drawings. Fix the base artwork before adding another deformation.

For a first adjustable control, place the Switch layer’s origin at the mouth’s center and animate its horizontal scale. This gives the entire mouth set a common width adjustment. A published Moho rigging discussion describes using parent Switch transforms for secondary squash and stretch after the mouth-selection pass. Which mouth shapes for accurate lip syncing

As an illustrative starting range, try horizontal scales of 0.9, 1.0 and 1.1, keeping vertical scale at 1.0. These values represent modest narrowing, the original width and modest widening; choose the final range by inspecting your artwork.

Test all three base mouths at each width. Judge the rounded mouth especially carefully: widening it may undermine the shape you selected. Reduce the adjustment wherever the silhouette stops serving its purpose.

Use width scaling for overall proportion. For a change that should affect only the corners, add local controls instead of increasing the scale adjustment.

Moho makes bone tools available on Switch layers. For this small rig, explicit point binding provides a clear way to assign each mouth corner to its own control. The official binding tutorial documents selecting a bone, selecting vector points and pressing Space to bind them. It also explains that manual binding can produce abrupt deformation where differently bound regions meet. Bone Tools, Tutorial 3.1: Bone binding

At frame 0, use this setup:

1. Select Mouth and create three bones: MouthCenter, CornerL and CornerR. Make both corner bones children of MouthCenter.
2. Select the Open vector layer. Select MouthCenter, activate Bind Points, select all six points and press Space.
3. Select CornerL, select only the left corner point and press Space to reassign it.
4. Repeat for the right corner using CornerR.
5. Apply the same assignments to Closed and Round. Every corresponding corner must follow the same bone.

Move to an animation frame after frame 0 and translate the corner bones slightly. Keep the movements small at first. Moho distinguishes setup from animation: repositioning bones at frame 0 changes their layout, while movement at later frames animates bound artwork. Bone Tools

Check the closed mouth after each adjustment. Raising both corner points can open unwanted gaps or create sharp bends. If that happens, reduce the movement or redesign the outline’s point placement. A six-point mouth is a useful starting rig; more elaborate artwork may need smoother binding or a deformation mesh.

Once the basic rig works, a Smart Bone can provide a reusable authored shape adjustment. Moho’s current feature documentation describes Smart Bones as control levers connected to actions that animate facial expressions and other elements. Moho Features

For a shared deformation across more elaborate mouth artwork, consider the documented mesh approach. In an original technical account, D. R. Greenlaw describes placing the master mesh outside the Switch, adding a reference copy inside each mouth group, giving each reference a unique name and assigning the artwork to its appropriate mesh reference. A Smart Bone animates the master mesh. Switch layer interpolation with mesh warp image layers — Page 3

That is an advanced alternative to the simple direct-vector setup above. It changes the layer structure and requires testing the mesh assignment in every mouth group. Use it when controlling selected outline artwork independently is worth the added setup.

The same author’s later workflow keeps mouth selection on the main timeline and applies the separate deformation dial afterward. This supports the central design choice: preserve independent access to the base mouths while adjusting their appearance. interpolate sub-layers in the action

Use a small combination test to find problems that isolated controls miss. This test matrix is a practical diagnostic derived from the separate selection-and-deformation workflow; it is not a reported product benchmark.

Test	What to inspect	First adjustment to try
Each mouth at neutral controls	Base silhouette	Correct the source drawing
Each mouth at narrow and wide settings	Shape remains recognizable	Reduce width range
Closed mouth with raised corners	Closure and smooth curvature	Reduce corner travel
Open-to-round transition with controls held	Stable intermediate shapes	Check point correspondence and binding
Controls moving during a swap	Continuous outline movement	Test each control separately
Rendered test sequence	Appearance matches the intended result	Inspect the affected frame and layers

Animate in passes: first mouth selection, then width and corner movement, then any additional deformation. When a problem appears, return the shape controls to neutral. If the transition still fails, investigate the drawings and Switch setup. If it works at neutral, isolate the width adjustment, corner binding or mesh deformation.

Your finished rig should let you change mouth timing without rebuilding its adjustable controls. Keep the base mouths compatible, give each control a clear purpose and inspect combinations between keyframes. That provides a practical foundation for smooth mouth swaps with editable shapes.

• Switch Layers — Lost Marble official manual.
• Moho Features — Lost Marble official product documentation.
• Switch layers in Moho — Original illustrated tutorial.
• Make smart bone dial for switch layers — Original technical discussion.
• Which mouth shapes for accurate lip syncing — Original rigging discussion.
• Bone Tools — Lost Marble official manual.
• Tutorial 3.1: Bone binding — Lost Marble official tutorial.
• Switch layer interpolation with mesh warp image layers — Page 3 — Original mesh workflow account.
• interpolate sub-layers in the action — Original discussion of separate selection and deformation controls.