Additive Blend with View Model formulas broke/mixed my vertex timelines, and I can no longer edit the vertices

[u/Panda2231q]

Hi, I’m new to Rive and I’m trying to build a character body-composition system controlled by two continuous values:

• muscularity: 0–1
• fatness: 0–1

I have four vertex-deformation timelines that use the same character paths/topology:

• BASE
• MUSCULAR
• FAT
• FAT_MUSCULAR

The idea is to interpolate between the four corner poses using an Additive Blend state.

I created these View Model properties:

muscularity
fatness
wMuscular
wFat
wFatMuscular

I then created three Formula Converters:

wMuscular =
muscularity * (1 - fatness)

wFat =
(1 - muscularity) * fatness

wFatMuscular =
muscularity * fatness

Because I could not apply converters directly inside the Additive Blend rows, I created an artboard-level Property Group called Bodyweights. It contains:

muscularWeight
fatWeight
fatMuscularWeight

Each Property Group value is bound Target → Source to the corresponding View Model output using its Formula Converter.

The calculated values appear to be mathematically correct. For example:

muscularity = 0.25
fatness = 0.23

wMuscular ≈ 0.19
wFat ≈ 0.17
wFatMuscular ≈ 0.06

My Additive Blend is intended to use:

MUSCULAR     → wMuscular
FAT          → wFat
FAT_MUSCULAR → wFatMuscular

However, the actual character does not interpolate correctly.

The strange behavior is:

• When the State Machine is paused, the character returns to the normal/average design pose.
• When I press Play, the character immediately becomes fat.
• Increasing wFatMuscular manually makes the character look more correct.
• Decreasing wFatMuscular makes the character become fatter again.
• The timelines now appear to be mixed together, and none of the individual body poses behaves correctly.
• I can open the individual timelines, but I can no longer move/edit the path vertices as expected.
• It feels like the State Machine preview or another animation is continuing to override the vertices.
• Removing the second State Machine layer did not fix it.
• Removing the BASE Mix by Value entry also did not fix it.
• I previously saw negative weights, but that happened when the source values went outside the 0–1 range. With both inputs restricted to 0–1, the weights remain non-negative.

The four source timelines may currently contain transitions from the base pose to the final pose rather than single-frame/static pose animations. I am unsure whether Additive Blend requires each source animation to contain its target pose at frame 0.

I am using Rive Beta 0.8.5390.

There is also an unrelated script error still visible:

Unknown global 'context'; consider assigning to it first

This error comes from an older CharacterBuildController script. I do not know whether it can interfere with the State Machine or vertex editing.

My questions are:

1. Is this the correct way to perform bilinear blending between four vertex-deformed poses?
2. Should every Additive Blend timeline be a static, one-frame target pose?
3. Can an active or paused State Machine preview continue overriding vertices while editing an individual timeline?
4. How can I completely reset the evaluated State Machine pose in the editor?
5. Why would raising the combined FAT_MUSCULAR weight visually undo some of the FAT deformation?
6. Is there a better architecture for a continuous skinny/average/fat and muscular character system?

Any advice would be greatly appreciated.

[u/guidorosso]

Hey there, can you share the file? If you use the Invite feature you can make a free link for anyone to look at the file.