Merge 3D Node

In Fusion, each 3D node (Shape 3D, Camera 3D, Point Light, …) produces an isolated 3D scene stream. As long as they don't go through a Merge 3D, they coexist but don't interact with each other. Merge 3D combines these streams into a single environment where everything sees and affects everything else.

It is the node you add most often to a 3D graph. A simple 3D comp almost always looks like this:

Shape 3D ──┐
Camera 3D ─┼─→ Merge 3D ──→ Renderer 3D ──→ (2D)
Light 3D ──┘

• Effects Library: Tools > 3D > Merge 3D
• Quick add: right-click in the Node Editor → Add Tool > 3D > Merge 3D
• In the toolbar, the Merge 3D icon (a cube with circles) is in the 3D section.

Four things to remember:

1. Every 3D element must go through a Merge before reaching a Renderer 3D. Otherwise, the renderer doesn't "see" the scene.
2. The camera must be in the same Merge as the objects to render them. If you have a Fog 3D or a Locator 3D that needs "a camera", it looks for it in the scene coming through its input - so in the previous Merge.
3. The Merge's transforms apply to all its children - moving the Merge moves the whole scene inside it. This is Fusion's native parenting mechanism.
4. No limit on the number of inputs - the node automatically adds inputs as you connect to it.

Merge 3D has a dynamic multi-input architecture: unlike standard nodes with a fixed number of inputs, Merge 3D automatically creates a new input as soon as you connect something, always keeping at least one free input visible.

• SceneInput (multicolor) - accepts any 3D stream: Shape 3D, Image Plane 3D, Camera 3D, lights, FBX Mesh 3D, another Merge 3D, and so on.
• Order doesn't matter - the inputs are processed in parallel. There is no notion of "foreground / background" as in a 2D Merge.
• No theoretical limit on the number of connections. In practice, beyond 15-20 inputs on a single Merge, chain several Merges instead to keep the graph readable.

Pass Through Lights (default: off)

The only checkbox in the Controls tab. On: the Merge's lights are "passed on" to downstream Merges and can light other objects added further along. Off (default): the lights stay confined to their current Merge. See the dedicated section.

The other parameters visible in the Inspector come from the Transform and Settings tabs, shared by all 3D nodes.

By default, lights connected to a Merge 3D only light the objects in that same Merge. If you chain several Merges to add more geometry downstream, those new objects won't be lit by the lights of the first Merge.

Turn on Pass Through Lights when you want the light to travel through the whole pipeline. Typical cases:

• A global lighting setup in a "master" Merge, then several child Merges that add detail objects.
• An environmental HDR Light you want to apply to all future geometry.

Keep it off if you want to isolate a particular lighting setup instead (for example two side-by-side scenes with their own lights, combined later through a new Merge).

You can (and often should) chain several Merge 3D nodes for organization and control. Examples:

Organizing by "logical group"

Merge 3D "Props"      ──┐
Merge 3D "Characters" ──┤
Merge 3D "Environment"──┼→ Merge 3D "Final" → Renderer 3D
Camera 3D             ──┤
Lights                ──┘

Each sub-scene stays readable, and you can apply a global transform on the Final Merge to move everything as a block (e.g. shift the whole scene 10 units in Y).

Hierarchical parenting

Plugging Merge 3D A into Merge 3D B makes A inherit B's transforms. This is the parenting mechanism. To rotate a group of objects around a shared axis, put them in a Merge 3D and animate that Merge's rotation.

The Transform tab applies a global transform (Translation, Rotation, Scale, Pivot) to everything inside the Merge. It is the same as inserting a Transform 3D right after the Merge - but built into the same node, so a bit cleaner for simple animations.

• Translation X/Y/Z - in Fusion units
• Rotation X/Y/Z - in degrees, with an order menu (XYZ, YXZ, ZXY, …)
• Scale X/Y/Z - default 1.0; Uniform Scale links the three axes.
• Pivot - center of rotation / scale.

1. Minimal 3D comp

Shape 3D → Merge 3D ← Camera 3D → Renderer 3D → Saver

One object, one camera, one render. Zero lights = ambient render (constant neutral lighting).

2. Scene lit with several lights

Shape 3D       ──┐
Directional Light┤
Point Light    ──┼→ Merge 3D → Renderer 3D
Camera 3D      ──┘

The lights and the object are in the same Merge → the light "sees" the object.

3. Two side-by-side scenes

Scene A (objects + lights) → Merge 3D A
Scene B (objects + lights) → Merge 3D B

Merge 3D A ──┐
Merge 3D B ──┼→ Merge 3D Final → Renderer 3D
Camera 3D  ──┘

Independent scenes combined at the end. If you want A's lights to light B as well, turn on Pass Through Lights on Merge A.

4. Animated group

Put the objects of an "articulated arm" in a dedicated Merge 3D, then animate the Merge's rotation → the whole arm rotates together around the chosen pivot. The equivalent of a hierarchical parent in Maya.

• If nothing shows up in the renderer - very often the final Merge is missing a camera, or the camera isn't connected to the right Merge.
• Light that doesn't work - check that it is in the same Merge as the object it should light. If it comes from an earlier Merge, turn on Pass Through Lights.
• Input order doesn't matter - unlike a 2D Merge where input order changes the compositing, here the order has no effect on the render.
• Lots of inputs = hard to read - beyond 10 inputs, chain several Merges to group elements logically (props, characters, environment, fx).
• To move a whole scene, use the Merge's Transform tab rather than adding a Transform 3D after it - fewer nodes.
• Name your Merges (e.g. Merge3D_Characters) if your comp has several - Fusion names them Merge3D1, Merge3D2… which quickly makes the graph unreadable.

The Settings tab has the options shared by 3D nodes (visibility, object ID, common render settings).