Reaction Tool

The Reaction super tool provides a complete multilayer compositing and 3D effects environment. You can use Reaction to quickly composite and output numerous images that are already processed using other tools, as well as cross over into a 3D environment where you can apply lighting, spatial, visualization, and rendering effects to your scene. You can then use your Reaction output to render your final composition, or use it as an input to other tools in your dependency graph, including another Reaction.

A Reaction tool is considered a “super tool” because it contains a set of tools that you can use to create 3D compositing effects on your composition. All individual tools contained in Reaction can be accessed by opening the Group Schematic. Reaction is used like any other tool, but can also be used in tandem with the Layer Editor to build and edit compositions interactively.

You can use as little or as much of the available functionality as needed to get your job done. You may want to simply create a few layers where one layer is repositioned to place a character in a scene, or create a 3D scene with lighting and texture effects. Regardless, the Reaction tool behaves like any other tool in Composite; you can delete and connect a Reaction tool to other output nodes in the same manner.

Whether you want to quickly perform straightforward 2D compositing or create 3D effects, the first thing you'll do is set your composition background to define the rendering plane, then you'll create layers in Reaction.

The following terms and concepts are used when working in Reaction.

Object

An object is any element in a 3D scene. Lights, cameras, and surfaces are typically referred to as objects when working in Reaction.

Source

A source is an input node to the Reaction tool. You can assign a source composition or image generator to a layer in your composition, or use the source as an input to a texture channel in a material node or image channel in a light node. When you add a Reaction tool to your dependency graph, its initial input is designated as the background for your composition. You can then add as many source nodes and layers to the Reaction tool as needed.

Layer

When performing multilayer compositing using Reaction, you typically set a background, although you are not required to, then assign source inputs to layers. A layer is composed of three separate components: a surface (3D geometry) object and local axis, a multi-channel material object, and a layer element. When viewing the Reaction node in the Group Schematic, you can see each component—see Working with Layers.

Material

A material defines how a layer interacts with lights to define how a scene is rendered. Each layer must have a material associated with it, but many layers can share a single material—see Working with Materials.

Surface

A surface is a geometric object onto which a source is mapped to create a layer for your composition. Available geometric types are bicubic, bilinear, frustum, box, geometry, plane, and sphere. Each surface has a local axis that you can use to transform the layer—see Working with Geometric Surfaces.

Camera

Each Reaction node includes a camera for viewing and rendering the scene. By default, the camera is set to perspective, and positioned, so that you can view your layers in 2D and immediately perform standard multilayer compositing, although you may want to set the camera to orthographic. You can add several cameras to a scene, but you can only choose one to render, called the render camera—see Working with Cameras.

Axis

Each layer has its own axis, or center, that you can use to perform transformations locally. You can also add axes to your scene to apply transformations to several objects at once, or to create more complex transformation effects. When you add an axis object to a Reaction tool, you can then parent it to one or more objects or layers—see Using Parenting Axes.

Light

Lights are used to illuminate your scene and apply lighting effects to surfaces. You can choose omni, directional, or spotlights and set lighting color, intensity, and decay, as well as create shadows and apply transformations to the light itself. Lights also have a Projector Image channel that you can connect to a source to project an illuminated image onto a layer or the scene—see Working with Lights.

Shader

Shaders are programs that help define the look of objects in your scene. They can be considered a part of the rendering pipeline.

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