Reaction Concepts
The following terms and concepts are used when working in Reaction.
An object is any element in a 3D scene. Lights, cameras, and surfaces are typically referred to as objects when working in Reaction.
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.
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.
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.
A surface is a geometric object onto which a source is mapped to create a layer for your composition. Available geometric types are bilinear, frustum, box, plane, and sphere. Each surface has a local axis that you can use to transform the layer—see Working with Geometric Surfaces.
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.
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.
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.
Shaders are programs that help define the look of objects in your scene. They can be considered a part of the rendering pipeline.