Before you composite or add effects to a composition in Reaction, you typically set the background. The background is the rendering plane for your composition and sets the format. If you connect a Reaction tool to an image or to a tool output in an existing dependency graph, the background is set automatically. You can change the background at any time.

To set the background automatically in the Layer Editor:

1. In the Tools tab, drag the Reaction tool to the Layer Editor.

   The composition drop gate appears. Depending on your dependency graph, you will see some or all of the following choices:

   

2. Decide where to add Reaction in your dependency graph.

   The background is set accordingly, and appears in the Layer Editor.

To set the background automatically in the Schematic view:

1. Drop the Reaction tool onto an existing tool or image output connection in the Schematic view.

To set the background manually in the Schematic view:

1. Connect a media or tool node output to the background input connector.

To set or replace the background using the drop gate:

1. Select the desired Reaction tool in the Schematic or Layer Editor.

   In the Schematic view, the Reaction tool is highlighted.

2. Select the composition to use as the background and drag it to the Schematic, Layer Editor, or Player.

   The Reaction drop gate appears.

3. Swipe through Set Background.