Creating an HDRI Environment

The most common use for the Render Tree Usage shader is to create a background that is visible from any camera angle at any distance and reflected on the surfaces of objects in your scene. Alternately, you can create a specific environment for a single object to speed up rendering.

Creating a Global Environment

To give a scene an environment map

Select the pass for which you want to generate the background environment and open its Render Pass Property Editor [Properties Reference].
Click the Pass Shaders tab.
In the Environment stack window, click Add to select the Render Tree Usage shader and click OK — it appears in the shader stack list.
Select the shader from the stack window and click Inspect.
From the Environment shader's property editor, select an HDR image clip to use as an environment map. Click the New button to create a new clip from file or from an existing image source.

Creating Local Environment

To give an object an environment map

Select the object to which you want to apply an environment shader. Make sure that you have applied a material to it.
From the Render toolbar, choose Get Shader Environment Environment Map — it is connected to the environment input of the selected object's material node. You can also make this connection using The Render Tree.
From the Environment shader's property editor, select an HDR image clip to use as an environment map. Click the New button to create a new clip from file or from an existing image source.

Setting Environment Shader Properties

From the Environment Mode list, choose the appropriate mode for mapping the image:
- Spherical maps the image spherically around the scene.
- Cylindrical maps the image cylindrically around the scene.
- Cubic Strip takes an image in which the faces of a cube are laid out horizontally, side by side, and maps it in a cubic shape around the scene.
- Cube Cross takes an image in which a cube has been unfolded to look like a cross and maps it in a cubic shape around the scene.
- Cube Cross Sideways is a cubic cross, but rotated 90 degrees.
Adjust the Background parameter to control the degree to which the image appears as the scene's background.
Adjust the Reflections parameter to control the intensity of the reflected environment map. Higher values create brighter reflections.
Adjust the Image parameter to control the intensity of final gathering lighting.
Adjust the Transformation settings, if necessary, to transform the environment map image.

Setting Renderer Properties

Open the mental ray Render Options Property Editor for the pass you want to render with the environment.
Click the Final Gathering tab, and select Enable.
Make sure to copy these settings to the active render region to preview final gathering in the render region (choose Render > Regions > Region Copy > Current Pass to Active Viewport).