Renders a specified rectangular area, called a crop window, within a viewport.

Button
Ribbon: Render tab
Render
panel
Render
RegionNot available on the ribbon
in the current workspaceRenders what is inside a specified rectangular region within the viewport, and leaves the remainder of the render window intact.
Use this command when you need to render a part of the model for testing settings and effects.
The following prompts are displayed.
Pick crop window to render: Select the first corner of the region you want to render
Please enter the second point: Select the opposite corner of the region you want to render

The current render destination and rendering procedure is ignored. After the second corner of the render region is selected, the rendering task proceeds and displays a viewport rendering with cropping.