Renders what is inside a specified rectangular region within the viewport, and leaves
the remainder of the viewport as displayed.

Use this command when you need to render part of the model for testing settings and
effects.

The following prompts are displayed.

Pick crop window to render (first point)

Select the first corner of the region you want to render.

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.