This article includes information about the display adapter selection process, how virtual monitors are created, and manual configuration options for the same.
Starting with XenDesktop 7.16 the Citrix Virtual Desktop Agent (VDA) for Windows 10 automatically selects the best display adapter to use for the user session during connection time. This feature eliminates the HDX 3D Pro mode installation option from previous versions and allows for the same Windows image to be used for virtual machines with and without GPUs alike.
There are three different display adapters (or drivers) that may be used in a Citrix session:

• Citrix Display Only (DOD) – This is the standard adapter used for all Citrix sessions when there is no GPU detected on the VDA.
• GPU Vendor’s – This may be one of the GPU adapters from NVIDIA, AMD, or Intel that Citrix supports for HDX 3D Pro workloads as documented in CTX131385.
• Citrix Indirect Display (IDD) – This adapter is used in sessions where a GPU is detected but no Citrix supported vendor driver is found. It can be considered as “generic” GPU support.

Instructions

Manual configuration
By default, the optimal configuration will be automatically selected in most cases. Manual configuration options should only be used as needed to support specific use cases, as instructed by Citrix Technical Support, or for troubleshooting and diagnostic purposes.

On VDAs version 7.16 and newer, administrators can pre-define how display adapters and monitors are configured for the user session using the following Windows Registry Key:

To select the preferred display adapter and assign usage priority (merits) for multiple display adapters

To restrict the number of monitors that can be created per display adapter

 
Configuration Example

 
With the registry settings illustrated above, the administrator has configured the Citrix Indirect Display adapter with highest preference followed by the Nvidia adapter and maximum number of monitors allowed for both to 1. In this example, the session will use the Citrix IDD adapter for the primary monitor and the NVIDIA adapter for the secondary monitor, for a user connecting from an endpoint with two monitors.

There may be cases where using the Citrix IDD adapter (generic GPU support) is preferred or required, over the GPU vendor’s. Mainly as a troubleshooting step or a workaround to issues with GPU vendor adapters. For these cases the registry key may be configured with the single value as follows:

Use Citrix IDD as a workaround to the following known issues: