Graphics configuration and fine-tuning

This article provides guidance for the Linux VDA graphics configuration and fine-tuning.

For more information, see System requirements and the Installation overview section.

Configuration

Video codec for compression

Thinwire is the display remoting technology used in the Linux VDA. The technology allows graphics generated on one machine to be transmitted, typically across a network, to another machine for display.

The Use video codec for compression graphics policy sets the default graphics mode and provides the following options for different use cases:

• Use when preferred. This setting is the default. No additional configuration is required. It ensures that Thinwire is selected for all Citrix connections, and optimized for scalability, bandwidth, and superior image quality for typical desktop workloads.
• For the entire screen. Delivers Thinwire with full-screen H.264 or H.265 to optimize for improved user experience and bandwidth, especially in cases with heavy use of 3D graphics.

• For actively changing regions. The adaptive display technology in Thinwire identifies moving images (video, 3D in motion). It uses H.264 only in the part of the screen where the image is moving. The selective use of the H.264 video codec enables HDX Thinwire to detect and encode parts of the screen that are frequently updated using the H.264 video codec. Still image compression (JPEG, RLE) and bitmap caching continue to be used for the rest of the screen, including text and photographic imagery. Users get the benefit of lower bandwidth consumption and better quality for video content combined with lossless text or high quality imagery elsewhere. To enable this feature, set the Use video codec for compression policy to Use when preferred (default) or For actively changing regions. For more information, see Graphics policy settings. To enable H.264 hardware encoding for this feature, see H.264 hardware encoding.

  

Some other policy settings, including the following visual display policy settings can be used to fine-tune the performance of display remoting:

• Preferred color depth for simple graphics
• Target frame rate
• Visual quality

H.264 hardware encoding

The Use hardware encoding for video codec policy allows the use of graphics hardware, if available, to compress screen elements with the video codec. If such hardware is not available, the VDA falls back to CPU-based encoding using the software video codec.

Starting with version 2204, the Linux VDA supports selective use of the H.264 hardware codec for actively changing regions. This feature offloads CPU video compression consumption to hardware and improves image quality and the number of frames per second (FPS). To enable the feature, do the following:

1. Enable the Use hardware encoding for video codec policy.

2. Enable the Use video codec for compression policy and select For actively changing regions.

Allow visually lossless compression

The Allow visually lossless compression policy allows visually lossless compression to be used instead of true lossless compression for graphics. Visually lossless improves performance over true lossless, but has minor loss that is unnoticeable by sight. This setting changes the way the values of the Visual quality setting are used.

The Allow visually lossless compression policy is disabled by default. To enable visually lossless compression, set Allow visually lossless compression to Enabled and the Visual quality policy to Build to Lossless.

If the Use video codec for compression policy is set to Do not use video codec, visually lossless compression applies to static image encoding. If the Use video codec for compression policy is set to a graphics mode other than Do not use video codec, visually lossless compression applies to H.264 encoding.

The following clients support Selective H.264:

• Citrix Receiver for Windows 4.9 through 4.12
• Citrix Receiver for Linux 13.5 through 13.10
• Citrix Workspace app 1808 for Windows and later
• Citrix Workspace app 1808 for Linux and later

For more information about the Visual quality and Use video codec for compression policy settings, see Visual display policy settings and Graphics policy settings.

Support for H.265 video codec

Starting with the 7.18 release, the Linux VDA supports the H.265 video codec for hardware acceleration of remote graphics and videos.

You can use this feature on:

• Citrix Receiver for Windows 4.10 through 4.12
• Citrix Workspace app 1808 for Windows and later

To benefit from this feature, enable it on both the Linux VDA and on your client. If the GPU of your client doesn’t support H.265 decoding using the DXVA interface, the H.265 Decoding for graphics policy setting is ignored and sessions fall back to using the H.264 video codec. For more information, see H.265 video encoding.

To enable H.265 hardware encoding on the VDA:

1. Enable the Use hardware encoding for video codec policy.
2. Enable the Optimize for 3D graphics workload policy
3. Ensure that the Use video codec for compression policy is default or set to For the entire screen.
4. Ensure that the Visual quality policy is NOT set to Build to Lossless or Always Lossless.

To enable H.265 hardware encoding on your client, see H.265 video encoding.

Support for YUV444 software encoding

The Linux VDA supports YUV444 software encoding. The YUV encoding scheme assigns both brightness and color values to each pixel. In YUV, ‘Y’ represents the brightness or ‘luma’ value, and ‘UV’ represents the color or ‘chroma’ values. You can use this feature on Citrix Receiver for Windows 4.10 through 4.12 and on Citrix Workspace app 1808 for Windows and later.

Each unique Y, U, or V value comprises 8 bits, or one byte, of data. The YUV444 data format transmits 24 bits per pixel. The YUV422 data format shares U and V values between two pixels, which results in an average transmission rate of 16 bits per pixel. The following table shows an intuitive comparison between YUV444 and YUV420.

YUV444	YUV420

To enable YUV444 software encoding on the VDA:

1. Enable the Allow visually lossless compression policy.
2. Ensure that the Use video codec for compression policy is set to For the entire screen.
3. Ensure that the Visual quality policy is set to Always Lossless or Build to Lossless.

Graphics quality slider

We have included a graphics quality slider in the graphics status indicator tool that runs in your virtual Linux sessions. The slider helps to find the right balance between image quality and interactivity.

To use the slider, complete the following steps:

1. Enable the Graphic status indicator policy in Citrix Studio.

   

2. Open the Terminal and run the ctxslider command. The slider UI appears.

   Note:

   If you have set the Visual Quality policy to Always Lossless or Build to Lossless, the slider UI is not showing.

   

   The following choices are now available:

   • To change the image quality, move the slider. The slider supports a range of 0–9.
   • To use system-defined settings, select Let the system decide.
   • To switch to lossless mode, select Pixel perfect.

Adjust average bit rates based on bandwidth estimates

Citrix enhances HDX 3D Pro hardware encoding by adjusting average bit rates based on bandwidth estimates.

When HDX 3D Pro hardware encoding is in use, the VDA can intermittently estimate the bandwidth of the network and adjust the bit rates of encoded frames accordingly. This new feature provides a mechanism to balance between sharpness and fluency.

This feature is enabled by default. To disable it, run the following command:

sudo /opt/Citrix/VDA/bin/ctxreg create -k "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Citrix\Thinwire" -t "REG_DWORD" -v "DisableReconfigureEncoder" -d "0x00000001" --force
<!--NeedCopy-->