Virtualisation d'applications

ClearType…

Par Laurent Falguière ⋅ 5 September 2008 ⋅  Envoyer cet article ⋅  Imprimer cet article ⋅

Evaluer cet article:

 Loading ...

Cleartype is a subpixel rendering technology based on anti-aliasing first introduced by Microsoft in Windows XP (turned on by default starting with Internet Explorer 7). The following example shows the font smoothing rendered using Cleartype:

Originally, ClearType was supported neither over RDP nor over ICA… Since Office 2007 and Windows Vista have Cleartype turned on by default and with the increasing number or LCD monitors, Microsoft has worked on implementing ClearType over RDP.

How to turn on/turn off ClearType?

Remote Desktop Connection Client

The “Font Smoothing” checkbox has been introduced starting with RDC client version 6 (turned off by default). This checkbox is available in the “Advanced” tab of the Remote Desktop Connnection Client.

Terminal Server 2008

Windows 2008 supports natively ClearType over RDP. You can enable this feature (on a per-user basis) using Control Panel (Appearance and Themes / Display / Appearance tab / Effects):

You can also configure ClearType using Registry (on a per-user basis):

HKEY_CURRENT_USER\Control Panel\Desktop\FontSmoothingType

0 - Font Smoothing disabled
1 - Standard Font Smoothing (for CRT monitors)
2 (default):  ClearType Font Smoothing (for LCD Monitors)

The “Font Smoothing” checkbox in the remote Desktop Connection need to be checked (not checked by default).

Terminal Server 2003

Windows 2003 doesn’t support natively Cleartype over Terminal Server, but Microsoft recently released an hotfix to support this font smoothing feature (KB946633). This hotfix requires Windows 2003 Service pack 1 or Service pack 1.

Once installed, you can disable Cleartype using Registry:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\TSEnableFontSmoothing

0 - Font Smoothing disabled
1 - Font smoothing enabled

Citrix Presentation Server 4.x

Windows font smoothing has been supported by Citrix for years: for instance, the Windows 2000 Server font smoothing feature (the “Smooth edges of screen fonts” checkbox in the Display Properties dialog box) was supported in ICA sessions with Metaframe… 

Since Windows 2003 doesn’t support font smoothing until KB946633 was released , there was no font smoothing support available in Citrix presentation Server. Citrix has released an hotfix (PSE450R02W2K3037) to support cleartype over  ICA in Presentation Server 4.5 (this hotfix requires the KB946633 Microsoft hotfix)…

Citrix XenApp 5.0

XenApp 5.0 supports Cleartype (natively  on Windows 2008 and with the Microsoft KB946633  hotfix on Windows 2003). You can manage font smoothing options using display properties or registry, as mentionned before, but also in the Web Interface site configuration options (Manage session preferences / Display / Allow font smoothing -checked by default-)

To provide End-users with the same application look for published and local applications, the behaviour has been modified starting with ICA client version 11. When used with XenApp for Windows 2008, the ICA client 11 reads font smoothing settings from client (in user profile)  instead of from the  XenApp server (in user profile). With previous clients (or non Windows clients), font smoothing setting are read from the XenApp server user profile…

Impact of ClearType on Bandwidth Usage

Using ClearType over RDP dramatically increases the bandwidth usage: “Performance Tuning Guidelines for Windows Server 2008” states “[Cleartype] does affect network bandwidth consumption significantly (generally more than 400 percent)”. Helge Klein de Sepago has tested Cleartype over RDP and his results are the same (+335% with 16bits color depth and  660% with 32bits color depth). He also gives an explanation: When Cleartype is enabled, the glyph caching mechanism is disabled (glyphs are bitmap representations of characters and the RDP protocol contains optimizations that minimize the number of times these glyphs need to be transferred over the network by caching them client side) and characters are transferred as bitmaps. Concerning the ICA protocole, Citrix announces that the bandwidth overhead when using ClearType is only 3%, but the CPU usage increases sensibly…

• http://www.microsoft.com/typography/ClearTypeInfo.mspx
• http://citrixblogger.org/2008/03/23/cleartype-and-terminal-services/
• http://blogs.sepago.de/helge/2007/08/03/windows-server-2008-architectural-changes-relevant-to-terminal-services-2/
• http://blogs.msdn.com/ts/archive/2006/09/08/747023.aspx
• http://blogs.sepago.de/helge/2008/07/16/how-to-configure-font-smoothing-on-presentation-server-and-xenapp/
• http://community.citrix.com/blogs/citrite/gusp/2008/07/16/How+to+Configure+ClearType+on+XenApp
• http://blogs.sepago.de/helge/2007/08/19/bandwidth-requirements-for-cleartype-over-rdp/
• Performance Tuning Guidelines for Windows Server 2008

Articles relatifs

• Terminal Server 2008: L'authentification au niveau réseau (0)
• Terminal Server 2008: Le mode vidage (drain mode) (0)
• Les licences Terminal Server (1ère partie) (14)
• Webcasts Terminal Server 2008 (0)
• Terminal Server Easy Print (1)