Qt for Embedded Linux Display Management

Subdrivers and Multiple Drivers

The VNC, Transformed and Multi screen drivers depend on subdrivers. The general syntax for specifying a driver is as follows:

 export QWS_DISPLAY="<driver>[:<subdriver>][:<subdriver options>]...
         [ :<display num>]"

In the case of subdrivers, it is important to add a space between each subdriver and before the display number to separate the various drivers and displays. Note that Multi screen drivers can have several subdrivers. For example:

 export QWS_DISPLAY="Multi: QVFb:0 QVFb:offset=640,0:1 :2"

Note also that the VNC screen driver defaults to a virtual screen driver if no subdriver is specified. In this case the VNC driver accepts a few additional (optional) arguments specifying the size and depth of the default virtual screen:

• size=<width x height>
• depth=<value>
• mmHeight=<physical height in millimeters>
• mmWidth=<physical width in millimeters>

Example running the VNC screen driver with a virtual screen of size 720x480 with 32 bits per pixel:

 export QWS_DISPLAY="VNC:size=720x480:depth=32"

Example running the VNC screen driver on top of the Linux framebuffer driver:

 export QWS_DISPLAY="VNC:LinuxFb"

In this last example, Qt is using two screen drivers simultaneously, displaying output on both the device's screen and across a network on VNC client displays.