Graphics Administration Guide (April 2009)

performing buffer swaps on vertical blank
For performance reasons, the default DBE behavior is to not synchronize buffer swaps with the
monitor’s vertical retrace period. In some instances, therefore, image tearing (seeing part of the
old image and part of the new image on the display at the same time) could be visible while
swapping large DBE windows. For those instances where tearing would occur and is undesirable,
an optional X Server mode is available to allow for synchronization of buffer swaps with vertical
retrace. To activate this optional X Server mode, set the following screen option in the X*screens
File before the X Server is started:
SwapBuffersOnVBlank
determining swap performance
The DBE API does not allow users to determine if double-buffering in a visual is through software
or hardware. However, the API does provide a way to determine relative swapping performance
on a per-visual basis. The XdbeScreenVisualInfo() function returns information about the swapping
performance levels for the double-buffering visuals on a display. A visual with a higher
performance level is likely to have better double-buffer graphics performance than a visual with
a lower performance level. Nothing can be deduced from any of the following: the magnitude
of the difference of two performance levels, a performance level in isolation, or comparing
performance levels from different servers.
For more information, refer to the DBE man page on XdbeScreenVisualInfo().
display power management signaling (DPMS)
Monitors constitute a large percentage of the power used by a workstation even when not actively
in use (i.e., during screen blanking). In order to reduce the power consumption, the Video
Electronic Standards Association (VESA) has defined a Display Power Management Signaling
(DPMS) standard which can be used to greatly reduce the amount of power being used by a
monitor during screen blanking.
The following table is a description of the states that are defined by VESA. The Power Savings
column indicates (roughly) the level of power savings achieved in the given state. The Recovery
Time is the amount of time that the screen takes to return to a usable state when the screen saver
is turned off (by pressing a key or the moving the mouse).
Table 3-1 Power saving states defined by VESA
Recovery TimePower SavingsStateLevel
NoneNoneOn0
ShortMinimalStand-by1
LongerSubstantialSuspend2
System DependentMaximumOff3
The actual amount of power saved and the recovery time for each of the states is
monitor-dependent and may vary widely. The customer can compensate for this by choosing
an appropriate level for the monitor that is currently in use.
By default, the DPMS level used is the 0 or On (no power savings).
DPMS should not be confused with screen blanking or screen saving. Screen blanking will merely
cause the screen to go dark. Screen saving will display a changing pattern on the screen to avoid
the burn-in of a static image. Neither of these will cause any power saving to occur.
shared memory extension (MIT_SHM)
The MIT shared memory extension provides both shared-memory XImages and shared-memory
pixmaps based on the SYSV shared memory primitives.
36 configuring X server on HP-UX (HP Visualize-FXE)