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To obtain hardware double-buffering, find a visual in the image planes. The best method is to find all the
depth-8 PseudoColor visuals returned by XGetVisualInfo and then eliminate the visuals that are reported
in the SERVER_OVERLAY_VISUALS property (discussed below).
If you have an application that assumes the default visual has fast double-buffering, specify an image
plane visual as the default.
HCRX Overlay Visuals and Overlay Transparency
As on the CRX-24[Z] and CRX-48Z, a property on the root window, SERVER_OVERLAY_VISUALS,
is used to describe the visuals that are in the overlay planes.
Overlay Transparency on the HCRX-8[Z], HP [Dual] VISUALIZE-EG and HP
VISUALIZE-8
The HCRX-8[Z], HP [Dual] VISUALIZE-EG and HP VISUALIZE-8 each have one visual in the
overlay planes (depth-8 PseudoColor). By default, this overlay visual has no transparent index available
to applications for rendering transparency. This means the overlay windows with "floating text" are not
supported in the typical X server operation on the HCRX-8[Z], HP [Dual] VISUALIZE-EG or HP
VISUALIZE-8.
For applications that require transparent overlay windows on the HCRX-8[Z], HP VISUALIZE-EG(D)
or HP VISUALIZE-8, an optional X server mode is available to allow for overlay transparency, but it is
restrictive. In this optional mode, overlay colormaps provide a single entry that can be used to render
transparency. Only one hardware colormap is available in the overlays (instead of two) and only one
hardware colormap is available in the image planes (instead of two).
To activate this optional X server mode to enable transparency, set the EnableOverlayTransparency
screen option. You will need to restart the X server for the option to take effect.
With this mode enabled, colormaps created in the default visual have 255 entries; entry 256 is reserved
for transparency. As on the CRX-24[Z] and CRX-48Z, the screen option
CountTransparentInOverlayVisual can be used to include the transparent index in the colormap size
(256 entries instead of 255).
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Programmers' Note
If transparency is not enabled, there are only 252 colors available. Entries 252-255 are not writable, and
should not be used; there are only 252 colormap entries available, even though the server states that
there are 256.
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Graphics Administration Guide for HP-UX 10.20
Page 61