Default Visual Assumptions

A common mistake in programming an X11 client is to assume that the default visual has an indexed class (for example, PseudoColor or StaticColor). It is possible for the default visual to be 24-bit TrueColor on some devices. Clients expecting to run on these devices must be prepared to handle this type of default visual.

Other common programming mistakes with visuals are:

• Assuming the default depth is 8

• Assuming the colormap is writable

• Using a default visual that is not appropriate rather than searching for an appropriate visual using XGetVisualInfo

If the device does not support a visual requested by a client, the following error message is returned. In this error message, # represents the depth number requested, and n represents the requested display device. If this message is returned for a supported visual/device combination (as indicated inTable A-1 ), then an installation problem exists.

Error:

cannot provide a default depth #for device

/dev/fbs/n

In general, client applications may need to be modified to make them more portable in the presence of different default visual types.