This predicate returns
#t if the graphics system named by the
symbol graphics-device-type is implemented by the Scheme system.
Otherwise it returns
#f, in which case it is an error to attempt
to make a graphics device using graphics-device-type.
This procedure returns a list of symbols which are the names of all the
graphics device types that are supported by the Scheme system. The
result is useful in deciding what additional arguments to supply to
make-graphics-device, as each device type typically has a unique
way of specifying the initial size, shape and other attributes.
This operation creates and returns a graphics device object.
Graphics-device-type is a symbol naming a graphics device type,
and both the number and the meaning of the remaining arguments is
determined by that type (see the description of each device type for
details); graphics-device-type must satisfy
graphics-type-available?. Graphics-device-type may also be
#f, in which case the graphics device type is chosen by the
system from what is available. This allows completely portable graphics
programs to be written provided no custom graphics operations are used.
When graphics-device-type is
#f no further arguments may be
given; each graphics device type will use some “sensible” defaults.
If more control is required then the program should use one of the two
procedures above to dispatch on the available types.
This procedure opens and initializes the device, which remains valid
until explicitly closed by the procedure
Depending on the implementation of the graphics device, if this object
is reclaimed by the garbage collector, the graphics device may remain
open or it may be automatically closed. While a graphics device remains
open the resources associated with it are not released.
Closes graphics-device, releasing its resources. Subsequently it is an error to use graphics-device.