This application selects the first, i.e.
oldest, unobstructed FRAME
picture in the graphics database
for a graphics device. Unobstructed means that there
is no younger picture overlying it either wholly or in part.
DEVICE = DEVICE (Read)
The graphics workstation.
picvis This selects the first unobscured FRAME
picture for the current graphics device.
picvis xwindows This selects the
first unobscured FRAME picture for the xwindows graphics device.
An error is returned if there is no unobscured FRAME picture, and the current picture
This routine cannot know whether or a picture has been cleared, and hence is safe
to reuse, as such information is not stored in the graphics database.
The execution time is approximately proportional to a linear
combination of the number of pictures in the database before the unobstructed FRAME
picture is found, and the square of the number of pictures in the database.