This application selects the first, i.e.
picture in the graphics database
for a graphics device, subject to the following
criterion. The picture must not obstruct any other picture except the BASE, and must
itself not be obstructed. Unobstructed means that there is no younger picture
overlying it either wholly or in part. This means that plotting can occur within
the selected FRAME picture without overwriting or obscuring earlier plots.
DEVICE = DEVICE (Read)
[The current graphics device
selects the first unobscured and unobscuring FRAME picture for the current
picentire xwindows This selects the first unobscured
and unobscuring FRAME picture for the xwindows graphics device.
An error is returned if there is no suitable 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.