Silicon Graphics IRIS Workstation, Руководство пользователя

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156 IRIS WORKSTATION GUIDE
Version 1.0
Appendix L:
compacted, depending on how much space can be recovered. The new routine
compactify(object)
gives users explicit control of the compactification.
With the ability to program the terminal, display list editing becomes much less
important. With the GL 2 hardware, it will become even less so. In principle,
terminal programmers can develop their own display list structure and
interpreters.
Tag handling
GL 2 will make the following changes to object editing:
1. Every object automatically has two tags marking the beginning and
end of the object STARTTAG and ENDTAG . These tags cannot be
deleted, and no items can be added before the first nor after the last
tag. One can begin an insertion following ENDTAG , but as each
item is added, ENDTAG moves to the end of the object.
2. There are no offsets in object editing commands. All deletions are
tag-to-tag. All insertions and replacements begin immediately
following a tag. The delete command is now:
delete(tag1, tag2)
;
the replace and insert commands become:
replace(tag)
and
insert(tag)
.
3. To edit between two tags, we provide the command
newtag(newtag,
oldtag, offset)
that makes a new tag offset commands ahead of
oldtag .
4. Tags retain their ordering. In GL 1, if tag1 and tag2 point to the
same place within a display list, it is impossible to insert items after
tag1 but before tag2 . In GL 2, even if there are no items between
tag1 and tag2 , but tag1 is before tag2 ,
insert (tag1)
will add items
between the two tags. In GL 2, tags can be thought of as being
physically in the display list.
5. There is a
deletetag(tag)
routine.
L.3 Picking
Picking has changed considerably. You now have explicit control of a name
stack with
pushname(name)
,
loadname(name)
, and
popname()
. Names are 16 bits
long; if you need more than 16 bits, call
pushname()
more than once. A hit in
pick/select mode returns the entire name stack.
The buffers for
endpick(buffer)
and
endselect(buffer)
consist of name-lists of
16-bit names each corresponding to a single hit. The first number in each
name-list is the length of the name-list. The
endpick()
and
endselect()
routines return the number of name-lists. If it returns a positive number, then
all the hit data is in the buffer; if it is negative, its magnitude is the number of
valid name-lists in the buffer—there was not enough room in the buffer to