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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <syserr.h>
include <error.h>
include <gio.h>
include <gki.h>
include "gtr.h"
# GTR_WRITEP -- Virtually write (append) to the graphics frame buffer. Return a
# pointer to the start of the area reserved for the data and advance the
# output pointer beyond the new data area. The use of a buffer pointer here
# yields a very efficient graphics i/o dataflow. For the stdgraph kernel,
# XMIT (pr_psio) places a block of metacode directly in the frame buffer at
# the memory location we point to. GIOTR is then called to process the new
# data block. GIOTR calls GTR_FETCH, which "fetches" the next instruction
# by merely returning a pointer into the frame buffer. The stdgraph kernel
# is then called to execute the instruction. Hence in the simple case, there
# are no memory to memory copies and the contents of an instruction are
# touched only by the kernel.
pointer procedure gtr_writep (fd, nchars)
int fd # graphics stream
int nchars # nchars to reserve at end of buffer
pointer tr, bufp, top, segp
int blen, nwords, ip_offset, op_offset
errchk syserr, realloc
include "gtr.com"
begin
tr = trdes[fd]
if (tr == NULL)
call syserr (SYS_GWRITEP)
nwords = nchars / SZ_SHORT
bufp = TR_FRAMEBUF(tr)
blen = TR_LENFRAMEBUF(tr)
segp = TR_OP(tr) # pointer to next segment
top = bufp + blen
# Make space available in the buffer. We must always allocate the
# requested space, even if the result is a buffer larger than the
# (soft) maximum size permitted. Buffer space will be returned
# after GIOTR processes the new instructions if the buffer grows
# too large.
if (nwords > top - segp) {
# Note that realloc may move the buffer, hence we must adjust any
# pointers into the buffer after the call to realloc.
ip_offset = TR_IP(tr) - bufp
op_offset = segp - bufp
blen = blen + max (INC_LENFRAMEBUF, nwords)
call realloc (bufp, blen, TY_SHORT)
TR_FRAMEBUF(tr) = bufp
TR_LENFRAMEBUF(tr) = blen
TR_IP(tr) = bufp + ip_offset
segp = bufp + op_offset
}
TR_OP(tr) = segp + nwords
TR_LASTOP(tr) = TR_OP(tr)
return (segp)
end
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