1 files changed, 68 insertions, 0 deletions
diff --git a/sys/gio/cursor/gtrwritep.x b/sys/gio/cursor/gtrwritep.x
new file mode 100644
index 00000000..d1a3fd4a
--- /dev/null
+++ b/sys/gio/cursor/gtrwritep.x
@@ -0,0 +1,68 @@
+# 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