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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<gio.h>
+
+# GTEXT -- Draw text.  All textual output via GIO is via this primitive.  Unlike
+# polyline, polymarker, fill area, and cell array output, textual output is not
+# subjected to clipping by GIO.  Clipping may be performed at the kernel level
+# if a workstation viewport is defined.  Our task here is principally to parse
+# the format string and set up the text attributes, then insert the text drawing
+# instruction into the GKI instruction stream.  The real work of text generation
+# is very device dependent and is therefore left to the kernel.
+
+procedure gtext (gp, x, y, text, format)
+
+pointer	gp			# graphics descriptor
+real	x, y			# position at which text is to be drawn
+char	text[ARB]		# text to be drawn
+char	format[ARB]		# text drawing parameters
+
+int	ip, i
+real	mx, my
+pointer	sp, ap, tx
+bool	text_attributes_modified
+
+begin
+	call smark (sp)
+	call salloc (ap, LEN_TX, TY_STRUCT)
+
+	# Set up pointers to text attribute packets and initialize the
+	# new packet to the default values.  Two text attribute packets
+	# are maintained in GP: TXAP, the default packet, and TXAPCUR,
+	# the packet last sent to the device.  In what follows, AP is
+	# the new packet and TX is the packet last sent to the device.
+	# We start by initializing the new packet at AP to the default
+	# text drawing parameters.
+
+	call amovi (Memi[GP_TXAP(gp)], Memi[ap], LEN_TX)
+	tx = GP_TXAPCUR(gp)
+
+	# Parse the format string and set the text attributes.  The code is
+	# more general than need be, i.e., the entire attribute name string
+	# is extracted but only the first character is used.  Whitespace is
+	# permitted and ignored.
+
+	ip = 1
+	call gtxset (ap, format, ip)
+
+	# If the old text attribute packet was never fixed always fix the
+	# new packet, otherwise determine whether or not any text attributes
+	# were actually modified and only fix the new packet if it is
+	# different.
+
+	text_attributes_modified = false
+	for (i=2;  i <= LEN_TX;  i=i+1)
+	    if (Memi[ap+i-1] != Memi[tx+i-1]) {
+		text_attributes_modified = true
+		break
+	    }
+
+	# Flush any buffered polyline output, and transform the text coordinates
+	# to GKI device coordinates.
+
+	call gpl_flush()
+	call gpl_wcstogki (gp, x, y, mx, my)
+
+	# Update text attributes if necessary.
+	if (text_attributes_modified || TX_STATE(tx) != FIXED) {
+	    call amovi (Memi[ap], Memi[tx], LEN_TX)
+	    call gki_txset (GP_FD(gp), tx)
+	    TX_STATE(tx) = FIXED
+	}
+
+	# Output text drawing instruction.
+	call gki_text (GP_FD(gp), nint(mx), nint(my), text)
+
+	call sfree (sp)
+end