1 files changed, 36 insertions, 0 deletions
diff --git a/sys/gio/glabax/glbverify.x b/sys/gio/glabax/glbverify.x
new file mode 100644
index 00000000..6666b06a
--- /dev/null
+++ b/sys/gio/glabax/glbverify.x
@@ -0,0 +1,36 @@
+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<mach.h>
+include	<gset.h>
+include	<gio.h>
+include	"glabax.h"
+
+# GLB_VERIFY_LOG_SCALING -- Verify that log scaling makes sense, i.e., that
+# the range covered by an axis compared to its distance from the origin is
+# large enough to permit log scaling.  If log scaling is reasonable check if
+# the window goes negative, and switch to ELOG scaling if such is the case.
+
+procedure glb_verify_log_scaling (gp)
+
+pointer	gp			# graphics descriptor
+pointer	w
+
+begin
+	w  = GP_WCSPTR (gp, GP_WCS(gp))
+
+	# Force ELOG scaling if any data <= 0.
+
+	if (WCS_XTRAN(w) != LINEAR)
+	    if (WCS_WX1(w) <= 0 || WCS_WX2(w) <= 0)
+		WCS_XTRAN(w) = ELOG
+
+	if (WCS_YTRAN(w) != LINEAR)
+	    if (WCS_WY1(w) <= 0 || WCS_WY2(w) <= 0)
+		WCS_YTRAN(w) = ELOG
+
+	# Set the WCS state to modified even if it wasn't.  This is safe
+	# and in any case the WCS is changed in the main glabax routine
+	# shortly after we are called.
+
+	GP_WCSSTATE(gp) = MODIFIED
+end