diff --git a/src/dc_screen.c b/src/dc_screen.c
index 31b3197..37d173e 100755
--- a/src/dc_screen.c
+++ b/src/dc_screen.c
@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include "log.h"
 #include "fbinit.h"
 #include "devctxt.h"
 #include "dc_screen.h"
@@ -78,6 +79,15 @@ static BOOL screen_line(PVOID privdata, INT32 x1, INT32 y1, INT32 x2, INT32 y2,
   INT32 tmp;
   PUINT16 loc;
   
+  ASSERT(x1 >= 0);
+  ASSERT(x1 < Fb_Info->width);
+  ASSERT(y1 >= 0);
+  ASSERT(y1 < Fb_Info->height);
+  ASSERT(x2 >= 0);
+  ASSERT(x2 < Fb_Info->width);
+  ASSERT(y2 >= 0);
+  ASSERT(y2 < Fb_Info->height);
+  
   if (ABS(dx) < ABS(dy))
   {
     if (y1 > y2)
diff --git a/src/devctxt.c b/src/devctxt.c
index 83fc8ab..c501005 100755
--- a/src/devctxt.c
+++ b/src/devctxt.c
@@ -1,5 +1,6 @@
 #include <string.h>
 #include <stdlib.h>
+#include "log.h"
 #include "gfxtype.h"
 #include "gfxobj.h"
 #include "devctxt.h"
@@ -23,17 +24,27 @@ static BOOL line_clip(PINT32 output, INT32 x1, INT32 y1, INT32 x2, INT32 y2, INT
   BYTE outcode1, outcode2, tmpb;
   INT32 tmp;
   
+  Log(LDEBUG, "clipping line from (%d, %d) to (%d, %d) against bounding box (%d, %d, %d, %d)", x1 >> 16, y1 >> 16, x2 >> 16, y2 >> 16,
+      xmin >> 16, ymin >> 16, xmax >> 16, ymax >> 16);
+  
   /* Cohen-Sutherland line-clipping algorithm (see Foley & Van Dam, pp. 145-149) */
   for (;;)
   {
     outcode1 = line_clip_outcode(x1, y1, xmin, ymin, xmax, ymax);
 	outcode2 = line_clip_outcode(x2, y2, xmin, ymin, xmax, ymax);
 	if ((outcode1 & outcode2) != 0)
+	{
+	  Log.debug("*REJECT*");
 	  return FALSE; /* trivial rejection */
+	}
 	else if ((outcode1 == 0) && (outcode2 == 0))
+	{
+	  Log.debug("*ACCEPT*");
 	  break; /* trivial acceptance */
+	}
 	if (outcode1 == 0)
 	{
+	  Log(LDEBUG, "exchange points")
 	  tmp = x1;
 	  x1 = x2;
 	  x2 = tmp;
@@ -48,23 +59,28 @@ static BOOL line_clip(PINT32 output, INT32 x1, INT32 y1, INT32 x2, INT32 y2, INT
 	{
 	  x1 += (x2 - x1) * (ymin - y1) / (y2 - y1);
 	  y1 = ymin;
+	  Log.debug("clipped against top to point (%d, %d)", x1 >> 16, y1 >> 16);
 	}
 	else if (outcode1 & 0x4)
 	{
 	  x1 += (x2 - x1) * (ymax - y1) / (y2 - y1);
 	  y1 = ymax;
+	  Log.debug("clipped against bottom to point (%d, %d)", x1 >> 16, y1 >> 16);
 	}
 	else if (outcode1 & 0x2)
 	{
 	  y1 += (y2 - y1) * (xmax - x1) / (x2 - x1);
 	  x1 = xmax;
+	  Log.debug("clipped against right to point (%d, %d)", x1 >> 16, y1 >> 16);
 	}
 	else if (outcode1 & 0x1)
 	{
 	  y1 += (y2 - y1) * (xmin - x1) / (x2 - x1);
 	  x1 = xmin;
+	  Log.debug("clipped against left to point (%d, %d)", x1 >> 16, y1 >> 16);
 	}
   }
+  Log(LDEBUG, "final line is from (%d, %d) to (%d, %d)", x1 >> 16, y1 >> 16, x2 >> 16, y2 >> 16);
   output[0] = x1;
   output[1] = y1;
   output[2] = x2;