Correct display of zero values with -logscale 1

In order to do that, improve the clipping functionality in tkbltGrMisc.C
to support infinite coordinates.  It also now provides more information
with regards to its processing, letting tkbltGrElemLine.C use that same
routine instead of duplicade the clipping code.

1 files changed, 75 insertions, 5 deletions

diff --git a/generic/tkbltGrMisc.C b/generic/tkbltGrMisc.C
index d951494..aaafcfd 100644
--- a/generic/tkbltGrMisc.C
+++ b/generic/tkbltGrMisc.C
@@ -39,6 +39,7 @@
 
 #include "tkbltGraph.h"
 #include "tkbltGrMisc.h"
+#include "tkbltInt.h"
 
 using namespace Blt;
 
@@ -70,6 +71,63 @@ int Blt::pointInPolygon(Point2d *s, Point2d *points, int nPoints)
   return (count & 0x01);
 }
 
+/*
+ *---------------------------------------------------------------------------
+ *      Clips a rectangle in one direction where some of the coordinates are
+ *      infinite.
+ *---------------------------------------------------------------------------
+ */
+static LineRectClipResult ClipInfinity (double *pa, double *pb, double *qa, double *qb, double region_min, double region_max)
+{
+  int finitepa = isfinite(*pa);
+  int finiteqa = isfinite(*qa);
+
+  if (!finitepa) {
+    if (finiteqa) {
+      if (*pa > 0) {		// +Inf
+	*pa = region_max;
+      } else if (*pa < 0) {	// -Inf
+	*pa = region_min;
+      } else {			// NaN
+	return CLIP_OUTSIDE;
+      }
+      // *qa is finite, simplify to zero slope at *pb.
+      *pb = *qb;
+      return CLIP_P;
+    } else {			// Both infinite.
+      int positivepa = *pa > 0;
+      int positiveqa = *qa > 0;
+
+      if (positivepa < positiveqa) { // (p,q) ~ (-Inf,Inf)
+	*pa = region_min;
+	*qa = region_max;
+      } else if (positivepa > positiveqa) { // (p,q) ~ (Inf,-Inf)
+	*pa = region_max;
+	*qa = region_min;
+      } else {			// (Inf,Inf), (-Inf,-Inf) or NaN.
+	return CLIP_OUTSIDE;
+      }
+      // At opposite infinities; simplify to zero slope in the middle.
+      *pb = *qb = (*pb + *qb) / 2.0;
+      return CLIP_P | CLIP_Q;
+    }
+  } else if (!finiteqa) {
+    // *pa is finite.
+    if (*qa > 0) {		// +Inf
+      *qa = region_max;
+    } else if (*qa < 0) {	// -Inf
+      *qa = region_min;
+    } else {			// NaN
+      return CLIP_OUTSIDE;
+    }
+    // *pa is finite, simplify to zero slope at *qb.
+    *qb = *pb;
+    return CLIP_Q;
+  }
+  return CLIP_OUTSIDE;
+}
+
+
 static int ClipTest (double ds, double dr, double *t1, double *t2)
 {
   double t;
@@ -77,7 +135,7 @@ static int ClipTest (double ds, double dr, double *t1, double *t2)
   if (ds < 0.0) {
     t = dr / ds;
     if (t > *t2) {
-      return 0;
+      return 0;			/* Line is outside clipping edge */
     } 
     if (t > *t1) {
       *t1 = t;
@@ -85,7 +143,7 @@ static int ClipTest (double ds, double dr, double *t1, double *t2)
   } else if (ds > 0.0) {
     t = dr / ds;
     if (t < *t1) {
-      return 0;
+      return 0;			/* Line is outside clipping edge */
     } 
     if (t < *t2) {
       *t2 = t;
@@ -105,35 +163,47 @@ static int ClipTest (double ds, double dr, double *t1, double *t2)
  *	of the clipped line segment are returned.  The original coordinates
  *	are overwritten.
  *
+ *      The return value indicates whether the line was completely outside of
+ *      the region, returning CLIP_OUTSIDE; or at least partly inside, returning
+ *      CLIP_INSIDE.  In the latter case, the result might be or'ed with CLIP_P
+ *      if p coordinates were clipped, or CLIP_Q if q coordinates were.
+ *
  *	Reference: 
  *	  Liang, Y-D., and B. Barsky, A new concept and method for
  *	  Line Clipping, ACM, TOG,3(1), 1984, pp.1-22.
  *---------------------------------------------------------------------------
  */
-int Blt::lineRectClip(Region2d* regionPtr, Point2d *p, Point2d *q)
+LineRectClipResult Blt::lineRectClip(Region2d* regionPtr, Point2d *p, Point2d *q)
 {
   double t1, t2;
   double dx, dy;
+  LineRectClipResult res = CLIP_OUTSIDE;
+
+  res |= ClipInfinity(&p->x, &p->y, &q->x, &q->y, regionPtr->bottom, regionPtr->top);
 
   t1 = 0.0, t2 = 1.0;
   dx = q->x - p->x;
   if ((ClipTest (-dx, p->x - regionPtr->left, &t1, &t2)) &&
       (ClipTest (dx, regionPtr->right - p->x, &t1, &t2))) {
+    res |= ClipInfinity(&p->y, &p->x, &q->y, &q->x, regionPtr->top, regionPtr->bottom);
+
     dy = q->y - p->y;
     if ((ClipTest (-dy, p->y - regionPtr->top, &t1, &t2)) && 
 	(ClipTest (dy, regionPtr->bottom - p->y, &t1, &t2))) {
       if (t2 < 1.0) {
 	q->x = p->x + t2 * dx;
 	q->y = p->y + t2 * dy;
+	res |= CLIP_Q;
       }
       if (t1 > 0.0) {
 	p->x += t1 * dx;
 	p->y += t1 * dy;
+	res |= CLIP_P;
       }
-      return 1;
+      return res | CLIP_INSIDE;
     }
   }
-  return 0;
+  return CLIP_OUTSIDE;
 }
 
 /*