Mostly details completing the previous two commits.

Eliminating SMALL_TOLERANCE in addition to MIN_ISECT_DIST. This partly
follows up on a question Jerome asked either in POV-Ray#358 or some related issue.
Namely, why not zero or near it for the Intersect_BBox_Dir calls in
object.cpp. Larger values do indeed cause artifacts with secondary rays as
especially noticeable in scenes with media. It's one of many causes for
media speckles. Pull POV-Ray#358 as originally submitted moved from a
MIN_ISECT_DIST value of 1e-4 to SMALL_TOLERANCE of 1e-3 making the inherent
problem worse. SMALL_TOLERANCE had also been adopted a few other places in
the code. In those cases moved to gkDBL_epsilon or gkMinIsectDepthReturned
as appropriate.

Author: wfpokorny

source/core/configcore.h

@@ -179,11 +179,6 @@
     #define BOUND_HUGE 2.0e+10
 #endif
 
-/// @def SMALL_TOLERANCE
-/// Minimum distance that qualifies as ray-object intersection.
-///
-#define SMALL_TOLERANCE 0.001
-
 /// @def MAX_DISTANCE
 /// Maximum distance that qualifies as ray-object intersection.
 ///

source/core/material/media.cpp

@@ -8,7 +8,7 @@
 /// @parblock
 ///
 /// Persistence of Vision Ray Tracer ('POV-Ray') version 3.8.
-/// Copyright 1991-2018 Persistence of Vision Raytracer Pty. Ltd.
+/// Copyright 1991-2019 Persistence of Vision Raytracer Pty. Ltd.
 ///
 /// POV-Ray is free software: you can redistribute it and/or modify
 /// it under the terms of the GNU Affero General Public License as
@@ -714,7 +714,7 @@ void MediaFunction::ComputeOneMediaLightInterval(LightSource *light, LightSource
     {
         case CYLINDER_SOURCE:
             if(ComputeCylinderLightInterval(ray, light, &t1, &t2))
-                insert = ((t1 < isect.Depth) && (t2 > SMALL_TOLERANCE));
+                insert = ((t1 < isect.Depth) && (t2 > gkMinIsectDepthReturned));
             break;
         case POINT_SOURCE:
             t1 = 0.0;
@@ -723,7 +723,7 @@ void MediaFunction::ComputeOneMediaLightInterval(LightSource *light, LightSource
             break;
         case SPOT_SOURCE:
             if(ComputeSpotLightInterval(ray, light, &t1, &t2))
-                insert = ((t1 < isect.Depth) && (t2 > SMALL_TOLERANCE));
+                insert = ((t1 < isect.Depth) && (t2 > gkMinIsectDepthReturned));
             break;
     }
 

source/core/scene/object.cpp

@@ -903,25 +903,25 @@ ObjectPtr CompoundObject::Invert()
 
 bool ObjectBase::Intersect_BBox(BBoxDirection variant, const BBoxVector3d& origin, const BBoxVector3d& invdir, BBoxScalar maxd) const
 {
-    // reverted to SMALL_TOLERANCE over v3.7 MIN_ISECT_DEPTH, for FS324 [jg] old code [trf]
+    // gkDBL_epsilon(4.4e-16) now used over SMALL_TOLERANCE(1e-3) or v3.7 MIN_ISECT_DEPTH(1e-4).
     switch(variant)
     {
         case BBOX_DIR_X0Y0Z0: // 000
-            return Intersect_BBox_Dir<0, 0, 0>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<0, 0, 0>(BBox, origin, invdir, gkDBL_epsilon, maxd);
         case BBOX_DIR_X0Y0Z1: // 001
-            return Intersect_BBox_Dir<0, 0, 1>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<0, 0, 1>(BBox, origin, invdir, gkDBL_epsilon, maxd);
         case BBOX_DIR_X0Y1Z0: // 010
-            return Intersect_BBox_Dir<0, 1, 0>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<0, 1, 0>(BBox, origin, invdir, gkDBL_epsilon, maxd);
         case BBOX_DIR_X0Y1Z1: // 011
-            return Intersect_BBox_Dir<0, 1, 1>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<0, 1, 1>(BBox, origin, invdir, gkDBL_epsilon, maxd);
         case BBOX_DIR_X1Y0Z0: // 100
-            return Intersect_BBox_Dir<1, 0, 0>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<1, 0, 0>(BBox, origin, invdir, gkDBL_epsilon, maxd);
         case BBOX_DIR_X1Y0Z1: // 101
-            return Intersect_BBox_Dir<1, 0, 1>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<1, 0, 1>(BBox, origin, invdir, gkDBL_epsilon, maxd);
         case BBOX_DIR_X1Y1Z0: // 110
-            return Intersect_BBox_Dir<1, 1, 0>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<1, 1, 0>(BBox, origin, invdir, gkDBL_epsilon, maxd);
         case BBOX_DIR_X1Y1Z1: // 111
-            return Intersect_BBox_Dir<1, 1, 1>(BBox, origin, invdir, SMALL_TOLERANCE, maxd);
+            return Intersect_BBox_Dir<1, 1, 1>(BBox, origin, invdir, gkDBL_epsilon, maxd);
     }
 
     return false; // unreachable

source/core/shape/blob.cpp

@@ -294,7 +294,7 @@ bool Blob::All_Intersections(const Ray& ray, IStack& Depth_Stack, TraceThreadDat
 
     /* To avoid numerical problems we start at the first interval. */
 
-    if ((start_dist = intervals[0].bound) < SMALL_TOLERANCE)
+    if ((start_dist = intervals[0].bound) < gkMinIsectDepthReturned)
     {
         start_dist = 0.0;
     }

source/core/shape/disc.cpp

@@ -10,7 +10,7 @@
 /// @parblock
 ///
 /// Persistence of Vision Ray Tracer ('POV-Ray') version 3.8.
-/// Copyright 1991-2017 Persistence of Vision Raytracer Pty. Ltd.
+/// Copyright 1991-2019 Persistence of Vision Raytracer Pty. Ltd.
 ///
 /// POV-Ray is free software: you can redistribute it and/or modify
 /// it under the terms of the GNU Affero General Public License as
@@ -431,7 +431,7 @@ Disc::Disc() : ObjectBase(DISC_OBJECT)
 
     /* Default bounds */
 
-    Make_BBox(BBox, -1.0, -1.0, -SMALL_TOLERANCE, 2.0,  2.0, 2.0 * SMALL_TOLERANCE);
+    Make_BBox(BBox, -1.0, -1.0, -gkMinIsectDepthReturned, 2.0,  2.0, 2.0 * gkMinIsectDepthReturned);
 }
 
 
@@ -581,7 +581,8 @@ void Disc::Compute_BBox()
 
     rad = sqrt(oradius2);
 
-    Make_BBox(BBox, -rad, -rad, -SMALL_TOLERANCE, 2.0*rad, 2.0*rad, 2.0*SMALL_TOLERANCE);
+    Make_BBox(BBox, -rad, -rad, -gkMinIsectDepthReturned,
+              2.0*rad, 2.0*rad, 2.0*gkMinIsectDepthReturned);
 
     Recompute_BBox(&BBox, Trans);
 }

source/core/shape/polygon.cpp

@@ -10,7 +10,7 @@
 /// @parblock
 ///
 /// Persistence of Vision Ray Tracer ('POV-Ray') version 3.8.
-/// Copyright 1991-2018 Persistence of Vision Raytracer Pty. Ltd.
+/// Copyright 1991-2019 Persistence of Vision Raytracer Pty. Ltd.
 ///
 /// POV-Ray is free software: you can redistribute it and/or modify
 /// it under the terms of the GNU Affero General Public License as
@@ -817,22 +817,22 @@ void Polygon::Compute_BBox()
 
     Make_BBox_from_min_max(BBox, Min, Max);
 
-    if (fabs(BBox.size[X]) < SMALL_TOLERANCE)
+    if (fabs(BBox.size[X]) < gkMinIsectDepthReturned)
     {
-        BBox.lowerLeft[X] -= SMALL_TOLERANCE;
-        BBox.size[X]    += 2.0 * SMALL_TOLERANCE;
+        BBox.lowerLeft[X] -= gkMinIsectDepthReturned;
+        BBox.size[X]    += 2.0 * gkMinIsectDepthReturned;
     }
 
-    if (fabs(BBox.size[Y]) < SMALL_TOLERANCE)
+    if (fabs(BBox.size[Y]) < gkMinIsectDepthReturned)
     {
-        BBox.lowerLeft[Y] -= SMALL_TOLERANCE;
-        BBox.size[Y]    += 2.0 * SMALL_TOLERANCE;
+        BBox.lowerLeft[Y] -= gkMinIsectDepthReturned;
+        BBox.size[Y]    += 2.0 * gkMinIsectDepthReturned;
     }
 
-    if (fabs(BBox.size[Z]) < SMALL_TOLERANCE)
+    if (fabs(BBox.size[Z]) < gkMinIsectDepthReturned)
     {
-        BBox.lowerLeft[Z] -= SMALL_TOLERANCE;
-        BBox.size[Z]    += 2.0 * SMALL_TOLERANCE;
+        BBox.lowerLeft[Z] -= gkMinIsectDepthReturned;
+        BBox.size[Z]    += 2.0 * gkMinIsectDepthReturned;
     }
 }