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File indexing completed on 2026-04-09 07:48:54
0001 #pragma once 0002 0003 /** 0004 intersect_leaf_halfspace 0005 -------------------------- 0006 0007 Define CSG_HALFSPACE with a unit normal *n* and a distance *w* from the origin 0008 in the normal direction. Hence points *p* that are within the plane fulfil:: 0009 0010 p.n = w 0011 0012 \ * 0013 +\ * 0014 ++\ * 0015 +++\ * 0016 ++++\ * 0017 +++++\ * 0018 ++++++\ * n outwards pointing normal, away from halfspace 0019 +++++++\ * . 0020 ++++++++\ * . 0021 +++++++++\ * . 0022 ++++++++++\ . 0023 +++++++++++O * 0024 ++++++++++++\ * 0025 +++++++++++++\ * 0026 ++ inside ++++\ * outside 0027 +++++++++++++++\ * 0028 ++++++++++++++++\ * +-> 0029 +++++++++++++++++\ * d.n > 0 : direction with normal : heading away from halfspace 0030 ++++++++++++++++++\ * o.n > w : origin outside halfspace 0031 +++++++++++++++++++\ * [no isect, dn*(on-w) > 0] 0032 ++++++++++++++++++++\ * 0033 +++++++++++++++++++++\ * <-+ 0034 ++++++++++++++++++++++\ * d.n < 0 : direction against normal : heading towards halfspace 0035 +++++++++++++++++++++++\ * o.n > w : origin outside halfspace 0036 ++++++++++++++++++++++++\ * [poss isect, dn*(on-w) < 0] 0037 \ * 0038 +-> \ * 0039 d.n > 0 \ * 0040 o.n < w \ * 0041 [poss isect, dn*(on-w) < 0] \ * 0042 \ * + 0043 <-+ \ * \ d.n = 0 : direction parallel to plane, perpendicular to normal 0044 d.n < 0 \ * \ o.n - w > 0 : origin outside halfspace 0045 o.n < w \ * [no isect, no exit at infinity as not inside] 0046 [no isect, dn*(on-w) > 0] \ * 0047 [exit at infinity] \ * 0048 \ + 0049 \ \ d.n = 0 : d perp to n 0050 + \ \ o.n - w = 0 : o within plane 0051 \ \ * [infinite isects, exit at infinity] 0052 \ \ * 0053 d.n = 0 : d perp to n 0054 o.n - w < 0 : o inside 0055 [no isect, exit at infinity] 0056 0057 0058 Parametric ray:: 0059 0060 p = o + d t 0061 0062 0063 0064 Intersects of ray with plane:: 0065 0066 p.n = w 0067 0068 (o + d t).n = w 0069 0070 0071 ( w - o.n ) 0072 => t = ------------- 0073 d.n 0074 0075 0076 Rays with origin inside the halfspace that are headed 0077 away from the plane cannot intersect with it. 0078 But the CSG intersection algorithm needs to: 0079 0080 1. classify every ray constituent trial into ENTER/EXIT/MISS 0081 2. every shape needs an "other" side 0082 0083 This these rays can be regarded to EXIT the halfspace at infinity. 0084 This is an UNBOUNDED_EXIT. 0085 0086 o.n < w , (on-w) < 0 origin inside halfspace 0087 d.n < 0 d into halfspace [no isect, exit at infinity] 0088 d.n = 0 d parallel to plane [no isect, exit at infinity] 0089 0090 o.n = w , (on-w) = 0 origin on plane 0091 d.n < 0 d into halfspace [invalid t=0 isect, exit at infinity] 0092 d.n = 0 d within plane, perp to normal [infinite isect, exit at infinity] 0093 0094 Can select both the above situations with "<=":: 0095 0096 ( on-w ) <= 0 && dn <= 0 0097 0098 0099 0100 Consider a test halfspace, defined by n [1/sqrt(2), 1/sqrt(2), 0, 0] 0101 The normal points away from the halfspace, so intersecting a cylinder 0102 with axis in z-direction with this expect to get half a cylinder:: 0103 0104 Y 0105 + . | n 0106 + + . | . 0107 + + + . | . 0108 + + + + 0------X 0109 + + + + +. 0110 + + + + + +. 0111 + + + + + + +. 0112 + + + + + + + +. 0113 0114 Set GEOM to "LocalPolyconeWithPhiCut" and do the conversion:: 0115 0116 ~/o/g4cx/tests/G4CX_U4TreeCreateCSGFoundryTest.sh 0117 0118 Viewing that from different positions:: 0119 0120 NOXGEOM=1 EYE=4,0,10 UP=0,1,0 cxr_min.sh # expected half cylinder, with cut side pointing to +x+ 0121 0122 NOXGEOM=1 EYE=0,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # UNEXPECTED FULL CYLINDER 0123 NOXGEOM=1 EYE=1e-50,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # UNEXPECTED FULL CYLINDER 0124 NOXGEOM=1 EYE=1e-40,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # UNEXPECTED FULL CYLINDER 0125 NOXGEOM=1 EYE=1e-37,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # UNEXPECTED FULL CYLINDER 0126 0127 NOXGEOM=1 EYE=1e-36,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0128 NOXGEOM=1 EYE=1e-35,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0129 NOXGEOM=1 EYE=1e-30,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0130 NOXGEOM=1 EYE=0.001,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0131 NOXGEOM=1 EYE=0.01,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0132 NOXGEOM=1 EYE=0.1,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0133 NOXGEOM=1 EYE=0.2,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0134 NOXGEOM=1 EYE=0.5,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0135 NOXGEOM=1 EYE=1,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0136 NOXGEOM=1 EYE=4,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0137 NOXGEOM=1 EYE=20,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # still expected 0138 0139 0140 After using eps 1e-7 gets worse:: 0141 0142 NOXGEOM=1 EYE=1e-6,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # UNEXPECTED FULL CYLINDER 0143 NOXGEOM=1 EYE=1e-5,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0144 0145 Tweaking, not much diff:: 0146 0147 NOXGEOM=1 EYE=1e-8,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # UNEXPECTED FULL CYLINDER 0148 NOXGEOM=1 EYE=1,0,10 EXTENT_FUDGE=2 CAM=orthographic UP=0,1,0 cxr_min.sh # expected half cylinder 0149 0150 Proceed to CSG/tests/csg_intersect_prim_test.sh which so far has not reproduced the issue. 0151 0152 **/ 0153 0154 0155 LEAF_FUNC 0156 void intersect_leaf_halfspace( bool& valid_isect, float4& isect, const quad& q0, const float t_min, const float3& o, const float3& d ) 0157 { 0158 float3 n = make_float3(q0.f.x, q0.f.y, q0.f.z); 0159 float w = q0.f.w; 0160 0161 float on = dot(o,n); 0162 float dn = dot(d,n); 0163 float on_w = on - w; 0164 float adn = fabsf(dn); 0165 0166 float eps = 1e-9f; 0167 bool inside = on_w < -eps ; 0168 0169 float t = adn > 0.f ? -on_w / dn : t_min ; 0170 valid_isect = t > t_min ; 0171 0172 if (valid_isect) 0173 { 0174 isect.x = n.x ; 0175 isect.y = n.y ; 0176 isect.z = n.z ; 0177 isect.w = t ; 0178 } 0179 else 0180 { 0181 if (inside) 0182 { 0183 isect.y = -0.f; 0184 } 0185 } 0186 0187 #ifdef DEBUG_HALFSPACE 0188 bool yflip = valid_isect == false && isect.y == -0.f ; 0189 printf("//intersect_leaf_halfspace n [%8.3f,%8.3f,%8.3f,%8.3f] o [%8.3f,%8.3f,%8.3f] d[%8.3f,%8.3f,%8.3f] on/dn/on_w/adn [%8.3f,%8.3f,%8.3f,%8.3f] t %8.3f valid_isect %d inside %d yflip %d \n", 0190 n.x, n.y, n.z, w, o.x, o.y, o.z, d.x, d.y, d.z, on,dn,on_w,adn,eps,t, valid_isect, inside, yflip); 0191 #endif 0192 0193 } 0194
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