Working (but slow) shadow shapes

shader/lighting/cap.geom

@@ -3,6 +3,7 @@ layout (triangles) in;
 layout (triangle_strip, max_vertices = 3) out;
 layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
 uniform vec3 lightPos;
+// this code is duplicated in lineShadow.geom, should not be changed on its own
 vec4 projNear (vec4 pos)
 {
     // note we project to a specific height

shader/lighting/lineShadow.geom

@@ -4,7 +4,7 @@ layout (triangle_strip, max_vertices = 4) out;
 layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
 uniform vec3 lightPos;
 vec4 shift (vec4 p) { return (vec4 (p.xyz + (100000*(p.xyz-lightPos)), 1));}
-// copied from lighting/cap.geom
+// copied from lighting/cap.geom, should not be changed on its own
 vec4 projNear (vec4 pos)
 {
     // note we project to a specific height
@@ -21,13 +21,16 @@ vec4 shiftNear (vec4 pos)
     else
     { return sp ; }
 }
-
 vec4 f (vec4 p) {return (theMat * p);}
 void main()
 {
     vec4 p0 = gl_in[0].gl_Position;
-    vec3 n0 = gl_in[2].gl_Position.xyz;
-    vec3 n1 = gl_in[3].gl_Position.xyz;
+    vec4 p1 = gl_in[1].gl_Position;
+    vec3 n0a = gl_in[2].gl_Position.xyz;
+    vec3 n1a = gl_in[3].gl_Position.xyz;
+    vec3 n0 = cross(p1.xyz - p0.xyz, n0a - p0.xyz) ;
+    vec3 n1 = cross(p0.xyz - p1.xyz, n1a - p1.xyz) ;
+    
     //vec3 n2 = n0 + n1; // assumes the summands are normalized
     vec3 lightDir = p0.xyz - lightPos.xyz;
     // first test if the edge is part of the silhouette
@@ -35,7 +38,6 @@ void main()
     // "different directions" wrt the light direction
     if ( dot(n0 , lightDir) * dot(n1 , lightDir) < 0 )
     {
-        vec4 p1 = gl_in[1].gl_Position;
         vec4 p2 = shiftNear(p0);
         vec4 p3 = shiftNear(p1);
         if ( dot(n0 , lightDir) > 0)