Initial pass at shadows from level geometry

shader/lighting/lineShadow.geom

@@ -1,5 +1,5 @@
 #version 430 core
-layout (lines) in;
+layout (lines_adjacency) in;
 layout (triangle_strip, max_vertices = 4) out;
 layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
 uniform vec3 lightPos;
@@ -8,12 +8,25 @@ vec4 f (vec4 p) {return (theMat * p);}
 void main()
 {
     vec4 p0 = gl_in[0].gl_Position;
-    gl_Position = f(p0); EmitVertex();
-    vec4 p1 = gl_in[1].gl_Position;
-    gl_Position = f(p1); EmitVertex();
-    vec4 p2 = shift(p0);
-    gl_Position = f(p2); EmitVertex();
-    vec4 p3 = shift(p1);
-    gl_Position = f(p3); EmitVertex();
-    EndPrimitive();
+    vec3 n0 = gl_in[2].gl_Position.xyz;
+    vec3 n1 = gl_in[3].gl_Position.xyz;
+    vec3 lightDir = p0.xyz - lightPos.xyz;
+    if ( dot(n0 , lightDir) * dot(n1 , lightDir) < 0 );
+    {
+        gl_Position = f(p0); EmitVertex();
+        vec4 p1 = gl_in[1].gl_Position;
+        gl_Position = f(p1); EmitVertex();
+        vec4 p2 = shift(p0);
+        gl_Position = f(p2); EmitVertex();
+        vec4 p3 = shift(p1);
+        gl_Position = f(p3); EmitVertex();
+        EndPrimitive();
+    }
+    {
+    }
+    //gl_Position = vec4 (0,0,-0.5,1); EmitVertex();
+    //gl_Position = vec4 (1,0,-0.5,1); EmitVertex();
+    //gl_Position = vec4 (1,1,1,1); EmitVertex();
+    //gl_Position = vec4 (0,1,1,1); EmitVertex();
+    //EndPrimitive();
 }