Implement correctly shadows on geometry, with arbitrary near plane cap

shader/lighting/cap.geom

@@ -8,9 +8,9 @@ vec4 projNear (vec4 pos)
     // note we project to a specific height
     // this is quite brittle, not ideal
     vec3 dir = pos.xyz - lightPos ;
-    float a = (150 - pos.z) / dir.z ;
+    float a = (140 - pos.z) / dir.z ;
     vec2 xy = (pos.xyz + a * dir).xy ;
-    return vec4 ( xy, 150 , 1) ;
+    return vec4 ( xy, 140 , 1) ;
 }
 void main()
 {