Add wall drawing capability (for shadows)

shader/wallShadow.frag

@@ -3,5 +3,5 @@ out vec4 fColor;
 
 void main()
 {
-  fColor = vec4 (0.9,0.9,0,1);
+  fColor = vec4 (0.9,0.5,0,1);
 }

shader/wallShadow.geom

@@ -9,17 +9,16 @@ void main()
 {
   vec2 posa = gl_in[0].gl_Position.xy;
   vec2 posb = gl_in[0].gl_Position.zw;
-  vec2 v = normalize( posb - posa);
-  vec2 off = vec2( -(v.y *0.2) 
-                 , v.x *0.2 );
+  vec2 posc = vBackPoss[0].xy;
+  vec2 posd = vBackPoss[0].zw;
 
-  gl_Position = vec4 (posa, 0 , 1);
+  gl_Position = vec4 (posa, -1 , 1);
   EmitVertex();
-  gl_Position = vec4 (posb, 0 , 1);
+  gl_Position = vec4 (posb, -1 , 1);
   EmitVertex();
-  gl_Position = vec4 (posa + off, 0 , 1);
+  gl_Position = vec4 (posc, -1 , 1);
   EmitVertex();
-  gl_Position = vec4 (posb + off, 0 , 1);
+  gl_Position = vec4 (posd, -1 , 1);
   EmitVertex();
 
   EndPrimitive();