Improve window drawing

shader/pull/window.frag

@@ -10,5 +10,4 @@ void main()
   float cloudz = texture(cloudpos, vScreenPos).z;
   fColOverCloud = ( cloudz > vPos.z ? vec4(0) : vCol);
   fColUnderCloud = ( cloudz > vPos.z ? vCol : vec4(0));
-  fColUnderCloud = vec4(0);
 }

shader/pull/window.vert

@@ -5,18 +5,22 @@ layout (std430, binding = 1) readonly buffer Pos { PosCol data[]; };
 out vec4 vCol;
 out vec4 vPos;
 out vec2 vScreenPos;
-//int indices[6] = {0,1,3,0,3,2};
 int indices[6] = 
     {0,3,1
     ,0,2,3};
 // note reversed compared to walls
 void main()
 {
-    vCol = data[gl_VertexID / 6].col;
-    vec4 pp = data[gl_VertexID / 6].pospos;
+    vCol = data[gl_VertexID / 12].col;
+    vec4 pp = data[gl_VertexID / 12].pospos;
     int j = indices[gl_VertexID % 6];
-    //float z = (j > 1.5 ? 5000 : 0);
-    float z = (j > 1.5 ? 200 : 0);
+    bool t = gl_VertexID % 12 > 5.5;
+    float z = (j > 1.5 
+            ? (t ? 100 : 5000)
+            : (t ?   0 :  100)
+            );
+    // we draw two quads: one which can be below clouds,
+    // and one which is always above
     vec2 xy = (j % 2 > 0 ? pp.xy : pp.zw);
     vPos = vec4( xy, z, 1);
     gl_Position = theMat * vPos;