Use vertex pulling for ceiling stencil

shader/ceiling/stencil.vert

@@ -1,6 +1,18 @@
 #version 450 core
-layout (location = 0) in vec4 poss;
+//layout (location = 0) in vec4 poss;
+//void main()
+//{
+//  gl_Position = poss;
+//}
+struct PosTex { vec4 pospos; vec4 texang; };
+layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
+layout (std430, binding = 2) readonly buffer Pos { PosTex data[]; };
+int indices[6] = {0,1,3,0,3,2};
 void main()
 {
-  gl_Position = poss;
+    vec4 pp = data[gl_VertexID / 6].pospos;
+    int j = indices[gl_VertexID % 6];
+    float z = (j > 1.5 ? 5000 : 100);
+    vec2 xy = (j % 2 > 0 ? pp.xy : pp.zw);
+    gl_Position = theMat * vec4(xy,z,1);
 }