Use vertex pulling for wall shadows

shader/ceiling/stencil.vert

@@ -12,7 +12,7 @@ void main()
 {
     vec4 pp = data[gl_VertexID / 6].pospos;
     int j = indices[gl_VertexID % 6];
-    float z = (j > 1.5 ? 5000 : 100);
+    float z = (j / 2 > 0.5 ? 5000 : 100);
     vec2 xy = (j % 2 > 0 ? pp.xy : pp.zw);
     gl_Position = theMat * vec4(xy,z,1);
 }

shader/lighting/wallShadow.vert

@@ -1,6 +1,39 @@
 #version 450 core
-layout (location = 0) in vec4 poss;
-void main()
-{
-  gl_Position = 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[]; };
+layout(location=0) uniform vec3 lightPos;
+layout(location=1) uniform float rad;
+int indices[18] = 
+    {5,1,7      //    6----7
+    ,7,1,3      //   /|   /|
+    ,7,3,6      //  2-+--3 |
+    ,6,3,2      //  | 4  | 5
+    ,6,2,4      //  0    1  
+    ,4,2,0
+    };
+vec2 shift(vec2 p) {
+  return vec2(lightPos.xy + (rad * normalize(p - lightPos.xy)));
+}
+float detV(vec2 p, vec2 q) {
+    return p.x*q.y - p.y*q.x;
+}
+float isLHS(vec2 p, vec2 q) {
+  return sign(-detV(p,q));
+}
+void main() {
+    vec4 pp = data[gl_VertexID / 18].pospos;
+    int j = indices[gl_VertexID % 18];
+    vec2 xy = (j % 2 > 0 ? pp.xy : pp.zw);
+    float z = ((j / 2) % 2 > 0.5 ? 100 : -500);
+    vec2 xyo = ( j > 3.5 ? shift(xy) : xy);
+    vec4 p = theMat * vec4(xyo,z,1);
+    gl_Position = (isLHS(pp.xy-lightPos.xy,pp.zw-lightPos.xy) < 0 
+            ? p
+            : vec4(1,1,1,0));
 }