Work towards using vertex pulling for lighting caps, alignment issues

shader/lighting/cap.vert

@@ -1,11 +1,48 @@
 #version 450 core
-layout (location = 0) in vec4 position;
+struct PosColNorm { vec4 pos; vec4 col; vec4 norm; };
 layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
-uniform vec3 lightPos;
-uniform vec4 lumRad;
-out float drawbit;
-void main()
+layout (std430, binding = 3) readonly buffer Data { PosColNorm data[]; };
+layout (std430, binding = 4) readonly buffer Indices { uint indices[]; };
+layout(location=0)uniform vec3 lightPos;
+layout(location=1)uniform vec4 lumRad;
+vec4 projNear (vec4 pos)
 {
-    gl_Position = vec4(position.xyz,1);
-    drawbit = position.w;
+    // note we project to a specific height
+    // this is quite brittle, not ideal
+    vec3 dir = pos.xyz - lightPos ;
+    float a = (100 - pos.z) / dir.z ;
+    vec2 xy = (pos.xyz + a * dir).xy ;
+    return vec4 ( xy, 100 , 1) ;
 }
+vec4 tris[3] =
+    {vec4(0,0,0,1)
+    ,vec4(1,1,0,1)
+    ,vec4(0,1,0,1)
+    };
+bool ztest (vec4 p) {return p.z - lightPos.z > 0;}
+void main() {
+    int j = gl_VertexID/3;
+    int i1 = j * 3;
+    uint t = indices[gl_VertexID];
+    //uint t = gl_VertexID;
+    gl_Position = tris[t];
+    //uint t = gl_VertexID % 3;
+    vec4 p = data[indices[gl_VertexID]].pos;
+//    gl_Position = (p.w == 1
+//            && ztest(data[indices[i1]].pos)
+//            && ztest(data[indices[i1+1]].pos)
+//            && ztest(data[indices[i1+2]].pos)
+//            ? theMat * projNear(p)
+//            : vec4(1,1,1,0)
+//            );
+}
+//layout (location = 0) in vec4 position;
+//layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
+//uniform vec3 lightPos;
+//uniform vec4 lumRad;
+//out float drawbit;
+//void main()
+//{
+//    gl_Position = vec4(position.xyz,1);
+//    drawbit = position.w;
+//}

shader/lighting/wallShadow.vert

@@ -1,9 +1,4 @@
 #version 450 core
-//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[]; };