Move towards geometry instancing for shadows

shader/shadow/cap.geom

@@ -0,0 +1,42 @@
+#version 450 core
+layout (triangles) in;
+layout (triangle_strip, max_vertices = 3) out;
+layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
+//layout (std140, binding = 1) uniform LightsBlock
+//{
+//    vec4 posBool[20];
+//    vec4 colRad[20];
+//} ;
+uniform vec3 lightPos;
+uniform int lightID;
+// this code is duplicated in lineShadow.geom, should not be changed on its own
+vec4 projNear (vec4 pos)
+{
+    // note we project to a specific height
+    // this is quite brittle, not ideal
+    vec3 dir = pos.xyz - lightPos ;
+    float a = (140 - pos.z) / dir.z ;
+    vec2 xy = (pos.xyz + a * dir).xy ;
+    return vec4 ( xy, 140 , 1) ;
+}
+void main()
+{
+    vec4 p0 = gl_in[0].gl_Position ;
+    vec4 p1 = gl_in[1].gl_Position ;
+    vec4 p2 = gl_in[2].gl_Position ;
+    if ( //if Light Source is below all vertices, draw cap 
+        // TODO think about when LS is beside the object
+            ( p0.z - lightPos.z > 0 )
+            && ( p1.z - lightPos.z > 0 )
+            && ( p2.z - lightPos.z > 0 )
+            )
+    {
+        // the front cap
+        vec4 v1 = vec4 (0,0,1,0) ;
+        gl_Position = theMat * projNear(p0); EmitVertex();
+        gl_Position = theMat * projNear(p1); EmitVertex();
+        gl_Position = theMat * projNear(p2); EmitVertex();
+        EndPrimitive();
+    }
+    else {}
+}