Add barrel distortion shader

shader/background.geom

@@ -1,15 +1,36 @@
 #version 430 core
 layout (points) in;
 layout (triangle_strip, max_vertices = 4) out;
-void main()
-{
-  gl_Position = vec4 (1,1,0.9,1);
+in vec2 vRad1;
+in vec2 vRad2;
+in float vFactor;
+out vec2 cenPos;
+out vec2 texPos;
+out vec2 texDist;
+out float factor;
+const float root = 1 / sqrt(2) ;
+void main() {
+  factor = vFactor[0];
+  rad1 = vRad1[0];
+  rad2 = vRad2[0];
+  cenPos = gl_in[0].gl_Position;
+  vec2 g (vec2 p) { return vec2(dot(rad1,p), dot(rad2,p)); }
+
+  texPos = vec2(1,1);
+  texDist = g(root,root);
+  gl_Position = vec4 (1,1,0,1);
   EmitVertex();
-  gl_Position = vec4 (1,-1,0.9,1);
+  texPos = vec2(1,0);
+  texDist = g(root,-root);
+  gl_Position = vec4 (1,-1,0,1);
   EmitVertex();
-  gl_Position = vec4 (-1,1,0.9,1);
+  texPos = vec2(0,1);
+  texDist = g(-root,root);
+  gl_Position = vec4 (-1,1,0,1);
   EmitVertex();
-  gl_Position = vec4 (-1,-1,0.9,1);
+  texPos = vec2(0,0);
+  texDist = g(-root,-root);
+  gl_Position = vec4 (-1,-1,0,1);
   EmitVertex();
   EndPrimitive();
 }