Work on distortion shader

shader/texture/barrel.vert

@@ -1,18 +1,27 @@
 #version 450 core
-layout (location = 0) in vec2 pos;
-layout (location = 1) in vec2 rad1;
-layout (location = 2) in vec2 rad2;
-layout (location = 3) in float factor;
+struct DataS { vec2 pos; vec2 rad1; vec2 rad2; };
+layout (std430, binding = 9) readonly buffer Data { DataS data[]; };
 layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
-out vec2 vCen;
-out vec2 vRad1;
-out vec2 vRad2;
-out float vFactor;
+out vec2 texPos;
+out vec2 distmask;
+const int ks[6] =   
+    {0,1,2          //  2--3
+    ,2,1,3          //  |  |
+    };              //  0--1
+const vec2 cs[4] =
+    { vec2 (-1,-1)
+    , vec2 ( 1,-1)
+    , vec2 (-1, 1)
+    , vec2 ( 1, 1)
+    };
 void main()
 {
-  gl_Position = vec4(0,0,0,1);
-  vCen = (theMat * vec4(pos,0,1)).xy;
-  vRad1 = (theMat * vec4(rad1,0,1)).xy;
-  vRad2 = (theMat * vec4(rad2,0,1)).xy;
-  vFactor = factor;
+  int k = ks[gl_VertexID];
+  vec4 off = (theMat * vec4(data[gl_VertexID/6].pos, 0,1));
+  float r = distance
+        ((theMat * vec4(data[gl_VertexID/6].rad1, 0,1)).xy
+        ,(theMat * vec4(0,0, 0,1)).xy);
+  distmask = (cs[k] - off.xy)/r;
+  texPos = 0.5 * (cs[k]+vec2(1,1));
+  gl_Position = vec4 (cs[k],0,1);
 }