#version 450 core
struct DataS { vec2 pos; vec2 v1; vec2 v2; vec2 t1; vec2 t2; vec2 t3; };
layout (std430, binding = 9) readonly buffer Data { DataS data[]; };
layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
out vec2 texPos;
out vec2 distmask;
out vec2 pinch;
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)
    };
vec2 f (vec2 p) // transforms a vector from "world" into "screen" space
{ return (theMat * vec4(p,0,1) - theMat * vec4(0,0,0,1)).xy; }
vec2 g (vec2 p)
{ return normalize(p); }
vec2 ncToTex (vec2 p) {return 0.5 * (p + 1);}
mat4 toTransMat (vec2 p)
{ return mat4
    (  1,  0, 0 ,0
    ,  0,  1, 0 ,0
    ,  0,  0, 1 ,0
    ,p.x,p.y, 0 ,1
    ) ;
}
void main()
{
  int k = ks[gl_VertexID];
  DataS thedata = data[gl_VertexID/6];
  vec4 off = theMat * vec4(data[gl_VertexID/6].pos, 0,1);
  vec2 r1 = f(thedata.v1);
  vec2 r2 = f(thedata.v2);
  mat2 distT = inverse (mat2(r1,r2));
  distmask = distT * (cs[k] - off.xy);
  vec4 pinchx = theMat 
      * toTransMat(thedata.t3) 
      * toTransMat(thedata.pos)
      * mat4
        (thedata.t1 , 0, 0
        ,thedata.t2 , 0, 0
        , 0,      0 , 0, 0
        , 0,      0 , 0, 1
        )
      * inverse(toTransMat(thedata.pos))
      * inverse(theMat) 
      * (vec4(cs[k],0,1));
  pinch = ncToTex(pinchx.xy) - ncToTex(cs[k]);
  texPos = ncToTex(cs[k]);
  gl_Position = vec4 (cs[k],0,1);
}