#version 450 core
struct PosCol { vec4 posx; vec4 colx; };
layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
layout (std430, binding = 13) readonly buffer Data { PosCol data[]; };
layout (location = 0) uniform int n;
out vec4 gColC; // center color
out vec4 gColE; // edge color
out vec2 gBoundingBox;
out vec3 gPos;
const int ks[6] = //    
    {1,0,2  //  2--3    
    ,2,0,3  //  |  |    
    };      //  1--0    
            //          
const vec2 bs[4] =
    { vec2( 1, 1)
    , vec2(-1, 1)
    , vec2(-1,-1)
    , vec2( 1,-1)
    } ;
void main()
{
    int i0 = n + (3 * ((gl_VertexID-n)/6) );
    gColC = data[i0].colx;
    gColE = data[i0+1].colx;
    int k = ks[(gl_VertexID - n) % 6];
    gBoundingBox = bs[k];
    gPos = (k > 2.5 
            ? data[i0].posx + data[i0+2].posx - data[i0+1].posx
            : data[i0+k].posx
           ).xyz;
  gl_Position = theMat * vec4(gPos,1);
}