#version 450 core
struct PosColNorm { vec4 pos; vec4 dummy; };
layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
layout (std430, binding = 3) readonly buffer Data { PosColNorm data[]; };
layout (std430, binding = 4) readonly buffer Indices { uint indices[]; };
layout(location=0)uniform vec3 lightPos;
layout(location=1)uniform vec4 lumRad;
vec4 projNear (vec4 pos)
{
    // note we project to a specific height
    // this is quite brittle, not ideal
    vec3 dir = pos.xyz - lightPos ;
    float a = (100 - pos.z) / dir.z ;
    vec2 xy = (pos.xyz + a * dir).xy ;
    return vec4 ( xy, 100 , 1) ;
}
bool ztest (vec4 p) {return p.z - lightPos.z > 0;}
void main() {
    int j = gl_VertexID/3;
    int i1 = j * 3;
    vec4 po = data[indices[gl_VertexID]].pos;
    gl_Position = (po.w == 1
            && ztest(data[indices[i1]].pos)
            && ztest(data[indices[i1+1]].pos)
            && ztest(data[indices[i1+2]].pos)
            ? theMat * projNear(po)
            : vec4(1,1,1,0)
            );
}
//layout (location = 0) in vec4 position;
//layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
//uniform vec3 lightPos;
//uniform vec4 lumRad;
//out float drawbit;
//void main()
//{
//    gl_Position = vec4(position.xyz,1);
//    drawbit = position.w;
//}