#version 450

#define INDEX(_x, _y) ((_y) * WIDTH + (_x))
#define IS_CONNECTED(_i0, _i1) (values[_i0] >= 0 && values[_i1] >= 0)
#define LABEL(_idx) (values[_idx])

layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
layout(constant_id = 0) const uint WIDTH = 8;
layout(constant_id = 1) const uint HEIGHT = 8;
layout(binding = 0) buffer Binding { 
    int values[];
};

void scanColumn(uint x) {
    for (uint y = 1; y < HEIGHT; ++y) {
        uint i0 = INDEX(x, y-1);
        uint i1 = INDEX(x, y);
        if (IS_CONNECTED(i0, i1)) {
            LABEL(i1) = LABEL(i0);
        }
    }
}

void main() {
    uint id = gl_GlobalInvocationID.x;
    scanColumn(id);
}