#version 430 core

struct cell_t {
    float pheromone;
    float result;
    int population;
};

uniform uint map_width;
uniform uint map_height;

uniform float increase;
uniform float decay;
uniform float diffusion;

uniform float dt;

layout(std430, binding = 2) coherent buffer map_buffer
{
    cell_t map[];
};

uint cell_id(int x, int y){
    return uint(mod(y, map_height) * map_width + mod(x, map_width));
}

layout(local_size_x = 16, local_size_y = 16, local_size_z = 1) in;
void main(){
    int x = int(gl_GlobalInvocationID.x);
    int y = int(gl_GlobalInvocationID.y);

    if(x >= map_width || y >= map_height){
        return;
    }

    float frac = diffusion * dt;
    float val = map[cell_id(x,y)].pheromone + map[cell_id(x,y)].population * increase * dt;
    val = val * (1 - 4 * frac) 
        + (map[cell_id(x-1,y)].pheromone
        +  map[cell_id(x+1,y)].pheromone
        +  map[cell_id(x,y-1)].pheromone
        +  map[cell_id(x,y+1)].pheromone) * frac;
    val = val * exp(-decay * dt);

    map[cell_id(x,y)].result = val;
}