// Each #kernel tells which function to compile; you can have many kernels
#pragma kernel CSMain

// Create a RenderTexture with enableRandomWrite flag and set it
// with cs.SetTexture
RWStructuredBuffer<float> oldVegetation;
RWStructuredBuffer<float> vegetation;
RWStructuredBuffer<float> oldWater;
RWStructuredBuffer<float> water;
RWStructuredBuffer<float> feedModifier;
RWStructuredBuffer<float> killModifier;
int sizeX;
int sizeY;

float DWater;
float DVegetation;
float feedRate;
float killRate;
float dT;

int index(int x, int y)
{
    return x + sizeX * y;
}

float get(RWStructuredBuffer<float> array, int x, int y)
{
    int idx = index(x, y);
    if (idx < 0 || idx >= sizeX * sizeY)
    {
        return 0;
    }

    return array[idx];
}

float laplace(RWStructuredBuffer<float> array, int x, int y)
{
    return 0.2 * (get(array, x + 1, y) + get(array, x - 1, y) + get(array, x, y + 1) + get(array, x, y - 1))
        + 0.05 * (get(array, x + 1, y + 1) + get(array, x + 1, y - 1) + get(array, x - 1, y + 1) + get(array, x - 1, y - 1))
        - get(array, x, y);
}

[numthreads(8,8,1)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
    int x = id.x;
    int y = id.y;

    float w = oldWater[index(x, y)];
    float r = oldVegetation[index(x, y)];

    float feed = feedRate * feedModifier[index(x, y)];
    float kill = killRate * killModifier[index(x, y)];

    water[index(x, y)] = clamp(w + dT * DWater * laplace(oldWater, x, y) - w * w * r * r + feed, 1, 0);
    vegetation[index(x, y)] = clamp(r + dT * (DVegetation * laplace(oldVegetation, x, y) + r * (w * r - kill)), 1, 0);
}