// Stylized Water 3 by Staggart Creations (http://staggart.xyz)
// COPYRIGHT PROTECTED UNDER THE UNITY ASSET STORE EULA (https://unity.com/legal/as-terms)
//    • Copying or referencing source code for the production of new asset store, or public, content is strictly prohibited!
//    • Uploading this file to a public repository will subject it to an automated DMCA takedown request.

#pragma kernel CSMain

Texture2D<float4> _InputTexture;
RWTexture2D<float> _OutputTexture;

float _MaxDistance;

uint2 _TextureSize;

[numthreads(8, 8, 1)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
    if (id.x >= _TextureSize.x || id.y >= _TextureSize.y) return;

    float pixel = _InputTexture[id.xy].r;
    bool isBackground = pixel.r > 0.5; //Assume white is the background

    float minDistance = _MaxDistance;
    
    //Reduced search window based on _MaxDistance
    int searchRadius = int(_MaxDistance);
    int2 start = max(int2(0, 0), int2(id.xy) - searchRadius);
    int2 end = min(_TextureSize, int2(id.xy) + searchRadius + 1);
    
    for (int y = start.y; y < end.y; y++)
    {
        for (int x = start.x; x < end.x; x++)
        {
            float sample = _InputTexture[int2(x, y)].r;
            bool sampleIsBackground = sample.r > 0.5;

            if(sampleIsBackground == isBackground || sample < pixel) continue;
            //if (sampleIsBackground != isBackground && sample > pixel)
            {
                float2 diff = float2(x, y) - id.xy;
                float distance = length(diff);
                if (distance < minDistance)
                {
                    minDistance = distance;
                }
            }
        }
    }

    _OutputTexture[id.xy] = 1-(minDistance / _MaxDistance); // Normalize
}