// motion blur neighborhood max pass

// noisiness
#define JITTER_SCALE (0.275f)
// 's' in paper (# of samples for reconstruction)
#define NUM_SAMPLES (13)
// # samples for valve style blur
#define MOTION_SAMPLES (16)
// 'k' in paper
// (make sure to match this to MAX_RADIUS in script)    
#define MAX_RADIUS (8)

struct v2f {
    float4 pos : POSITION;
    float2 uv  : TEXCOORD0;
};
            
sampler2D _MainTex;
float4 _MainTex_TexelSize;

float2 maxMag(float2 a, float2 b)
{
    float ma = dot(a, a);
    float mb = dot(b, b);
    return lerp(a, b, step(ma,mb));
}

// find maximum velocity in any adjacent tile
float4 main(v2f i) : COLOR
{
    float2 mx = tex2D(_MainTex, i.uv).xy;
    for(int j = -1; j<2; j++) {
        for(int l = -1; l<2; l++) {
            float2 v = tex2D(_MainTex, i.uv + float2(l,j) * _MainTex_TexelSize.xy).xy;
            mx = maxMag(mx, v);
        }
    }
    return float4(mx, 0, 0);        
}