vec2 mod289(vec2 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
vec3 mod289(vec3 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
vec4 mod289(vec4 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }
vec3 permute(vec3 x) { return mod289(((x*34.0)+1.0)*x); }
vec4 permute(vec4 x) { return mod289(((x*34.0)+1.0)*x); }

/// <summary>
/// 2D Noise by Ian McEwan, Ashima Arts.
/// <summary>
float snoise_2D (vec2 v)
{
    const vec4 C = vec4(0.211324865405187,  // (3.0-sqrt(3.0))/6.0
                        0.366025403784439,  // 0.5*(sqrt(3.0)-1.0)
                        -0.577350269189626, // -1.0 + 2.0 * C.x
                        0.024390243902439); // 1.0 / 41.0

    // First corner
    vec2 i  = floor(v + dot(v, C.yy) );
    vec2 x0 = v -   i + dot(i, C.xx);

    // Other corners
    vec2 i1;
    i1 = (x0.x > x0.y) ? vec2(1.0, 0.0) : vec2(0.0, 1.0);
    vec4 x12 = x0.xyxy + C.xxzz;
    x12.xy -= i1;

    // Permutations
    i = mod289(i); // Avoid truncation effects in permutation
    vec3 p = permute( permute( i.y + vec3(0.0, i1.y, 1.0 ))
        + i.x + vec3(0.0, i1.x, 1.0 ));

    vec3 m = max(0.5 - vec3(dot(x0,x0), dot(x12.xy,x12.xy), dot(x12.zw,x12.zw)), 0.0);
    m = m*m ;
    m = m*m ;

    // Gradients: 41 points uniformly over a line, mapped onto a diamond.
    // The ring size 17*17 = 289 is close to a multiple of 41 (41*7 = 287)

    vec3 x = 2.0 * fract(p * C.www) - 1.0;
    vec3 h = abs(x) - 0.5;
    vec3 ox = floor(x + 0.5);
    vec3 a0 = x - ox;

    // Normalise gradients implicitly by scaling m
    // Approximation of: m *= inversesqrt( a0*a0 + h*h );
    m *= 1.79284291400159 - 0.85373472095314 * ( a0*a0 + h*h );

    // Compute final noise value at P
    vec3 g;
    g.x  = a0.x  * x0.x  + h.x  * x0.y;
    g.yz = a0.yz * x12.xz + h.yz * x12.yw;
    return 130.0 * dot(m, g);
}
//DEBUG
#define DROPS_TURBSIZE 15.f
#define DROPS_TURBSHIFT vec4(0.35, 1, 0, 1)
#define DROPS_TURBTIME sin(0.1/3.f)
#define DROPS_TURBCOF 0.33


vec2 l_jh2(vec2 f, vec4 s, float l)
{
	vec2 x = s.xy, V = s.zw;
	float y = snoise_2D(f * vec2(DROPS_TURBSIZE, DROPS_TURBSIZE))*.5;
	vec4 r = vec4(y, y, y, 1);
	r.xy = vec2(r.x + r.z/4.f, r.y + r.x/2.f);
	r -= 1.5;
	r *= l;
	return (f + (x + V) *r.xy);
}

















float noise(float t)
{
    return fract(sin(t*10.0)*10.0);
}

float noise2(vec2 p)
{
    return noise(p.x + noise(p.y));
}

float raindot(vec2 uv, vec2 id, float t)
{
    vec2 p = 0.25 + 0.25 * vec2(noise2(id), noise2(id + vec2(1.0, 0.0)));
    float r = clamp(0.5 - mod(t + noise2(id), 1.0), 0.0, 1.0);
    return smoothstep(0.3 * r, 0.0, length(p - uv));
}

/////////////////////////////////////////////////////////////////////////////
//rain pass
#define r_size 5.f //raindrops size
#define r_intensity 1.0

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
//clean img and coords
    vec4 final;
	vec2 uv = fragCoord.xy / iResolution.xy;

    final = texture( iChannel0, uv);

//rain pass
    float v = raindot(fract(mix(uv, l_jh2(uv, DROPS_TURBSHIFT, DROPS_TURBTIME), DROPS_TURBCOF) * r_size + vec2(0, 0.1 * iTime)), floor(uv * r_size + vec2(0, 0.1 * iTime)), iTime);
    vec2 rain = vec2(vec2(dFdx(v*0.5f), dFdy(v*0.5f))  / (v + r_size))*r_intensity;
	vec4 mask_rain = texture(iChannel0, uv+rain);


/////////////////////////////////////////////////////////////////////////////
//final combine

	final = mask_rain;
    fragColor = final;
}