// Heartfelt - by Martijn Steinrucken aka BigWings - 2017
// Email:countfrolic@gmail.com Twitter:@The_ArtOfCode
// License Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

// I revisited the rain effect I did for another shader. This one is better in multiple ways:
// 1. The glass gets foggy.
// 2. Drops cut trails in the fog on the glass.
// 3. The amount of rain is adjustable (with Mouse.y)

// To have full control over the rain, uncomment the HAS_HEART define 

// A video of the effect can be found here:
// https://www.youtube.com/watch?v=uiF5Tlw22PI&feature=youtu.be

// Music - Alone In The Dark - Vadim Kiselev
// https://soundcloud.com/ahmed-gado-1/sad-piano-alone-in-the-dark
// Rain sounds:

// https://soundcloud.com/elirtmusic/sleeping-sound-rain-and-thunder-1-hours

#ifdef GL_ES
precision mediump float;
#endif
uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;
//uniform sampler2D iChannel0;
uniform sampler2D u_texture_0;
#define S(a, b, t) smoothstep(a, b, t)
//#define CHEAP_NORMALS
//#define HAS_HEART
#define USE_POST_PROCESSING

vec3 N13(float p) {
    //  from DAVE HOSKINS
   vec3 p3 = fract(vec3(p) * vec3(.1031,.11369,.13787));
   p3 += dot(p3, p3.yzx + 19.19);
   return fract(vec3((p3.x + p3.y)*p3.z, (p3.x+p3.z)*p3.y, (p3.y+p3.z)*p3.x));
}

vec4 N14(float t) {
	return fract(sin(t*vec4(123., 1024., 1456., 264.))*vec4(6547., 345., 8799., 1564.));
}
float N(float t) {
    return fract(sin(t*12345.564)*7658.76);
}

float Saw(float b, float t) {
	return S(0., b, t)*S(1., b, t);
}


vec2 DropLayer2(vec2 uv, float t) {
    vec2 UV = uv;
    
    uv.y += t*0.75;
    vec2 a = vec2(6., 1.);
    vec2 grid = a*2.;
    vec2 id = floor(uv*grid);
    
    float colShift = N(id.x); 
    uv.y += colShift;
    
    id = floor(uv*grid);
    vec3 n = N13(id.x*35.2+id.y*2376.1);
    vec2 st = fract(uv*grid)-vec2(.5, 0);
    
    float x = n.x-.5;
    
    float y = UV.y*20.;
    float wiggle = sin(y+sin(y));
    x += wiggle*(.5-abs(x))*(n.z-.5);
    x *= .7;
    float ti = fract(t+n.z);
    y = (Saw(.85, ti)-.5)*.9+.5;
    vec2 p = vec2(x, y);
    
    float d = length((st-p)*a.yx);
    
    float mainDrop = S(.4, .0, d);
    
    float r = sqrt(S(1., y, st.y));
    float cd = abs(st.x-x);
    float trail = S(.23*r, .15*r*r, cd);
    float trailFront = S(-.02, .02, st.y-y);
    trail *= trailFront*r*r;
    
    y = UV.y;
    float trail2 = S(.2*r, .0, cd);
    float droplets = max(0., (sin(y*(1.-y)*120.)-st.y))*trail2*trailFront*n.z;
    y = fract(y*10.)+(st.y-.5);
    float dd = length(st-vec2(x, y));
    droplets = S(.3, 0., dd);
    float m = mainDrop+droplets*r*trailFront;
    
    //m += st.x>a.y*.45 || st.y>a.x*.165 ? 1.2 : 0.;
    return vec2(m, trail);
}

float StaticDrops(vec2 uv, float t) {
	uv *= 40.;
    
    vec2 id = floor(uv);
    uv = fract(uv)-.5;
    vec3 n = N13(id.x*107.45+id.y*3543.654);
    vec2 p = (n.xy-.5)*.7;
    float d = length(uv-p);
    
    float fade = Saw(.025, fract(t+n.z));
    float c = S(.3, 0., d)*fract(n.z*10.)*fade;
    return c;
}

vec2 Drops(vec2 uv, float t, float l0, float l1, float l2) {
    float s = StaticDrops(uv, t)*l0; 
    vec2 m1 = DropLayer2(uv, t)*l1;
    vec2 m2 = DropLayer2(uv*1.85, t)*l2;
    
    float c = s+m1.x+m2.x;
    c = S(.3, 1., c);
    
    return vec2(c, max(m1.y*l0, m2.y*l1));
}

void main()
{
	vec2 uv = (gl_FragCoord.xy-.5*u_resolution.xy) / u_resolution.y;
    vec2 UV = gl_FragCoord.xy/u_resolution.xy;
    //vec2 st =gl_FragCoord.xy/u_resolution.xy;
    vec2 M = u_mouse.xy/u_resolution.xy;
    float T = u_time+M.x*2.;
    
    #ifdef HAS_HEART
    T = mod(u_time, 102.);
    T = mix(T, M.x*102., M.y>0.?1.:0.);
    #endif
    
    
    float t = T*.2;
    
    float rainAmount = u_mouse.y>0. ? M.y : sin(T*.05)*.3+.7;
    
    float maxBlur = mix(3., 6., rainAmount);
    float minBlur = 2.;
    
    float story = 0.;
    float heart = 1.;
    
    #ifdef HAS_HEART
    story = S(0., 70., T);
    
    t = min(1., T/70.);						// remap drop time so it goes slower when it freezes
    t = 1.-t;
    t = (1.-t*t)*70.;
    
    float zoom= mix(.3, 1.2, story);		// slowly zoom out
    uv *=zoom;
    minBlur = 4.+S(.5, 1., story)*3.;		// more opaque glass towards the end
    maxBlur = 6.+S(.5, 1., story)*1.5;
    
    vec2 hv = uv-vec2(.0, -.1);				// build heart
    hv.x *= .5;
    float s = S(110., 70., T);				// heart gets smaller and fades towards the end
    hv.y-=sqrt(abs(hv.x))*.5*s;
    heart = length(hv);
    heart = S(.4*s, .2*s, heart)*s;
    rainAmount = heart;						// the rain is where the heart is
    
    maxBlur-=heart;							// inside the heart slighly less foggy
    uv *= 1.5;								// zoom out a bit more
    t *= .25;
    #else
    //float zoom = -cos(T*.2);
    //uv *= .7+zoom*.3;
    #endif
  //  UV = (UV-.5)*(.9+zoom*.1)+.5;
    
    float staticDrops = S(-.5, 1., rainAmount)*2.;
    float layer1 = S(.25, .75, rainAmount);
    float layer2 = S(.0, .5, rainAmount);
    
    
    vec2 c = Drops(uv, t, staticDrops, layer1, layer2);
   #ifdef CHEAP_NORMALS
    	vec2 n = vec2(dFdx(c.x), dFdy(c.x));// cheap normals (3x cheaper, but 2 times shittier ;))
    #else
    	vec2 e = vec2(.001, 0.);
    	float cx = Drops(uv+e, t, staticDrops, layer1, layer2).x;
    	float cy = Drops(uv+e.yx, t, staticDrops, layer1, layer2).x;
    	vec2 n = vec2(cx-c.x, cy-c.x);		// expensive normals
    #endif
    
    
    #ifdef HAS_HEART
    n *= 1.-S(60., 85., T);
    c.y *= 1.-S(80., 100., T)*.8;
    #endif
    
    float focus = mix(maxBlur-c.y, minBlur, S(.1, .2, c.x));  
    vec3 col =texture2D(u_texture_0 ,UV+n*u_time).rgb;
    
    
   
    //col = vec3(heart);
    gl_FragColor = vec4(col, 1.);
}