#version 330
in vec2 TexCoord;

layout(location = 0) out vec4 OutAlbedo;
layout(location = 1) out vec4 OutWorldPosSpecularity;
layout(location = 2) out vec4 OutNormalBooleans;

uniform sampler2D Depth;
uniform sampler2D Albedo;
uniform sampler2D Position;
uniform sampler2D Normal;
uniform sampler2D Wind;

uniform mat4 ViewMatrix;
uniform mat4 ProjectionMatrix;
uniform vec3 CameraPosition;
uniform float Time;

vec3 permute(vec3 x) { return mod(((x*34.0)+1.0)*x, 289.0); }

float snoise(vec2 v){
  const vec4 C = vec4(0.211324865405187, 0.366025403784439,
           -0.577350269189626, 0.024390243902439);
  vec2 i  = floor(v + dot(v, C.yy) );
  vec2 x0 = v -   i + dot(i, C.xx);
  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;
  i = mod(i, 289.0);
  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 ;
  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;
  m *= 1.79284291400159 - 0.85373472095314 * ( a0*a0 + h*h );
  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);
}

void GetStates(float Factor, out bool ShadowCatcher, out bool GrassField) {
    ShadowCatcher = (Factor > 0.01 && Factor < 0.51);
    GrassField = (Factor > 0.49);
}

void main() {

    bool IsShadowCatcher, IsGrassField;
    vec4 SampleNormal = texture(Normal, TexCoord);
    vec4 SampleWorldPosition = texture(Position, TexCoord);
    vec4 SampleAlbedo = texture(Albedo, TexCoord);
    GetStates(SampleNormal.a, IsShadowCatcher, IsGrassField);

    vec2 TextureSize = vec2(textureSize(Position, 0));
    vec2 TexelSize = 1.0 / TextureSize;

    float CurrentDistance = 10000.0;
    float GrassHeight = 0.;



    vec2 SWING = vec2(0.01, -0.01);

    if(SampleWorldPosition.a > -0.1) {

    vec3 Up = vec3(vec4(SampleWorldPosition.xyz, 1.0) * inverse(transpose(ViewMatrix)));
    vec3 Down = Up - vec3(0.,0.05,0.);

    vec4 NDCUp = ProjectionMatrix * ViewMatrix * vec4(Up,1.);
    vec2 TCUp = (NDCUp.xy / NDCUp.w) * 0.5 + 0.5;

    vec4 NDCDown = ProjectionMatrix * ViewMatrix * vec4(Down,1.);
    vec2 TCDown = (NDCDown.xy / NDCDown.w) * 0.5 + 0.5;


    int StepCount = int(distance(TCDown * TextureSize, TCUp * TextureSize));

    vec2 Direction = normalize(TCDown - TCUp);

    vec3 GrassWorldPosition = vec3(-1.);

    vec3 OneStepInWorldSpace = vec3(0.,0.05, 0.) / vec3(max(StepCount, 1));

    int Steps = 0;

    float GrassHeight;

    vec3 WorldPosGrassBottom;
    vec3 ActualWorldPosGrassBottom;
    bool Hit = false;

    for(int i=0;i<min(max(StepCount,1), 200);i++) {

        vec4 Sample = texture(Position, TexCoord + vec2(Direction * vec2(i)) * TexelSize);

        vec4 SampleNormal = texture(Normal, TexCoord + vec2(Direction * vec2(i)) * TexelSize);

        WorldPosGrassBottom = vec3(vec4(Sample.xyz, 1.0) * inverse(transpose(ViewMatrix)));



        float Distance = distance(CameraPosition, WorldPosGrassBottom);

        vec3 Seed = fract(floor(WorldPosGrassBottom * 1000.0) / 1000.0);

        vec3 WindSample = texture(Wind, WorldPosGrassBottom.xz + vec2(Time * 0.05, -Time * 0.04)).xyz;

        vec2 Wind = ((WindSample.xy * 2. - 1.) * (1.-WindSample.z) * 4.0) * vec2(float(i)/float(max(StepCount,1)));



        if(pow(snoise(Seed.xz * 100.0 + Wind) ,0.5) > 0.85 * pow(1.-min(Distance * .01,1.), 10.0) && SampleNormal.a > 0.49) {

        Hit = true;
        GrassHeight = (Distance > 0. && Distance < CurrentDistance) ? 1. : GrassHeight;
        CurrentDistance = (Distance > 0. && Distance < CurrentDistance) ? Distance : CurrentDistance;
        GrassWorldPosition = (Distance > 0. && Distance < CurrentDistance) ? GrassWorldPosition : (WorldPosGrassBottom - (OneStepInWorldSpace * vec3(-i)));
        GrassHeight = (Distance > 0. && Distance < CurrentDistance) ? GrassHeight : -(OneStepInWorldSpace.y * float(-i));
        ActualWorldPosGrassBottom = (Distance > 0. && Distance < CurrentDistance) ? ActualWorldPosGrassBottom : WorldPosGrassBottom + (vec3(Wind.x,0.,Wind.y) / vec3(100.));
        Steps = i;

        }
    }

    vec3 GrassNormal = vec3(0.,1.,0.);

    //Get The Grass Depth =

    vec4 ClipSpace = ProjectionMatrix * ViewMatrix * vec4(GrassWorldPosition, 1.0);
    vec4 NDCSpace = ClipSpace / ClipSpace.w;

    float GrassDepth = NDCSpace.z * .5 + .5;
    float DefferedDepth = texture(Depth,TexCoord).x;


    vec4 ClipSpaceGrassBottom = ProjectionMatrix * ViewMatrix * vec4(ActualWorldPosGrassBottom, 1.0);
    vec4 NDCSpaceGrassBottom = ClipSpaceGrassBottom / ClipSpaceGrassBottom.w;

    vec4 GrassBottomNormal = texture(Normal, NDCSpaceGrassBottom.xy*.5+.5);


    if(GrassDepth < DefferedDepth && Hit && GrassBottomNormal.a > 0.49) {

    gl_FragDepth = GrassDepth;

    float MixFactor = min(GrassHeight * 5., 1.0);

    OutAlbedo.xyz = texture(Albedo, NDCSpaceGrassBottom.xy*.5+.5).xyz * (GrassHeight*10.);
    //OutAlbedo.xyz = max(OutAlbedo.xyz, vec3(1.));
    OutAlbedo.a = 1.0;
    OutWorldPosSpecularity = vec4(vec3(ViewMatrix * vec4(GrassWorldPosition,1.)), 0.);
    OutNormalBooleans = vec4(GrassNormal, 0.);

    }
    else {
    gl_FragDepth = DefferedDepth;
    OutAlbedo = SampleAlbedo;
    OutWorldPosSpecularity = SampleWorldPosition;
    OutNormalBooleans = SampleNormal;
    }


    }
    else {
    gl_FragDepth = texture(Depth,TexCoord).x;
    OutAlbedo = SampleAlbedo;
    OutWorldPosSpecularity = SampleWorldPosition;
    OutNormalBooleans = SampleNormal;
    }
}