// perlin — generated from https://github.com/gl-transitions/gl-transitions/blob/master/transitions/perlin.glsl
// Author: Rich Harris
// License: MIT
// Description: The incoming image appears through blobs of Perlin noise

uniform shader _from;
uniform shader _to;
uniform float2 _resolution;
uniform float progress;
uniform float ratio;

vec4 getFromColor(vec2 uv) { return vec4(unpremul(_from.eval(vec2(uv.x, 1.0 - uv.y) * _resolution))); }
vec4 getToColor(vec2 uv) { return vec4(unpremul(_to.eval(vec2(uv.x, 1.0 - uv.y) * _resolution))); }

uniform float scale; 

uniform float smoothness; 

uniform float seed; 

float random(vec2 co)
{
    float a = seed;
    float b = 78.233;
    float c = 43758.5453;
    float dt= dot(co.xy ,vec2(a,b));
    float sn= mod(dt,3.14);
    return fract(sin(sn) * c);
}

float noise (in vec2 st) {
    vec2 i = floor(st);
    vec2 f = fract(st);

    
    float a = random(i);
    float b = random(i + vec2(1.0, 0.0));
    float c = random(i + vec2(0.0, 1.0));
    float d = random(i + vec2(1.0, 1.0));

    

    
    vec2 u = f*f*(3.0-2.0*f);
    

    
    return mix(a, b, u.x) +
            (c - a)* u.y * (1.0 - u.x) +
            (d - b) * u.x * u.y;
}

vec4 transition (vec2 uv) {
  vec4 from = getFromColor(uv);
  vec4 to = getToColor(uv);
  float n = noise(uv * scale);

  float p = mix(-smoothness, 1.0 + smoothness, progress);
  float lower = p - smoothness;
  float higher = p + smoothness;

  float q = smoothstep(lower, higher, n);

  return mix(
    from,
    to,
    1.0 - q
  );
}

half4 main(float2 _coord) {
  vec2 _uv = _coord / _resolution;
  vec4 _c = clamp(transition(vec2(_uv.x, 1.0 - _uv.y)), 0.0, 1.0);
  return half4(_c.rgb * _c.a, _c.a);
}