// Copyright (c) 2017-2018 Xiamen Yaji Software Co., Ltd.

CCEffect %{
  techniques:
  - passes:
    - vert: vs
      frag: fs
      blendState:
        targets:
        - blend: true
      rasterizerState:
        cullMode: none
      properties:
        texture: { value: white }
        alphaThreshold: { value: 0.5 }
}%


CCProgram vs %{
  precision highp float;

  #include <cc-global>
  #include <cc-local>

  in vec3 a_position;
  in vec4 a_color;
  out vec4 v_color;

  #if USE_TEXTURE
  in vec2 a_uv0;
  out vec2 v_uv0;
  #endif

  void main () {
    vec4 pos = vec4(a_position, 1);

    #if CC_USE_MODEL
    pos = cc_matViewProj * cc_matWorld * pos;
    #else
    pos = cc_matViewProj * pos;
    #endif

    #if USE_TEXTURE
    v_uv0 = a_uv0;
    #endif

    v_color = a_color;

    gl_Position = pos;
  }
}%


CCProgram fs %{
  precision highp float;

  #include <alpha-test>
  #include <texture>
  #include <cc-global>

  in vec4 v_color;

  #if USE_TEXTURE
  in vec2 v_uv0;
  uniform sampler2D texture;
  #endif

	#define LAYERS 6
	#define DEPTH .4
	#define WIDTH .3
	#define SPEED .3
	#define DRIFT .2
	#define DRIFT_PROBABILITY 0.6
  #define iTime cc_time.x

  void main () {
    const mat3 p = mat3(13.323122,23.5112,21.71123,21.1212,28.7312,11.9312,21.8112,14.7212,61.3934);
	vec2 uv = 500./1000. + vec2(1.,1.)*gl_FragCoord.xy / 1000.;
	vec3 acc = vec3(0.0);
	float dof = 5.*sin(iTime*.1);
	for (int i=0;i<LAYERS;i++) {
		float fi = float(i);
		vec2 q = uv*(1.+fi*DEPTH);
		
		// 根据概率决定雪花是否斜向飘落
		float shouldDrift = step(DRIFT_PROBABILITY, fract(fi * 7.238917));
		float driftAmount = shouldDrift * DRIFT * sin(iTime * 0.5 + fi * 1.5) * (1.0 + 0.5 * sin(fi * 3.7));
		q += vec2(q.y*(WIDTH*mod(fi*7.238917,1.)-WIDTH*.5) + driftAmount, SPEED*iTime/(1.+fi*DEPTH*.03));
		
		vec3 n = vec3(floor(q),31.189+fi);
		vec3 m = floor(n)*.00001 + fract(n);
		vec3 mp = (31415.9+m)/fract(p*m);
		vec3 r = fract(mp);
		vec2 s = abs(mod(q,1.)-.5+.9*r.xy-.45);
		
		// 调整雪花大小范围，增加最小雪花尺寸
		s += .008*abs(2.*fract(8.*q.yx)-1.);
		float d = .5*max(s.x-s.y,s.x+s.y)+max(s.x,s.y)-.01;
		float edge = .004+.04*min(.5*abs(fi-5.-dof),1.);
		
		// 调整雪花大小变化范围，提高最小值
		float sizeVariation = 0.9 + 0.3 * sin(fi * 2.1);
		acc += vec3(smoothstep(edge,-edge,d)*(r.x/(1.+.02*fi*DEPTH)*sizeVariation));
	}
    float a = 0.;
    if(acc.r+acc.g+acc.b>0.3){
        a = acc.r+acc.g+acc.b;
    }
	gl_FragColor = vec4(vec3(acc*5.),a);

    // gl_FragColor = o;
  }
}%