CCEffect %{
  techniques:
  - passes:
    - vert: rainbow-water-vs
      frag: rainbow-water-fs
      blendState:
        targets:
        - blend: true
          blendSrc: src_alpha
          blendDst: one_minus_src_alpha
      rasterizerState:
        cullMode: none
      depthStencilState:
        depthTest: false
        depthWrite: false
      properties:
        texture: { value: white }
        uvRect: { value: [0, 0, 1, 1] }
        uvRotated: { value: 0 }
        water: { value: [1, 0, 0.024, 0.006] }
}%

CCProgram rainbow-water-vs %{
  precision highp float;
  #include <cc-global>
  #include <cc-local>
  in vec3 a_position;
  in vec4 a_color;
  in vec2 a_uv0;
  out vec4 v_color;
  out vec2 v_uv0;

  void main () {
    vec4 pos = vec4(a_position, 1.0);
    #if CC_USE_MODEL
      pos = cc_matViewProj * cc_matWorld * pos;
    #else
      pos = cc_matViewProj * pos;
    #endif
    gl_Position = pos;
    v_color = a_color;
    v_uv0 = a_uv0;
  }
}%

CCProgram rainbow-water-fs %{
  #if CC_SUPPORT_standard_derivatives
    #extension GL_OES_standard_derivatives : enable
  #endif
  precision highp float;
  #include <texture>
  in vec4 v_color;
  in vec2 v_uv0;
  uniform sampler2D texture;
  uniform WaterProperties {
    vec4 uvRect;
    vec4 water;
    float uvRotated;
  };

  void main () {
    vec2 uv = (v_uv0 - uvRect.xy) / max(uvRect.zw, vec2(0.00001));
    if (uvRotated > 0.5) uv = vec2(uv.y, 1.0 - uv.x);
    vec4 base = vec4(1.0);
    {
      CCTexture(texture, v_uv0, base);
    }

    // 固定波形从左向右平移，瓶内颜色跟随同一波列，不在中途叠出新的凸起。
    float phase = uv.x * 7.5 - water.y * 1.8;
    float envelope = 4.0 * uv.y * (1.0 - uv.y);
    vec2 drift = vec2(0.0, 0.75 * sin(phase + uv.y * 3.0));
    vec2 flowingUV = clamp(uv + drift * water.z * envelope, vec2(0.001), vec2(0.999));
    if (uvRotated > 0.5) flowingUV = vec2(1.0 - flowingUV.y, flowingUV.x);
    vec4 flowing = vec4(1.0);
    {
      CCTexture(texture, uvRect.xy + flowingUV * uvRect.zw, flowing);
    }
    vec4 color = vec4(mix(base.rgb, flowing.rgb, flowing.a), base.a);

    // 液面沿同一方向连续推进；空瓶不残留，满瓶保持完整。
    float amplitude = water.z * smoothstep(0.0, 0.08, water.x)
        * smoothstep(0.0, 0.08, 1.0 - water.x);
    float wave = amplitude * sin(phase);
    float surface = water.x + wave;
    float height = 1.0 - uv.y;
    float distanceToSurface = height - surface;
    float feather = water.w;
    #if CC_SUPPORT_standard_derivatives
      // 按实际屏幕像素抗锯齿，缩小瓶子后液面仍能平滑跨过像素边界。
      feather = max(0.75 * fwidth(distanceToSurface), 0.00001);
    #endif
    if (water.x <= 0.0) {
      color.a = 0.0;
    } else if (water.x < 1.0) {
      color.a *= 1.0 - smoothstep(-feather, feather, distanceToSurface);
      float rim = 1.0 - smoothstep(0.0, feather, abs(distanceToSurface));
      color.rgb = mix(color.rgb, vec3(1.0, 0.98, 0.88), rim * 0.08);
    }
    color *= v_color;
    #if USE_BGRA
      gl_FragColor = color.bgra;
    #else
      gl_FragColor = color;
    #endif
  }
}%