CocosCreator-Shader-Effect-Demo/assets/effects/glow-inner.effect

// Copyright (c) 2017-2018 Xiamen Yaji Software Co., Ltd.  
// 内发光特效
// 原理: 采样周边像素alpha取平均值，叠加发光效果
CCEffect %{
  techniques:
  - passes:
    - vert: vs
      frag: fs
      blendState:
        targets:
        - blend: true
      rasterizerState:
        cullMode: none
      properties:
        texture: { value: white }
        alphaThreshold: { value: 0.5 }
        glowColor: { value: [1.0, 1.0, 0.0, 1.0], editor: { type: color } }
        glowColorSize: { value: 0.01 }
}%


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>

  in vec4 v_color;

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

  #if SHOW_INNER_GLOW

  uniform glow {
    // 发光颜色
    vec4 glowColor;
    // 发光范围
    float glowColorSize;
    // 特别地，必须是 vec4 先于 float 声明
  };

  /**
   * 获取指定角度方向，距离为xxx的像素的透明度
   *
   * @param angle 角度 [0.0, 360.0]
   * @param distance 距离 [0.0, 1.0]
   *
   * @return alpha [0.0, 1.0]
   */
  float getColorAlpha(float angle, float distance) {
    // 角度转弧度，公式为：弧度 = 角度 * (pi / 180)
    float radian = angle * 0.01745329252; // 这个浮点数是 pi / 180
    vec4 color = texture(texture, v_uv0 + vec2(distance * cos(radian), distance * sin(radian))); 
    return 1.0 - color.a;
  }

  /**
   * 获取指定距离的周边像素的透明度平均值
   *
   * @param distance 距离 [0.0, 1.0]
   *
   * @return average alpha [0.0, 1.0]
   */
  float getDistanceAverageAlpha(float distance) {
    float totalAlpha = 0.0;
    totalAlpha += getColorAlpha(0.0, distance);
    totalAlpha += getColorAlpha(30.0, distance);
    totalAlpha += getColorAlpha(60.0, distance);
    totalAlpha += getColorAlpha(90.0, distance);
    totalAlpha += getColorAlpha(120.0, distance);
    totalAlpha += getColorAlpha(150.0, distance);
    totalAlpha += getColorAlpha(180.0, distance);
    totalAlpha += getColorAlpha(210.0, distance);
    totalAlpha += getColorAlpha(240.0, distance);
    totalAlpha += getColorAlpha(270.0, distance);
    totalAlpha += getColorAlpha(300.0, distance);
    totalAlpha += getColorAlpha(330.0, distance);
    return totalAlpha * (1.0 / 12.0);
  }

  /**
   * 获取发光的透明度
   */
  float getGlowAlpha() {
    float totalAlpha = 0.0;
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.1);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.2);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.3);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.4);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.5);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.6);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.7);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.8);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 0.9);
    totalAlpha += getDistanceAverageAlpha(glowColorSize * 1.0);
    return totalAlpha * (1.0 / 10.0);
  }

  #endif

  void main () {
    vec4 o = vec4(1, 1, 1, 1);

    #if USE_TEXTURE
    o *= texture(texture, v_uv0);
      #if CC_USE_ALPHA_ATLAS_TEXTURE
      o.a *= texture2D(texture, v_uv0 + vec2(0, 0.5)).r;
      #endif
    #endif

    o *= v_color;

    ALPHA_TEST(o);

    gl_FragColor = o;

    #if SHOW_INNER_GLOW
      // 先画图案
      vec4 color_dest = o;

      // 然后在图案上叠加内发光 
      vec4 color_src = glowColor * getGlowAlpha();

      // 按照这个顺序，源颜色就是内发光颜色，目标颜色就是图案颜色色 
      // 所以命名就是 color_src, color_dest

      // 按照混合颜色规则 http://docs.cocos.com/creator/manual/zh/advanced-topics/ui-auto-batch.html#blend-%E6%A8%A1%E5%BC%8F
      // 要在图案上方，叠加一个内发光，将两者颜色混合起来，那么最终选择的混合模式如下：
      // color_src: GL_SRC_ALPHA
      // color_dest: GL_ONE_MINUS_SRC_ALPHA
      // 即最终颜色如下：
      // color_src * GL_SRC_ALPHA + color_dest * GL_ONE_MINUS_SRC_ALPHA
      gl_FragColor = color_src * color_src.a + color_dest * (1.0 - color_src.a);
      // gl_FragColor = color_src  + color_dest * (1.0 - color_src.a);
      // gl_FragColor = color_src * (1.0 - color_src.a) + color_dest * color_src.a;
      // gl_FragColor = color_src;
      // gl_FragColor = color_dest * color_dest.a + color_src * (1.0 - color_dest.a);
    #endif
  }
}%