cocos creator2.4.8 合批的shader

测试例子：1122，红色绿色，字号20、 50

cc.dynamicAtlasManager.showDebug(true);

动态图集情况如下：
label.CacheModel="bitmap"，

label.CacheModel="char"

可以观察到无论哪种模式，只要label使用的字号，颜色，字体不同，都会进行单独的渲染，注意这里的颜色，也会受影响，原因是shader里面不处理node color导致的。

即如果label除了颜色剩下的属性都相同，都会生成同等颜色个数的label。

通过spector.js可以找到对应的shader

Creator\2.4.8\resources\static\default-assets\resources\effects\builtin-2d-sprite.effect

// 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>

  in vec4 v_color;

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

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

    #if USE_TEXTURE
      CCTexture(texture, v_uv0, o);
    #endif

    o *= v_color;

    ALPHA_TEST(o);

    #if USE_BGRA
      gl_FragColor = o.bgra;
    #else
      gl_FragColor = o.rgba;
    #endif
  }
}%

展开后的shader：

#define USE_TEXTURE 1
#define CC_USE_MODEL 0
#define USE_ALPHA_TEST 0
#define CC_USE_ALPHA_ATLAS_texture 0
#define INPUT_IS_GAMMA 0
#define USE_BGRA 0

precision highp float;
uniform mat4 cc_matViewProj;
uniform mat4 cc_matWorld;
attribute vec3 a_position;
attribute vec4 a_color;
varying vec4 v_color;
#if USE_TEXTURE
    attribute vec2 a_uv0;
    varying 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;
}

#define USE_TEXTURE 1
#define CC_USE_MODEL 0
#define USE_ALPHA_TEST 0
#define CC_USE_ALPHA_ATLAS_texture 0
#define INPUT_IS_GAMMA 0
#define USE_BGRA 0

precision highp float;
#if USE_ALPHA_TEST
    uniform float alphaThreshold;
#endif
void ALPHA_TEST (in vec4 color) {
    #if USE_ALPHA_TEST
        if (color.a < alphaThreshold) discard;
    #endif
}
void ALPHA_TEST (in float alpha) {
    #if USE_ALPHA_TEST
        if (alpha < alphaThreshold) discard;
    #endif
}
varying vec4 v_color;
#if USE_TEXTURE
    varying vec2 v_uv0;
    uniform sampler2D texture;
#endif
void main () {
    vec4 o = vec4(1, 1, 1, 1);
    #if USE_TEXTURE
        vec4 texture_tmp = texture2D(texture, v_uv0);
        #if CC_USE_ALPHA_ATLAS_texture
            texture_tmp.a *= texture2D(texture, v_uv0 + vec2(0, 0.5)).r;
        #endif
        #if INPUT_IS_GAMMA
            o.rgb *= (texture_tmp.rgb * texture_tmp.rgb);
            o.a *= texture_tmp.a;
        #else
            o *= texture_tmp;
        #endif
    #endif
    o *= v_color;
    ALPHA_TEST(o);
    #if USE_BGRA
        gl_FragColor = o.bgra;
    #else
        gl_FragColor = o.rgba;
    #endif
}

可以看到

o*=v_color;

如果字符纹理都是白色的，顶点颜色v_color如果传递过来相乘，是能够得到正确的颜色的

那为啥creator不这么做呢？

Creator\2.4.8\resources\engine\cocos2d\core\renderer\webgl\assemblers\label\2d\letter.js

 _getColor (comp) {
        WHITE._fastSetA(comp.node._color.a);
        return WHITE._val;
    }

    updateColor (comp) {
        let color = this._getColor(comp);

        super.updateColor(comp, color);
    }

可以看到在组装数据的时候，会舍弃掉node.color的颜色，只保留透明度，看来还是有优化空间的

混合有bug导致这么做