cocos drawNode分析

void GLProgramCache::loadDefaultGLPrograms()
{
    GLProgram *p = new (std::nothrow) GLProgram();
    // 加载对应的shader，kShaderType_PositionTextureColor来自#include "*.(frag,vert)"的字符串变量
    // 参考 https://www.zhihu.com/question/431645051
    loadDefaultGLProgram(p, kShaderType_PositionTextureColor);
    // 更新目标字符串
    _programs.emplace(GLProgram::SHADER_NAME_POSITION_TEXTURE_COLOR, p);
}

drawNode使用的是GLProgram::SHADER_NAME_POSITION_LENGTH_TEXTURE_COLOR

const char* ccPositionColorLengthTexture_vert = R"(

#ifdef GL_ES
precision lowp float;
#endif

#ifdef GL_ES
attribute mediump vec4 a_position;
attribute mediump vec2 a_texcoord;
attribute mediump vec4 a_color;

varying mediump vec4 v_color;
varying mediump vec2 v_texcoord;

#else

attribute vec4 a_position;
attribute vec2 a_texcoord;
attribute vec4 a_color;

varying vec4 v_color;
varying vec2 v_texcoord;

#endif

uniform float u_alpha;

void main()
{
    v_color = vec4(a_color.rgb * a_color.a * u_alpha, a_color.a * u_alpha);
    v_texcoord = a_texcoord;

    gl_Position = CC_MVPMatrix * a_position;
}
)";

const char* ccPositionColorLengthTexture_frag = R"(

#ifdef GL_ES
// #extension GL_OES_standard_derivatives : enable

varying mediump vec4 v_color;
varying mediump vec2 v_texcoord;
#else
varying vec4 v_color;
varying vec2 v_texcoord;
#endif

void main()
{
// #if defined GL_OES_standard_derivatives
// gl_FragColor = v_color*smoothstep(0.0, length(fwidth(v_texcoord)), 1.0 - length(v_texcoord));
// #else
    gl_FragColor = v_color*step(0.0, 1.0 - length(v_texcoord));
// #endif
}
)";

MontionStreak使用的GLProgram::SHADER_NAME_POSITION_TEXTURE_COLOR

const char* ccPositionTextureColor_vert = R"(
attribute vec4 a_position;
attribute vec2 a_texCoord;
attribute vec4 a_color;

#ifdef GL_ES
varying lowp vec4 v_fragmentColor;
varying mediump vec2 v_texCoord;
#else
varying vec4 v_fragmentColor;
varying vec2 v_texCoord;
#endif

void main()
{
    gl_Position = CC_MVPMatrix * a_position;
    v_fragmentColor = a_color;
    v_texCoord = a_texCoord;
}
)";

const char* ccPositionTextureColor_frag = R"(
#ifdef GL_ES
precision lowp float;
#endif

varying vec4 v_fragmentColor;
varying vec2 v_texCoord;

void main()
{
    gl_FragColor = v_fragmentColor * texture2D(CC_Texture0, v_texCoord);
}
)";