Cocos2d-lua 初識shader之五：定時器

在GLProgram::setUniformsForBuiltins函數中有下面代碼：

 
if(_flags.usesTime) {
    // This doesn't give the most accurate global time value.
    // Cocos2D doesn't store a high precision time value, so this will have to do.
    // Getting Mach time per frame per shader using time could be extremely expensive.
    float time = _director->getTotalFrames() * _director->getAnimationInterval();
        
    setUniformLocationWith4f(_builtInUniforms[GLProgram::UNIFORM_TIME], time/10.0, time, time*2, time*4);
    setUniformLocationWith4f(_builtInUniforms[GLProgram::UNIFORM_SIN_TIME], time/8.0, time/4.0, time/2.0, sinf(time));
    setUniformLocationWith4f(_builtInUniforms[GLProgram::UNIFORM_COS_TIME], time/8.0, time/4.0, time/2.0, cosf(time));
}

即Cocos在刷新時，已經將時間傳入進來了，可以在shader 中調用CC_Time，CC_SinTime和CC_CosTime這三個量來進行操作

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