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The shaders have access to some _uniforms _ (see shaders for more info on shaders and uniforms) that are set by the game: the area flags, the world time, ... and the one we will use in this tutorial areaGlobalWind which contains the global wind vector for the area.
¿Why this uniform? because this uniform can be changed in a per player basis, so we can change the value of _areaGlobalWind _ for only one player. There are sureley other uniforms that can be used but, as we will see, this one allows an easy way for the shader to detect we want to apply a specific effect without affecting, at least noticeably, the wind effects in the area.
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