In this example, we mixed the two texture colors together using the alpha value of the second texture. This is just one of many options for mixing the texture colors. There are a number of different choices here, and your choice will be dependent on the kind of texture data available and the desired effect. A popular technique is to use an additional vertex attribute to augment the amount of blending between the textures. This additional vertex attribute would allow us to vary the blending factor throughout a model. For example, we could vary the amount of moss that grows on a surface by defining another vertex attribute that would control the amount of blending between the moss texture and the base texture. A value of zero might correspond to zero moss, up to a value of one, which would enable blending based on the texture's alpha value alone.