Implements a mask component for a layered texture.
A texture mask is used in a non-destructive process to hide some portions of a texture layer and reveal others. White values in the mask allow the full value of the underlying texture layer to be shown, and black values in the mask completely block the underlying texture layer from being shown. The range of values between white and black gradually transition between completely shown and completely blocked. When color values are used in the mask, the value of each RGB channel in the color has the same effect on whether or not that channel is shown or blocked.