The difference ∆ is stored as part of the texture information in the frame buffer, such that the texture can then
be processed in order to define the degree of shadow for each pixel. During a rendering pass, a simple look-up operation
is utilised to render the penumbra, using the texture value as a mask. Moreover, by representing the distance ∆ as part
of the texture value, the results can be reused in subsequent passes at no cost. The mask constituted by the differences
∆ is referred to herein as the shadow mask and its generation is discussed in more detail below.