For describing the shadow mask as a texture, the shadow mask itself takes the form of a floating-point memory
surface 234, initialised to (1.0, 1.0, 1.0, 1.0). For each of its cells, the delta ∆ previously generated determines the
corresponding level of blur. The ∆ value permits the index of the texture to be determined from the texture hierarchy,
the index being used to simulate the level of blur at this pixel location. In the following equation, Tex_pixel is an index
in the hierarchy of textures extending between TEXMIN and TEXMAX (see Figure 4).