Thus, for values of z up to dp (that is, points between the light source and the object 4), the primary depth
buffer 232 holds the classic z value, and the secondary depth buffer 233 holds the initialisation value, e.g. MAX_DEPTH.
In this form, it is evident that there is no need to compute the difference between the value stored in the first and second
buffers for points lying between the light source 2 and the closest object 4 because the secondary depth has not been
written. There is no shadow receiver. However, for values of z exceeding dp, that is points lying between the object 4
and the immediate second occlusion 10 (shadow receiver), the value which is held in the primary depth buffer remains
at dp while the value that is held in the secondary depth buffer is z, the classic depth. Consequently, the difference ∆
between the values held in the primary and secondary depth buffers provides the distance (if any) between the point
in the light the object 4 and the shadow that it casts on the shadow receiver 10. This distance characterises the intensity
of the shadow and its determination allows soft shadows to be rendered.
Thus, for values of z up to dp (that is, points between the light source and the object 4), the primary depth
buffer 232 holds the classic z value, and the secondary depth buffer 233 holds the initialisation value, e.g. MAX_DEPTH.
In this form, it is evident that there is no need to compute the difference between the value stored in the first and second
buffers for points lying between the light source 2 and the closest object 4 because the secondary depth has not been
written. There is no shadow receiver. However, for values of z exceeding dp, that is points lying between the object 4
and the immediate second occlusion 10 (shadow receiver), the value which is held in the primary depth buffer remains
at dp while the value that is held in the secondary depth buffer is z, the classic depth. Consequently, the difference ∆
between the values held in the primary and secondary depth buffers provides the distance (if any) between the point
in the light the object 4 and the shadow that it casts on the shadow receiver 10. This distance characterises the intensity
of the shadow and its determination allows soft shadows to be rendered.
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