scene_gap - Number controlling the scene z-sorting algorithm behaviour. Allegro game programming library.

       This  number  (default  value = 100.0) controls the behaviour of the z-sorting algorithm. When an edge is
       very close to another's polygon plane, there is an interval of uncertainty in which you cannot tell which
       object is visible (which z is smaller). This is due to cumulative numerical errors for  edges  that  have
       undergone a lot of transformations and interpolations.

       The  default  value means that if the 1/z values (in projected space) differ by only 1/100 (one percent),
       they are considered to be equal and the x-slopes of the planes are  used  to  find  out  which  plane  is
       getting closer when we move to the right.

       Larger  values  means  narrower margins, and increasing the chance of missing true adjacent edges/planes.
       Smaller values means larger margins, and increasing the chance of mistaking close polygons  for  adjacent
       ones.   The  value  of 100 is close to the optimum. However, the optimum shifts slightly with resolution,
       and may be application-dependent. It is here for you to fine-tune.

       scene_gap - Number controlling the scene z-sorting algorithm behaviour. Allegro game programming library.

create_scene(3alleg4),     clear_scene(3alleg4),      destroy_scene(3alleg4),      render_scene(3alleg4),
       scene_polygon3d(3alleg4)

Allegro                                           version 4.4.3                               scene_gap(3alleg4)

#include<allegro.h>externfloatscene_gap;