NAME

       al_check_inverse - Allegro 5 API

SYNOPSIS

              #include <allegro5/allegro.h>

              int al_check_inverse(const ALLEGRO_TRANSFORM *trans, float tol)

DESCRIPTION

       Checks  if  the  transformation has an inverse using the supplied tolerance.  Tolerance should be a small
       value between 0 and 1, with 1e-7 being sufficient for most applications.

       In this function tolerance specifies how close the determinant can be to 0 (if the determinant is 0,  the
       transformation  has no inverse).  Thus the smaller the tolerance you specify, the "worse" transformations
       will pass this test.  Using a tolerance of 1e-7 will catch errors greater than 1/1000's of a  pixel,  but
       let  smaller  errors  pass.   That  means  that  if  you transformed a point by a transformation and then
       transformed it again by the inverse transformation that passed this check,  the  resultant  point  should
       less than 1/1000's of a pixel away from the original point.

       Note  that  this  check  is  superfluous  most of the time if you never touched the transformation matrix
       values yourself.  The only thing that would cause the transformation to not have an  inverse  is  if  you
       applied  a 0 (or very small) scale to the transformation or you have a really large translation.  As long
       as the scale is comfortably above 0, the transformation will be invertible.

       Parameters:

       • trans - Transformation to check

       • tol - Tolerance

       Returns: 1 if the transformation is invertible, 0 otherwise

SEE ALSO

       al_invert_transform(3alleg5)

Allegro reference manual                                                             al_check_inverse(3alleg5)()