al_check_inverse(3)al_check_inverse(3)NAMEal_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 toler‐
ance. 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 ALSOal_invert_transform(3)Allegro reference manualal_check_inverse(3)
