/**
* cairo_matrix_invert:
* @matrix: a @cairo_matrix_t
*
* Changes @matrix to be the inverse of it's original value. Not
* all transformation matrices have inverses; if the matrix
* collapses points together (it is <firstterm>degenerate</firstterm>),
* then it has no inverse and this function will fail.
*
* Returns: If @matrix has an inverse, modifies @matrix to
* be the inverse matrix and returns %CAIRO_STATUS_SUCCESS. Otherwise,
* returns %CAIRO_STATUS_INVALID_MATRIX.
**/
cairo_status_t
cairo_matrix_invert (cairo_matrix_t *matrix)
{
/* inv (A) = 1/det (A) * adj (A) */
double det;
_cairo_matrix_compute_determinant (matrix, &det);
if (det == 0)
return CAIRO_STATUS_INVALID_MATRIX;
_cairo_matrix_compute_adjoint (matrix);
_cairo_matrix_scalar_multiply (matrix, 1 / det);
return CAIRO_STATUS_SUCCESS;
}
/**
* cairo_matrix_invert:
* @matrix: a #cairo_matrix_t
*
* Changes @matrix to be the inverse of its original value. Not
* all transformation matrices have inverses; if the matrix
* collapses points together (it is <firstterm>degenerate</firstterm>),
* then it has no inverse and this function will fail.
*
* Returns: If @matrix has an inverse, modifies @matrix to
* be the inverse matrix and returns %CAIRO_STATUS_SUCCESS. Otherwise,
* returns %CAIRO_STATUS_INVALID_MATRIX.
**/
cairo_status_t
cairo_matrix_invert (cairo_matrix_t *matrix)
{
double det;
/* Simple scaling|translation matrices are quite common... */
if (matrix->xy == 0. && matrix->yx == 0.) {
matrix->x0 = -matrix->x0;
matrix->y0 = -matrix->y0;
if (matrix->xx != 1.) {
if (matrix->xx == 0.)
return _cairo_error (CAIRO_STATUS_INVALID_MATRIX);
matrix->xx = 1. / matrix->xx;
matrix->x0 *= matrix->xx;
}
if (matrix->yy != 1.) {
if (matrix->yy == 0.)
return _cairo_error (CAIRO_STATUS_INVALID_MATRIX);
matrix->yy = 1. / matrix->yy;
matrix->y0 *= matrix->yy;
}
return CAIRO_STATUS_SUCCESS;
}
/* inv (A) = 1/det (A) * adj (A) */
det = _cairo_matrix_compute_determinant (matrix);
if (! ISFINITE (det))
return _cairo_error (CAIRO_STATUS_INVALID_MATRIX);
if (det == 0)
return _cairo_error (CAIRO_STATUS_INVALID_MATRIX);
_cairo_matrix_compute_adjoint (matrix);
_cairo_matrix_scalar_multiply (matrix, 1 / det);
return CAIRO_STATUS_SUCCESS;
}
