diff options
Diffstat (limited to 'src/cairo-matrix.c')
| -rw-r--r-- | src/cairo-matrix.c | 37 |
1 files changed, 23 insertions, 14 deletions
diff --git a/src/cairo-matrix.c b/src/cairo-matrix.c index ba975beae..ae498f515 100644 --- a/src/cairo-matrix.c +++ b/src/cairo-matrix.c @@ -748,23 +748,32 @@ _cairo_matrix_is_integer_translation (const cairo_matrix_t *matrix, return FALSE; } +#define SCALING_EPSILON _cairo_fixed_to_double(1) + +/* This only returns true if the matrix is 90 degree rotations or + * flips. It appears calling code is relying on this. It will return + * false for other rotations even if the scale is one. Approximations + * are allowed to handle matricies filled in using trig functions + * such as sin(M_PI_2). + */ cairo_bool_t _cairo_matrix_has_unity_scale (const cairo_matrix_t *matrix) { - if (matrix->xy == 0.0 && matrix->yx == 0.0) { - if (! (matrix->xx == 1.0 || matrix->xx == -1.0)) - return FALSE; - if (! (matrix->yy == 1.0 || matrix->yy == -1.0)) - return FALSE; - } else if (matrix->xx == 0.0 && matrix->yy == 0.0) { - if (! (matrix->xy == 1.0 || matrix->xy == -1.0)) - return FALSE; - if (! (matrix->yx == 1.0 || matrix->yx == -1.0)) - return FALSE; - } else - return FALSE; - - return TRUE; + /* check that the determinant is near +/-1 */ + double det = _cairo_matrix_compute_determinant (matrix); + if (fabs (det * det - 1.0) < SCALING_EPSILON) { + /* check that one axis is close to zero */ + if (fabs (matrix->xy) < SCALING_EPSILON && + fabs (matrix->yx) < SCALING_EPSILON) + return TRUE; + if (fabs (matrix->xx) < SCALING_EPSILON && + fabs (matrix->yy) < SCALING_EPSILON) + return TRUE; + /* If rotations are allowed then it must instead test for + * orthogonality. This is xx*xy+yx*yy ~= 0. + */ + } + return FALSE; } /* By pixel exact here, we mean a matrix that is composed only of |