[cairo-commit] Branch '1.8' - src/cairo-matrix.c

[Chris Wilson]

 src/cairo-matrix.c |   26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

New commits:
commit 540de34453d16092acd2978b513831a02f01f59f
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Sun Oct 26 12:53:29 2008 +0000

    [matrix] Optimise invert for simple scaling|translation matrices.
    
    Peter Hercek reported, and provided a very useful test case for, a bug
    that caused his applications to crash with Cairo detecting an
    non-invertible pattern matrix and thus asserting the impossible happened.
    Bisecting revealed that the bug first appeared with 3c18d95 and
    disappeared with 0d0c6a1. Since neither of these explain the crash,
    further investigation revealed a compiler bug (gcc 4.3.3 20081130,
    earlier versions have different bugs!) that caused the matrix inversion
    to be invalid iff _cairo_matrix_scalar_multiply() was inlined (i.e. -O0,
    or an explicit noinline atttribute on that function prevented the bug, as
    did -msse.) So we apply this workaround to hide the bug in the stable
    series...
    
    The matrix is quite often just a simple scale and translate (or even
    identity!). For this class of matrix, we can skip the full adjoint
    rearrangement and determinant calculation and just compute the inverse
    directly.
    (cherry picked from commit 0d0c6a199c5b631299c72dce80d66ac0f4936a64)

diff --git a/src/cairo-matrix.c b/src/cairo-matrix.c
index ca18323..6a29aec 100644
--- a/src/cairo-matrix.c
+++ b/src/cairo-matrix.c
@@ -485,9 +485,33 @@ _cairo_matrix_compute_adjoint (cairo_matrix_t *matrix)
 cairo_status_t
 cairo_matrix_invert (cairo_matrix_t *matrix)
 {
-    /* inv (A) = 1/det (A) * adj (A) */
     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))