Allow src and dst to be identical in pixman_f_transform_invert()

It is useful to be able to invert a matrix in place, but currently
pixman_f_transform_invert() will produce wrong results if you pass the
same matrix as both source and destination.

Fix that by inverting into a temporary matrix and then copying that to
the destination.

diff --git a/pixman/pixman-matrix.c b/pixman/pixman-matrix.c
index a029ab7..d2ab609 100644 (file)
--- a/pixman/pixman-matrix.c
+++ b/pixman/pixman-matrix.c
@@ -336,14 +336,14 @@ PIXMAN_EXPORT pixman_bool_t
 pixman_transform_invert (struct pixman_transform *      dst,
                          const struct pixman_transform *src)
 {
-    struct pixman_f_transform m, r;
+    struct pixman_f_transform m;
 
     pixman_f_transform_from_pixman_transform (&m, src);
 
-    if (!pixman_f_transform_invert (&r, &m))
+    if (!pixman_f_transform_invert (&m, &m))
        return FALSE;
 
-    if (!pixman_transform_from_pixman_f_transform (dst, &r))
+    if (!pixman_transform_from_pixman_f_transform (dst, &m))
        return FALSE;
 
     return TRUE;
@@ -469,10 +469,11 @@ PIXMAN_EXPORT pixman_bool_t
 pixman_f_transform_invert (struct pixman_f_transform *      dst,
                            const struct pixman_f_transform *src)
 {
-    double det;
-    int i, j;
     static const int a[3] = { 2, 2, 1 };
     static const int b[3] = { 1, 0, 0 };
+    pixman_f_transform_t d;
+    double det;
+    int i, j;
 
     det = 0;
     for (i = 0; i < 3; i++)
@@ -507,10 +508,12 @@ pixman_f_transform_invert (struct pixman_f_transform *      dst,
            if (((i + j) & 1) != 0)
                p = -p;
            
-           dst->m[j][i] = det * p;
+           d.m[j][i] = det * p;
        }
     }
 
+    *dst = d;
+
     return TRUE;
 }