1 files changed, 41 insertions, 24 deletions

diff --git a/src/cairo-matrix.c b/src/cairo-matrix.c
index b644dec8..6dfe537f 100644
--- a/src/cairo-matrix.c
+++ b/src/cairo-matrix.c
@@ -865,7 +865,9 @@ _cairo_matrix_transformed_circle_major_axis (cairo_matrix_t *matrix, double radi
 
 void
 _cairo_matrix_to_pixman_matrix (const cairo_matrix_t	*matrix,
-				pixman_transform_t	*pixman_transform)
+				pixman_transform_t	*pixman_transform,
+				double xc,
+				double yc)
 {
     static const pixman_transform_t pixman_identity_transform = {{
         {1 << 16,        0,       0},
@@ -875,11 +877,9 @@ _cairo_matrix_to_pixman_matrix (const cairo_matrix_t	*matrix,
 
     if (_cairo_matrix_is_identity (matrix)) {
         *pixman_transform = pixman_identity_transform;
-    }
-    else {
+    } else {
         cairo_matrix_t inv;
-        double x,y;
-        pixman_vector_t vector;
+	unsigned max_iterations;
 
         pixman_transform->matrix[0][0] = _cairo_fixed_16_16_from_double (matrix->xx);
         pixman_transform->matrix[0][1] = _cairo_fixed_16_16_from_double (matrix->xy);
@@ -899,9 +899,10 @@ _cairo_matrix_to_pixman_matrix (const cairo_matrix_t	*matrix,
          * for cairo, while pixman uses rounded versions of xx ... yy.
          * This error increases as a and b get larger.
          *
-         * To compensate for this, we fix the point (0, 0) in pattern
+         * To compensate for this, we fix the point (xc, yc) in pattern
          * space and adjust pixman's transform to agree with cairo's at
-         * that point. */
+         * that point.
+	 */
 
 	if (_cairo_matrix_is_translation (matrix))
 	    return;
@@ -911,22 +912,38 @@ _cairo_matrix_to_pixman_matrix (const cairo_matrix_t	*matrix,
         if (cairo_matrix_invert (&inv) != CAIRO_STATUS_SUCCESS)
             return;
 
-        /* find the device space coordinate that maps to (0, 0) */
-        x = 0, y = 0;
-        cairo_matrix_transform_point (&inv, &x, &y);
-
-        /* transform the resulting device space coordinate back
-         * to the pattern space, using pixman's transform */
-        vector.vector[0] = _cairo_fixed_16_16_from_double (x);
-        vector.vector[1] = _cairo_fixed_16_16_from_double (y);
-        vector.vector[2] = 1 << 16;
-
-        if (! pixman_transform_point_3d (pixman_transform, &vector))
-            return;
-
-        /* Ideally, the vector should now be (0, 0). We can now compensate
-         * for the resulting error */
-        pixman_transform->matrix[0][2] -= vector.vector[0];
-        pixman_transform->matrix[1][2] -= vector.vector[1];
+        /* find the pattern space coordinate that maps to (xc, yc) */
+	xc += .5; yc += .5; /* offset for the pixel centre */
+	max_iterations = 5;
+	do {
+	    double x,y;
+	    pixman_vector_t vector;
+	    cairo_fixed_16_16_t dx, dy;
+
+	    vector.vector[0] = _cairo_fixed_16_16_from_double (xc);
+	    vector.vector[1] = _cairo_fixed_16_16_from_double (yc);
+	    vector.vector[2] = 1 << 16;
+
+	    if (! pixman_transform_point_3d (pixman_transform, &vector))
+		return;
+
+	    x = pixman_fixed_to_double (vector.vector[0]);
+	    y = pixman_fixed_to_double (vector.vector[1]);
+	    cairo_matrix_transform_point (&inv, &x, &y);
+
+	    /* Ideally, the vector should now be (xc, yc).
+	     * We can now compensate for the resulting error.
+	     */
+	    x -= xc;
+	    y -= yc;
+	    cairo_matrix_transform_distance (matrix, &x, &y);
+	    dx = _cairo_fixed_16_16_from_double (x);
+	    dy = _cairo_fixed_16_16_from_double (y);
+	    pixman_transform->matrix[0][2] -= dx;
+	    pixman_transform->matrix[1][2] -= dy;
+
+	    if (dx == 0 && dy == 0)
+		break;
+	} while (--max_iterations);
     }
 }