path: Skip any secondary degenerate line-to segments.

Only the very first line-to following a move-to can have any
significance if degenerate whilst stroking, so skip all others.
In other words,

  0 0 m 0 0 l stroke

produces a capped degenerate path (i.e a dot),

  0 0 m 0 0 l 0 0 l stroke

produces the same degenerate stroke, and

  0 0 m 0 0 l 1 0 l stroke

produce a horizontal line.

1 files changed, 10 insertions, 3 deletions

diff --git a/src/cairo-path-fixed.c b/src/cairo-path-fixed.c
index db0e4937..42172c67 100644
--- a/src/cairo-path-fixed.c
+++ b/src/cairo-path-fixed.c
@@ -446,6 +446,16 @@ _cairo_path_fixed_line_to (cairo_path_fixed_t *path,
     if (! path->has_current_point)
 	return _cairo_path_fixed_move_to (path, point.x, point.y);
 
+    /* If the previous op was but the initial MOVE_TO and this segment
+     * is degenerate, then we can simply skip this point. Note that
+     * a move-to followed by a degenerate line-to is a valid path for
+     * stroking, but at all other times is simply a degenerate segment.
+     */
+    if (_cairo_path_last_op (path) != CAIRO_PATH_OP_MOVE_TO) {
+	if (x == path->current_point.x && y == path->current_point.y)
+	    return CAIRO_STATUS_SUCCESS;
+    }
+
     /* If the previous op was also a LINE_TO with the same gradient,
      * then just change its end-point rather than adding a new op.
      */
@@ -453,9 +463,6 @@ _cairo_path_fixed_line_to (cairo_path_fixed_t *path,
 	cairo_path_buf_t *buf;
 	const cairo_point_t *p;
 
-	if (x == path->current_point.x && y == path->current_point.y)
-	    return CAIRO_STATUS_SUCCESS;
-
 	buf = cairo_path_tail (path);
 	if (likely (buf->num_points >= 2)) {
 	    p = &buf->points[buf->num_points-2];