test: Ignore single-bit errors for SVG backend.

The interface of the various buffer/image_diff functions is improved to
provide the maximum pixel difference in addition to the number of pixels
that differ. This value can then be used to compare against a per-backend
tolerance.

Currently I've set the SVG backend's tolerance to 1 to handle some issues
we're currently seeing of single-bit differences on different systems, (but
we're not exactly sure why yet).

Also I improved the image_diff routines to properly report a status value
on failure rather than the bogus value of -1 for pixels_changed.

1 files changed, 47 insertions, 16 deletions

diff --git a/test/buffer-diff.h b/test/buffer-diff.h
index 2be2b3955..bef42cffe 100644
--- a/test/buffer-diff.h
+++ b/test/buffer-diff.h
@@ -1,36 +1,50 @@
 /* imagediff - Compare two images
  *
  * Copyright © 2004 Richard D. Worth
+ * Copyright © 2006 Red Hat, Inc.
  *
  * Permission to use, copy, modify, distribute, and sell this software
  * and its documentation for any purpose is hereby granted without
  * fee, provided that the above copyright notice appear in all copies
  * and that both that copyright notice and this permission notice
- * appear in supporting documentation, and that the name of Richard Worth
+ * appear in supporting documentation, and that the name of the authors
  * not be used in advertising or publicity pertaining to distribution
  * of the software without specific, written prior permission.
- * Richard Worth makes no representations about the suitability of this
+ * The authors make no representations about the suitability of this
  * software for any purpose.  It is provided "as is" without express
  * or implied warranty.
  *
- * RICHARD WORTH DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * THE AUTHORS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
  * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
- * NO EVENT SHALL RICHARD WORTH BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
  * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
  * OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
  * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  *
- * Author: Richard D. Worth <richard@theworths.org> */
+ * Authors: Richard D. Worth <richard@theworths.org>
+ *	    Carl Worth <cworth@cworth.org>
+ */
 
 #ifndef BUFFER_DIFF_H
 #define BUFFER_DIFF_H
 
-/* Returns number of pixels changed.
+#include "cairo-test.h"
+
+typedef struct _buffer_diff_result {
+    unsigned int pixels_changed;
+    unsigned int max_diff;
+} buffer_diff_result_t;
+
+/* Compares two image buffers.
+ *
+ * Provides number of pixels changed and maximum single-channel
+ * difference in result.
+ *
  * Also fills in a "diff" buffer intended to visually show where the
  * images differ.
  */
-int
+void
 buffer_diff (unsigned char *buf_a,
 	     unsigned char *buf_b,
 	     unsigned char *buf_diff,
@@ -38,13 +52,18 @@ buffer_diff (unsigned char *buf_a,
 	     int	    height,
 	     int	    stride_a,
 	     int	    stride_b,
-	     int	    stride_diff);
+	     int	    stride_diff,
+	     buffer_diff_result_t *result);
 
-/* Returns number of pixels changed ignoring the alpha channel.
+/* Compares two image buffers ignoring the alpha channel.
+ *
+ * Provides number of pixels changed and maximum single-channel
+ * difference in result.
+ *
  * Also fills in a "diff" buffer intended to visually show where the
  * images differ.
  */
-int
+void
 buffer_diff_noalpha (unsigned char *buf_a,
 		     unsigned char *buf_b,
 		     unsigned char *buf_diff,
@@ -52,29 +71,41 @@ buffer_diff_noalpha (unsigned char *buf_a,
 		     int	    height,
 		     int	    stride_a,
 		     int	    stride_b,
-		     int	    stride_diff);
+		     int	    stride_diff,
+		     buffer_diff_result_t *result);
 
-/* Returns number of pixels changed, (or -1 on error).
+/* Compares two image buffers ignoring the alpha channel. A return
+ * value of CAIRO_STATUS_SUCCESS indicates that a comparison was made,
+ * (but the images may or may not differ). Failure modes include
+ * CAIRO_STATUS_FILE_NOT_FOUND, CAIRO_STATUS_READ_ERROR,
+ * CAIRO_STATUS_NO_MEMORY, and CAIRO_STATUS_SURFACE_TYPE_MISMATCH
+ * (which is used if the image sizes differ).
+ *
+ * Provides number of pixels changed and maximum single-channel
+ * difference in result.
+ *
  * Also saves a "diff" image intended to visually show where the
  * images differ.
  */
-int
+cairo_status_t
 image_diff (const char *filename_a,
 	    const char *filename_b,
 	    const char *filename_diff,
 	    int		ax,
 	    int		ay,
 	    int		bx,
-	    int		by);
+	    int		by,
+	    buffer_diff_result_t *result);
 
 /* Like image_diff, but blending the contents of b over white first. */
-int
+cairo_status_t
 image_diff_flattened (const char *filename_a,
 		      const char *filename_b,
 		      const char *filename_diff,
                       int         ax,
                       int         ay,
                       int         bx,
-                      int         by);
+                      int         by,
+		      buffer_diff_result_t *result);
 
 #endif