reftests: Allow minor differences to be toleratedwip/smcv/reftest-tolerance

Based on an earlier patch by Michael Biebl, as used in Debian's GTK 3
packaging, with additional inspiration from librsvg's reftests.

Each .ui or .node reftest can have an accompanying .keyfile file
like this:

    [reftest]
    accepted-diff-level=2
    accepted-diff-pixels=100
    tolerated-diff-level=20
    tolerated-diff-pixels=1000

If the number of pixels that differ from the reference is no more than
accepted-diff-pixels, and each channel in each of those pixels differs
from the reference by no more than accepted-diff-level, then we consider
that to be a full success, and don't even save the .diff.png for
analysis.

If that check fails, but the number of pixels that differ is no more
than tolerated-diff-pixels and the differences are no more than
tolerated-diff-level, then we treat it as a success with warnings, save
the .diff.png for analysis, and use g_test_incomplete() to record the
test-case as "TODO".

Signed-off-by: Simon McVittie <smcv@debian.org>

3 files changed, 83 insertions, 5 deletions

diff --git a/testsuite/gsk/compare-render.c b/testsuite/gsk/compare-render.c
index da6f9e2eb2..a4afd757ae 100644
--- a/testsuite/gsk/compare-render.c
+++ b/testsuite/gsk/compare-render.c
@@ -98,6 +98,12 @@ get_output_file (const char *file,
   return result;
 }
 
+static char *
+get_test_keyfile (const char *node_file)
+{
+  return file_replace_extension (node_file, ".node", ".keyfile");
+}
+
 static void
 save_image (cairo_surface_t *surface,
             const char      *test_name,
@@ -242,12 +248,45 @@ main (int argc, char **argv)
 
       if (diff_surface)
         {
+          char *keyfile_path = get_test_keyfile (node_file);
+          GKeyFile *keyfile = g_key_file_new ();
+          guint64 tolerated_diff = 0;
+          guint64 tolerated_pixels = 0;
+          guint64 accepted_diff = 0;
+          guint64 accepted_pixels = 0;
+
+          if (keyfile_path != NULL && g_file_test (keyfile_path, G_FILE_TEST_EXISTS))
+            {
+              GError *error = NULL;
+              g_key_file_load_from_file (keyfile, keyfile_path, G_KEY_FILE_NONE, &error);
+              g_assert_no_error (error);
+              accepted_diff = g_key_file_get_uint64 (keyfile, "reftest", "accepted-diff-level", NULL);
+              g_print ("Maximum difference accepted: %" G_GUINT64_FORMAT " levels\n", accepted_diff);
+              accepted_pixels = g_key_file_get_uint64 (keyfile, "reftest", "accepted-diff-pixels", NULL);
+              g_print ("Different pixels accepted: %" G_GUINT64_FORMAT "\n", accepted_pixels);
+              tolerated_diff = g_key_file_get_uint64 (keyfile, "reftest", "tolerated-diff-level", NULL);
+              g_print ("Maximum difference tolerated: %" G_GUINT64_FORMAT " levels\n", tolerated_diff);
+              tolerated_pixels = g_key_file_get_uint64 (keyfile, "reftest", "tolerated-diff-pixels", NULL);
+              g_print ("Different pixels tolerated: %" G_GUINT64_FORMAT "\n", tolerated_pixels);
+            }
+
           g_print ("%u (out of %u) pixels differ from reference by up to %u levels\n",
                    pixels_changed, pixels, max_diff);
 
-          save_image (diff_surface, node_file, ".diff.png");
+          if (max_diff > accepted_diff || pixels_changed > accepted_pixels)
+            save_image (diff_surface, node_file, ".diff.png");
+
           cairo_surface_destroy (diff_surface);
-          success = FALSE;
+
+          if (max_diff <= accepted_diff && pixels_changed <= accepted_pixels)
+            g_print ("differences are within acceptable range\n");
+          else if (max_diff <= tolerated_diff && pixels_changed <= tolerated_pixels)
+            g_print ("not right, but close enough\n");
+          else
+            g_test_fail ();
+
+          g_key_file_unref (keyfile);
+          g_free (keyfile_path);
         }
     }
 
diff --git a/testsuite/reftests/gtk-reftest.c b/testsuite/reftests/gtk-reftest.c
index 6ef17aa12a..791e95c849 100644
--- a/testsuite/reftests/gtk-reftest.c
+++ b/testsuite/reftests/gtk-reftest.c
@@ -290,6 +290,12 @@ save_image (cairo_surface_t *surface,
   g_free (filename);
 }
 
+static char *
+get_test_keyfile (const char *ui_file)
+{
+  return get_test_file (ui_file, ".keyfile", TRUE);
+}
+
 static void
 test_ui_file (GFile *file)
 {
@@ -326,10 +332,43 @@ test_ui_file (GFile *file)
 
   if (diff_image)
     {
+      char *keyfile_path = get_test_keyfile (ui_file);
+      GKeyFile *keyfile = g_key_file_new ();
+      guint64 tolerated_diff = 0;
+      guint64 tolerated_pixels = 0;
+      guint64 accepted_diff = 0;
+      guint64 accepted_pixels = 0;
+
+      if (keyfile_path != NULL)
+        {
+          GError *error = NULL;
+          g_key_file_load_from_file (keyfile, keyfile_path, G_KEY_FILE_NONE, &error);
+          g_assert_no_error (error);
+          accepted_diff = g_key_file_get_uint64 (keyfile, "reftest", "accepted-diff-level", NULL);
+          g_test_message ("Maximum difference accepted: %" G_GUINT64_FORMAT " levels", accepted_diff);
+          accepted_pixels = g_key_file_get_uint64 (keyfile, "reftest", "accepted-diff-pixels", NULL);
+          g_test_message ("Different pixels accepted: %" G_GUINT64_FORMAT, accepted_pixels);
+          tolerated_diff = g_key_file_get_uint64 (keyfile, "reftest", "tolerated-diff-level", NULL);
+          g_test_message ("Maximum difference tolerated: %" G_GUINT64_FORMAT " levels", tolerated_diff);
+          tolerated_pixels = g_key_file_get_uint64 (keyfile, "reftest", "tolerated-diff-pixels", NULL);
+          g_test_message ("Different pixels tolerated: %" G_GUINT64_FORMAT, tolerated_pixels);
+        }
+
       g_test_message ("%u (out of %u) pixels differ from reference by up to %u levels",
                       pixels_changed, pixels, max_diff);
-      save_image (diff_image, ui_file, ".diff.png");
-      g_test_fail ();
+
+      if (max_diff > accepted_diff || pixels_changed > accepted_pixels)
+        save_image (diff_image, ui_file, ".diff.png");
+
+      if (max_diff <= accepted_diff && pixels_changed <= accepted_pixels)
+        g_test_message ("differences are within acceptable range");
+      else if (max_diff <= tolerated_diff && pixels_changed <= tolerated_pixels)
+        g_test_incomplete ("not right, but close enough");
+      else
+        g_test_fail ();
+
+      g_key_file_unref (keyfile);
+      g_free (keyfile_path);
     }
 
   remove_extra_css (provider);
diff --git a/testsuite/reftests/image-compare.c b/testsuite/reftests/image-compare.c
index 07bb79e4e0..714f4fcadc 100644
--- a/testsuite/reftests/image-compare.c
+++ b/testsuite/reftests/image-compare.c
@@ -41,7 +41,7 @@ main (int argc, char **argv)
   image1 = cairo_image_surface_create_from_png (argv[1]);
   image2 = cairo_image_surface_create_from_png (argv[2]);
 
-  diff = reftest_compare_surfaces (image1, image2);
+  diff = reftest_compare_surfaces (image1, image2, NULL, NULL, NULL);
 
   if (opt_filename && diff)
     cairo_surface_write_to_png (diff, opt_filename);