[librsvg: 3/5] Allow to configure the test tolerance

[Federico Mena Quintero <federico src gnome org>]

commit 27007dce0a388847b3defbc11fe5ba725d5811d9
Author: Sven Neumann <sven svenfoo org>
Date:   Sun Sep 20 22:42:31 2020 +0200

    Allow to configure the test tolerance
    
    If RSVG_TEST_TOLERANCE is set the number of pixels that the resulting
    image may differ from the reference result is taken from this environment
    variable.

 tests/rsvg-test.c | 37 +++++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)
---
diff --git a/tests/rsvg-test.c b/tests/rsvg-test.c
index 4f935bb1..55be7547 100644
--- a/tests/rsvg-test.c
+++ b/tests/rsvg-test.c
@@ -212,6 +212,28 @@ test_tolerate (const gchar *message)
 // offset.
 #define FRAME_SIZE 47
 
+G_GNUC_CONST static unsigned int
+tolerable_difference (void)
+{
+    const gchar *env = g_getenv ("RSVG_TEST_TOLERANCE");
+    if (env)
+       return strtoul (env, NULL, 10);
+
+#ifdef __x86_64__
+    return 2;
+#else
+    /* https://gitlab.gnome.org/GNOME/librsvg/issues/178,
+     * https://gitlab.gnome.org/GNOME/librsvg/issues/366 */
+    return 20;
+#endif
+}
+
+G_GNUC_CONST static unsigned int
+allowed_difference (void)
+{
+    return 2;
+}
+
 static void
 rsvg_cairo_check (gconstpointer data)
 {
@@ -277,26 +299,17 @@ rsvg_cairo_check (gconstpointer data)
                         width_a, height_a, width_b, height_b);
     }
     else {
-#ifdef __x86_64__
-       const unsigned int MAX_DIFF = 2;
-#else
-        /* https://gitlab.gnome.org/GNOME/librsvg/issues/178,
-         * https://gitlab.gnome.org/GNOME/librsvg/issues/366 */
-       const unsigned int MAX_DIFF = 20;
-#endif
-       const unsigned int WARN_DIFF = 2;
-
        surface_diff = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
                                                   dimensions.width, dimensions.height);
 
        test_utils_compare_surfaces (surface_a, surface_b, surface_diff, &result);
 
-       if (result.pixels_changed && result.max_diff > MAX_DIFF) {
+       if (result.pixels_changed && result.max_diff > tolerable_difference ()) {
             g_test_fail ();
             save_image (surface_diff, test_file_base, "-diff.png");
        }
-        else if (result.pixels_changed && result.max_diff > WARN_DIFF) {
-            test_tolerate ("not the same as x86_64, but giving it the benefit of the doubt");
+        else if (result.pixels_changed && result.max_diff > allowed_difference ()) {
+            test_tolerate ("not perfect, but somewhat tolerable");
             save_image (surface_diff, test_file_base, "-diff.png");
        }