[librsvg: 1/5] compare_surfaces: set the alpha of the diff always to opaque

[Federico Mena Quintero <federico src gnome org>]

commit 660f01f5f611197f61ed4994457a5ee51b2f0907
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed Aug 19 18:17:27 2020 -0500

    compare_surfaces: set the alpha of the diff always to opaque
    
    This was missing in the port from the C code; no wonder the diffs were
    always fully transparent.

 librsvg_crate/tests/utils/compare_surfaces.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/librsvg_crate/tests/utils/compare_surfaces.rs b/librsvg_crate/tests/utils/compare_surfaces.rs
index 91a694741..0a6e48e2d 100644
--- a/librsvg_crate/tests/utils/compare_surfaces.rs
+++ b/librsvg_crate/tests/utils/compare_surfaces.rs
@@ -103,13 +103,15 @@ pub fn compare_surfaces(
                     pixel_diff.b = pixel_diff.a;
                 }
 
+                pixel_diff.a = 255;
+
                 diff_data.set_pixel(diff_stride, pixel_diff, xa, ya);
             } else {
                 let black = Pixel {
                     r: 0,
                     g: 0,
                     b: 0,
-                    a: 0,
+                    a: 255,
                 };
                 diff_data.set_pixel(diff_stride, black, xa, ya);
             }