[librsvg: 2/14] Add a format check to SharedImageSurface::new()

[Federico Mena Quintero <federico src gnome org>]

commit 45c7dd7991965e07b2ba84898a92fd1f3f594763
Author: Ivan Molodetskikh <yalterz gmail com>
Date:   Sun Jul 15 13:14:28 2018 +0300

    Add a format check to SharedImageSurface::new()

 rsvg_internals/src/surface_utils/shared_surface.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/rsvg_internals/src/surface_utils/shared_surface.rs 
b/rsvg_internals/src/surface_utils/shared_surface.rs
index fa5d0b04..088c642d 100644
--- a/rsvg_internals/src/surface_utils/shared_surface.rs
+++ b/rsvg_internals/src/surface_utils/shared_surface.rs
@@ -52,9 +52,13 @@ impl SharedImageSurface {
     /// Creates a `SharedImageSurface` from a unique `ImageSurface`.
     ///
     /// # Panics
-    /// Panics if the `ImageSurface` is not unique, that is, its reference count isn't 1.
+    /// Panics if the surface format isn't `ARgb32` and if the surface is not unique, that is, its
+    /// reference count isn't 1.
     #[inline]
     pub fn new(surface: ImageSurface) -> Result<Self, cairo::Status> {
+        // get_pixel() assumes ARgb32.
+        assert_eq!(surface.get_format(), cairo::Format::ARgb32);
+
         let reference_count =
             unsafe { cairo_sys::cairo_surface_get_reference_count(surface.to_raw_none()) };
         assert_eq!(reference_count, 1);