craft-texture: compare images by value whether or not the buffer is shared

Image equality no longer short-cuts on a shared buffer. An image holding
NaN compared equal to its clone but unequal to the same image built
again; it is now unequal to both, as f32 comparison gives.

crates/texture/src/lib.rs

@@ -134,9 +134,11 @@ pub struct Image {
     data: Arc<Vec<f32>>,
 }
 
+/// Images are equal when their size, kind and floats are equal. Floats compare as `f32` does, so
+/// an image holding NaN is unequal to every image, its clones included.
 impl PartialEq for Image {
     fn eq(&self, o: &Image) -> bool {
-        self.w == o.w && self.h == o.h && self.kind == o.kind && (Arc::ptr_eq(&self.data, &o.data) || self.data == o.data)
+        self.w == o.w && self.h == o.h && self.kind == o.kind && self.data == o.data
     }
 }
 
@@ -739,6 +741,18 @@ mod tests {
         }
     }
 
+    #[test]
+    fn equality_does_not_depend_on_buffer_sharing() {
+        let img = Image::filled(2, 1, Kind::Gray, [f32::NAN; 4]);
+        let rebuilt = Image::filled(2, 1, Kind::Gray, [f32::NAN; 4]);
+        // NaN pixels compare unequal as floats do, whether or not the buffer is shared.
+        assert_ne!(img, rebuilt);
+        assert_ne!(img, img.clone());
+        let finite = Image::filled(2, 1, Kind::Gray, [0.5; 4]);
+        assert_eq!(finite, finite.clone());
+        assert_eq!(finite, Image::filled(2, 1, Kind::Gray, [0.5; 4]));
+    }
+
     #[test]
     fn box_shrink_averages_large_hdr_values() {
         let img = Image::filled(2, 2, Kind::Color, [f32::MAX, -f32::MAX, 1.0, 1.0]);