fix: clamp mouse position just below output size

src/input/mod.rs

@@ -703,11 +703,11 @@ impl State {
 
                     position.x = position.x.clamp(
                         output_geometry.loc.x as f64,
-                        (output_geometry.loc.x + output_geometry.size.w) as f64,
+                        ((output_geometry.loc.x + output_geometry.size.w) as f64).next_lower(), // FIXME: Replace with f64::next_down when stable
                     );
                     position.y = position.y.clamp(
                         output_geometry.loc.y as f64,
-                        (output_geometry.loc.y + output_geometry.size.h) as f64,
+                        ((output_geometry.loc.y + output_geometry.size.h) as f64).next_lower(), // FIXME: Replace with f64::next_down when stable
                     );
 
                     // If confined, don't move pointer if it would go outside surface or region
@@ -2337,3 +2337,32 @@ fn mapped_output_for_device<'a, D: Device + 'static>(
     };
     map_to_output.or_else(|| state.shell.builtin_output())
 }
+
+// FIXME: When f64::next_down reaches stable rust, use that instead
+trait NextDown {
+    fn next_lower(self) -> Self;
+}
+
+impl NextDown for f64 {
+    fn next_lower(self) -> Self {
+        // We must use strictly integer arithmetic to prevent denormals from
+        // flushing to zero after an arithmetic operation on some platforms.
+        const NEG_TINY_BITS: u64 = 0x8000_0000_0000_0001; // Smallest (in magnitude) negative f64.
+        const CLEAR_SIGN_MASK: u64 = 0x7fff_ffff_ffff_ffff;
+
+        let bits = self.to_bits();
+        if self.is_nan() || bits == Self::NEG_INFINITY.to_bits() {
+            return self;
+        }
+
+        let abs = bits & CLEAR_SIGN_MASK;
+        let next_bits = if abs == 0 {
+            NEG_TINY_BITS
+        } else if bits == abs {
+            bits - 1
+        } else {
+            bits + 1
+        };
+        Self::from_bits(next_bits)
+    }
+}