On X11, filter out tiny device mouse events

Usually, if mouse events are equal to (0, 0) we filter them out.
However, if the event is very close to zero it will still be given to
the user. In some cases this can be caused by bad float math on the X11
server side.

Fix it by filtering absolute values smaller than floating point epsilon.

Signed-off-by: John Nunley <dev@notgull.net>
Closes: #3500

src/platform_impl/linux/x11/util/mod.rs

@@ -15,13 +15,15 @@ mod icon;
 mod input;
 pub mod keys;
 pub(crate) mod memory;
+mod mouse;
 mod randr;
 mod window_property;
 mod wm;
 mod xmodmap;
 
 pub use self::{
-    cursor::*, geometry::*, hint::*, input::*, window_property::*, wm::*, xmodmap::ModifierKeymap,
+    cursor::*, geometry::*, hint::*, input::*, mouse::*, window_property::*, wm::*,
+    xmodmap::ModifierKeymap,
 };
 
 use super::{atoms::*, ffi, VoidCookie, X11Error, XConnection, XError};

src/platform_impl/linux/x11/util/mouse.rs

@@ -0,0 +1,52 @@
+//! Utilities for handling mouse events.
+
+/// Recorded mouse delta designed to filter out noise.
+pub struct Delta<T> {
+    x: T,
+    y: T,
+}
+
+impl<T: Default> Default for Delta<T> {
+    fn default() -> Self {
+        Self {
+            x: Default::default(),
+            y: Default::default(),
+        }
+    }
+}
+
+impl<T: Default> Delta<T> {
+    pub(crate) fn set_x(&mut self, x: T) {
+        self.x = x;
+    }
+
+    pub(crate) fn set_y(&mut self, y: T) {
+        self.y = y;
+    }
+}
+
+macro_rules! consume {
+    ($this:expr, $ty:ty) => {{
+        let this = $this;
+        let (x, y) = match (this.x.abs() < <$ty>::EPSILON, this.y.abs() < <$ty>::EPSILON) {
+            (true, true) => return None,
+            (true, false) => (this.x, 0.0),
+            (false, true) => (0.0, this.y),
+            (false, false) => (this.x, this.y),
+        };
+
+        Some((x, y))
+    }};
+}
+
+impl Delta<f32> {
+    pub(crate) fn consume(self) -> Option<(f32, f32)> {
+        consume!(self, f32)
+    }
+}
+
+impl Delta<f64> {
+    pub(crate) fn consume(self) -> Option<(f64, f64)> {
+        consume!(self, f64)
+    }
+}