Introduce Cursor type in canvas

wgpu/src/widget/canvas/cursor.rs

@@ -0,0 +1,50 @@
+use iced_native::{Point, Rectangle};
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Cursor {
+    Available(Point),
+    Unavailable,
+}
+
+impl Cursor {
+    // TODO: Remove this once this type is used in `iced_native` to encode
+    // proper cursor availability
+    pub(crate) fn from_window_position(position: Point) -> Self {
+        if position.x < 0.0 || position.y < 0.0 {
+            Cursor::Unavailable
+        } else {
+            Cursor::Available(position)
+        }
+    }
+
+    pub fn position(&self) -> Option<Point> {
+        match self {
+            Cursor::Available(position) => Some(*position),
+            Cursor::Unavailable => None,
+        }
+    }
+
+    pub fn relative_position(&self, bounds: &Rectangle) -> Option<Point> {
+        match self {
+            Cursor::Available(position) => {
+                Some(Point::new(position.x - bounds.x, position.y - bounds.y))
+            }
+            _ => None,
+        }
+    }
+
+    pub fn internal_position(&self, bounds: &Rectangle) -> Option<Point> {
+        if self.is_over(bounds) {
+            self.relative_position(bounds)
+        } else {
+            None
+        }
+    }
+
+    pub fn is_over(&self, bounds: &Rectangle) -> bool {
+        match self {
+            Cursor::Available(position) => bounds.contains(*position),
+            Cursor::Unavailable => false,
+        }
+    }
+}