rename z offset to layer offset

src/layout/vec2.rs

@@ -56,6 +56,16 @@ impl Vec2 {
     pub const fn tuple(&self) -> (f32, f32) {
         (self.x, self.y)
     }
+
+    pub const fn with_x(mut self, x: f32) -> Self {
+        self.x = x;
+        self
+    }
+
+    pub const fn with_y(mut self, y: f32) -> Self {
+        self.y = y;
+        self
+    }
 }
 
 impl<T: const UiNum + Copy> const From<T> for Vec2 {