Add scale_factor to Application and Sandbox

src/application.rs

@@ -186,6 +186,21 @@ pub trait Application: Sized {
         Color::WHITE
     }
 
+    /// Returns the scale factor of the [`Application`].
+    ///
+    /// It can be used to dynamically control the size of the UI at runtime
+    /// (i.e. zooming).
+    ///
+    /// For instance, a scale factor of `2.0` will make widgets twice as big,
+    /// while a scale factor of `0.5` will shrink them to half their size.
+    ///
+    /// By default, it returns `1.0`.
+    ///
+    /// [`Application`]: trait.Application.html
+    fn scale_factor(&self) -> f64 {
+        1.0
+    }
+
     /// Runs the [`Application`].
     ///
     /// On native platforms, this method will take control of the current thread
@@ -272,6 +287,10 @@ where
     fn background_color(&self) -> Color {
         self.0.background_color()
     }
+
+    fn scale_factor(&self) -> f64 {
+        self.0.scale_factor()
+    }
 }
 
 #[cfg(target_arch = "wasm32")]

src/sandbox.rs

@@ -130,12 +130,27 @@ pub trait Sandbox {
     ///
     /// By default, it returns [`Color::WHITE`].
     ///
-    /// [`Application`]: trait.Application.html
+    /// [`Sandbox`]: trait.Sandbox.html
     /// [`Color::WHITE`]: struct.Color.html#const.WHITE
     fn background_color(&self) -> Color {
         Color::WHITE
     }
 
+    /// Returns the scale factor of the [`Sandbox`].
+    ///
+    /// It can be used to dynamically control the size of the UI at runtime
+    /// (i.e. zooming).
+    ///
+    /// For instance, a scale factor of `2.0` will make widgets twice as big,
+    /// while a scale factor of `0.5` will shrink them to half their size.
+    ///
+    /// By default, it returns `1.0`.
+    ///
+    /// [`Sandbox`]: trait.Sandbox.html
+    fn scale_factor(&self) -> f64 {
+        1.0
+    }
+
     /// Runs the [`Sandbox`].
     ///
     /// On native platforms, this method will take control of the current thread
@@ -185,4 +200,8 @@ where
     fn background_color(&self) -> Color {
         T::background_color(self)
     }
+
+    fn scale_factor(&self) -> f64 {
+        T::scale_factor(self)
+    }
 }