Add scale_factor to Application and Sandbox

winit/src/application.rs

@@ -84,6 +84,21 @@ pub trait Application: Program {
     fn background_color(&self) -> Color {
         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 an [`Application`] with an executor, compositor, and the provided
@@ -124,6 +139,7 @@ pub fn run<A, E, C>(
     let mut title = application.title();
     let mut mode = application.mode();
     let mut background_color = application.background_color();
+    let mut scale_factor = application.scale_factor();
 
     let window = settings
         .window
@@ -138,7 +154,7 @@ pub fn run<A, E, C>(
     let physical_size = window.inner_size();
     let mut viewport = Viewport::with_physical_size(
         Size::new(physical_size.width, physical_size.height),
-        window.scale_factor(),
+        window.scale_factor() * scale_factor,
     );
     let mut resized = false;
 
@@ -208,6 +224,20 @@ pub fn run<A, E, C>(
 
                 // Update background color
                 background_color = program.background_color();
+
+                // Update scale factor
+                let new_scale_factor = program.scale_factor();
+
+                if scale_factor != new_scale_factor {
+                    let size = window.inner_size();
+
+                    viewport = Viewport::with_physical_size(
+                        Size::new(size.width, size.height),
+                        window.scale_factor() * new_scale_factor,
+                    );
+
+                    scale_factor = new_scale_factor;
+                }
             }
 
             window.request_redraw();
@@ -259,6 +289,7 @@ pub fn run<A, E, C>(
             handle_window_event(
                 &window_event,
                 &window,
+                scale_factor,
                 control_flow,
                 &mut modifiers,
                 &mut viewport,
@@ -286,6 +317,7 @@ pub fn run<A, E, C>(
 pub fn handle_window_event(
     event: &winit::event::WindowEvent<'_>,
     window: &winit::window::Window,
+    scale_factor: f64,
     control_flow: &mut winit::event_loop::ControlFlow,
     modifiers: &mut winit::event::ModifiersState,
     viewport: &mut Viewport,
@@ -298,8 +330,10 @@ pub fn handle_window_event(
         WindowEvent::Resized(new_size) => {
             let size = Size::new(new_size.width, new_size.height);
 
-            *viewport =
-                Viewport::with_physical_size(size, window.scale_factor());
+            *viewport = Viewport::with_physical_size(
+                size,
+                window.scale_factor() * scale_factor,
+            );
             *resized = true;
         }
         WindowEvent::CloseRequested => {