Add Context::set_pixels_per_point to control the scale of the UI

CHANGELOG.md

@@ -13,7 +13,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 * Add `egui::plot::Plot` to plot some 2D data.
 * Add `Ui::hyperlink_to(label, url)`.
-* Sliders can now have a value prefix and suffix (e.g. "°" as a unit).
+* Sliders can now have a value prefix and suffix (e.g. the suffix `"°"` works like a unit).
+* `Context::set_pixels_per_point` to control the scale of the UI.
 
 ### Changed 🔧
 

egui/src/context.rs

@@ -388,7 +388,6 @@ impl Context {
     }
 
     /// Will become active at the start of the next frame.
-    /// `pixels_per_point` will be ignored (overwritten at start of each frame with the contents of input)
     pub fn set_fonts(&self, font_definitions: FontDefinitions) {
         self.memory().options.font_definitions = font_definitions;
     }
@@ -429,6 +428,15 @@ impl Context {
         self.input.pixels_per_point()
     }
 
+    /// Set the number of physical pixels for each logical point.
+    /// Will become active at the start of the next frame.
+    ///
+    /// Note that this may be overwritten by input from the integration via [`RawInput::pixels_per_point`].
+    /// For instance, when using `egui_web` the browsers native zoom level will always be used.
+    pub fn set_pixels_per_point(&self, pixels_per_point: f32) {
+        self.memory().new_pixels_per_point = Some(pixels_per_point);
+    }
+
     /// Useful for pixel-perfect rendering
     pub(crate) fn round_to_pixel(&self, point: f32) -> f32 {
         let pixels_per_point = self.pixels_per_point();
@@ -493,7 +501,12 @@ impl Context {
     fn begin_frame_mut(&mut self, new_raw_input: RawInput) {
         self.memory().begin_frame(&self.input, &new_raw_input);
 
-        self.input = std::mem::take(&mut self.input).begin_frame(new_raw_input);
+        let mut input = std::mem::take(&mut self.input);
+        if let Some(new_pixels_per_point) = self.memory().new_pixels_per_point.take() {
+            input.pixels_per_point = new_pixels_per_point;
+        }
+
+        self.input = input.begin_frame(new_raw_input);
         self.frame_state.lock().begin_frame(&self.input);
 
         let font_definitions = self.memory().options.font_definitions.clone();

egui/src/data/input.rs

@@ -27,6 +27,7 @@ pub struct RawInput {
 
     /// Also known as device pixel ratio, > 1 for HDPI screens.
     /// If text looks blurry on high resolution screens, you probably forgot to set this.
+    /// Set this the first frame, whenever it changes, or just on every frame.
     pub pixels_per_point: Option<f32>,
 
     /// Monotonically increasing time, in seconds. Relative to whatever. Used for animations.
@@ -68,9 +69,9 @@ impl RawInput {
         RawInput {
             scroll_delta: std::mem::take(&mut self.scroll_delta),
             screen_size: self.screen_size,
-            screen_rect: self.screen_rect,
-            pixels_per_point: self.pixels_per_point,
-            time: self.time,
+            screen_rect: self.screen_rect.take(),
+            pixels_per_point: self.pixels_per_point.take(),
+            time: self.time.take(),
             predicted_dt: self.predicted_dt,
             modifiers: self.modifiers,
             events: std::mem::take(&mut self.events),

egui/src/memory.rs

@@ -20,6 +20,9 @@ use epaint::color::{Color32, Hsva};
 pub struct Memory {
     pub(crate) options: Options,
 
+    /// new scale that will be applied at the start of the next frame
+    pub(crate) new_pixels_per_point: Option<f32>,
+
     #[cfg_attr(feature = "persistence", serde(skip))]
     pub(crate) interaction: Interaction,
 

egui_demo_lib/src/wrap_app.rs

@@ -251,11 +251,13 @@ impl BackendPanel {
 
         self.frame_history.ui(ui);
 
-        if !frame.is_web() {
-            // web browsers have their own way of zooming, which egui_web respects
+        // For instance: `egui_web` sets `pixels_per_point` every frame to force
+        // egui to use the same scale as the web zoom factor.
+        let integration_controls_pixels_per_point = ui.input().raw.pixels_per_point.is_some();
+        if !integration_controls_pixels_per_point {
             ui.separator();
             if let Some(new_pixels_per_point) = self.pixels_per_point_ui(ui, frame.info()) {
-                frame.set_pixels_per_point(new_pixels_per_point);
+                ui.ctx().set_pixels_per_point(new_pixels_per_point);
             }
         }
 

egui_glium/src/backend.rs

@@ -192,11 +192,16 @@ pub fn run(mut app: Box<dyn epi::App>) -> ! {
 
     event_loop.run(move |event, _, control_flow| {
         let mut redraw = || {
+            let pixels_per_point = input_state
+                .raw
+                .pixels_per_point
+                .unwrap_or_else(|| ctx.pixels_per_point());
+
             let frame_start = Instant::now();
             input_state.raw.time = Some(start_time.elapsed().as_nanos() as f64 * 1e-9);
             input_state.raw.screen_rect = Some(Rect::from_min_size(
                 Default::default(),
-                screen_size_in_pixels(&display) / input_state.raw.pixels_per_point.unwrap(),
+                screen_size_in_pixels(&display) / pixels_per_point,
             ));
 
             ctx.begin_frame(input_state.raw.take());
@@ -225,16 +230,7 @@ pub fn run(mut app: Box<dyn epi::App>) -> ! {
             );
 
             {
-                let epi::backend::AppOutput {
-                    quit,
-                    window_size,
-                    pixels_per_point,
-                } = app_output;
-
-                if let Some(pixels_per_point) = pixels_per_point {
-                    // User changed GUI scale
-                    input_state.raw.pixels_per_point = Some(pixels_per_point);
-                }
+                let epi::backend::AppOutput { quit, window_size } = app_output;
 
                 if let Some(window_size) = window_size {
                     display.gl_window().window().set_inner_size(
@@ -283,7 +279,13 @@ pub fn run(mut app: Box<dyn epi::App>) -> ! {
             glutin::event::Event::RedrawRequested(_) if !cfg!(windows) => redraw(),
 
             glutin::event::Event::WindowEvent { event, .. } => {
-                input_to_egui(event, clipboard.as_mut(), &mut input_state, control_flow);
+                input_to_egui(
+                    ctx.pixels_per_point(),
+                    event,
+                    clipboard.as_mut(),
+                    &mut input_state,
+                    control_flow,
+                );
                 display.gl_window().window().request_redraw(); // TODO: ask egui if the events warrants a repaint instead
             }
             glutin::event::Event::LoopDestroyed => {

egui_glium/src/lib.rs

@@ -46,6 +46,7 @@ impl GliumInputState {
 }
 
 pub fn input_to_egui(
+    pixels_per_point: f32,
     event: glutin::event::WindowEvent<'_>,
     clipboard: Option<&mut ClipboardContext>,
     input_state: &mut GliumInputState,
@@ -54,6 +55,9 @@ pub fn input_to_egui(
     use glutin::event::WindowEvent;
     match event {
         WindowEvent::CloseRequested | WindowEvent::Destroyed => *control_flow = ControlFlow::Exit,
+        WindowEvent::ScaleFactorChanged { scale_factor, .. } => {
+            input_state.raw.pixels_per_point = Some(scale_factor as f32);
+        }
         WindowEvent::MouseInput { state, button, .. } => {
             if let Some(pos_in_points) = input_state.pointer_pos_in_points {
                 if let Some(button) = translate_mouse_button(button) {
@@ -71,8 +75,8 @@ pub fn input_to_egui(
             ..
         } => {
             let pos_in_points = pos2(
-                pos_in_pixels.x as f32 / input_state.raw.pixels_per_point.unwrap(),
-                pos_in_pixels.y as f32 / input_state.raw.pixels_per_point.unwrap(),
+                pos_in_pixels.x as f32 / pixels_per_point,
+                pos_in_pixels.y as f32 / pixels_per_point,
             );
             input_state.pointer_pos_in_points = Some(pos_in_points);
             input_state

egui_web/src/backend.rs

@@ -91,7 +91,7 @@ impl WebInput {
     pub fn new_frame(&mut self, canvas_size: egui::Vec2) -> egui::RawInput {
         egui::RawInput {
             screen_rect: Some(egui::Rect::from_min_size(Default::default(), canvas_size)),
-            pixels_per_point: Some(native_pixels_per_point()),
+            pixels_per_point: Some(native_pixels_per_point()), // We ALWAYS use the native pixels-per-point
             time: Some(now_sec()),
             ..self.raw.take()
         }
@@ -223,7 +223,6 @@ impl AppRunner {
             let epi::backend::AppOutput {
                 quit: _,        // Can't quit a web page
                 window_size: _, // Can't resize a web page
-                pixels_per_point: _, // Can't zoom from within the app (we respect the web browser's zoom level)
             } = app_output;
         }
 

epi/src/lib.rs

@@ -144,10 +144,9 @@ impl<'a> Frame<'a> {
         self.0.output.window_size = Some(size);
     }
 
-    /// Change the `pixels_per_point` of [`egui`] to this next frame.
-    pub fn set_pixels_per_point(&mut self, pixels_per_point: f32) {
-        self.0.output.pixels_per_point = Some(pixels_per_point);
-    }
+    /// Use [`egui::Context::set_pixels_per_point`] instead
+    #[deprecated = "Use egui::Context::set_pixels_per_point instead"]
+    pub fn set_pixels_per_point(&mut self, _: f32) {}
 
     /// If you need to request a repaint from another thread, clone this and send it to that other thread.
     pub fn repaint_signal(&self) -> std::sync::Arc<dyn RepaintSignal> {
@@ -367,8 +366,5 @@ pub mod backend {
 
         /// Set to some size to resize the outer window (e.g. glium window) to this size.
         pub window_size: Option<egui::Vec2>,
-
-        /// If the app sets this, change the `pixels_per_point` of [`egui`] to this next frame.
-        pub pixels_per_point: Option<f32>,
     }
 }