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

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,