Add ui.drag_angle helper

egui/src/demos/app.rs

@@ -416,6 +416,7 @@ struct Widgets {
     count: usize,
     radio: usize,
     slider_value: f32,
+    angle: f32,
     single_line_text_input: String,
     multiline_text_input: String,
 }
@@ -427,6 +428,7 @@ impl Default for Widgets {
             radio: 0,
             count: 0,
             slider_value: 3.4,
+            angle: TAU / 8.0,
             single_line_text_input: "Hello World!".to_owned(),
             multiline_text_input: "Text can both be so wide that it needs a line break, but you can also add manual line break by pressing enter, creating new paragraphs.\nThis is the start of the next paragraph.\n\nClick me to edit me!".to_owned(),
         }
@@ -480,6 +482,15 @@ impl Widgets {
             }
         }
         ui.separator();
+        {
+            ui.label("An angle stored as radians, but edited in degrees:");
+            ui.horizontal_centered(|ui| {
+                ui.style_mut().item_spacing.x = 0.0;
+                ui.drag_angle(&mut self.angle);
+                ui.label(format!(" = {} radians", self.angle));
+            });
+        }
+        ui.separator();
 
         ui.horizontal(|ui| {
             ui.add(label!("Single line text input:"));

egui/src/paint/font.rs

@@ -211,6 +211,7 @@ impl Font {
             font.add_char(c);
         }
         font.add_char(REPLACEMENT_CHAR);
+        font.add_char('°');
 
         font
     }

egui/src/ui.rs

@@ -506,6 +506,22 @@ impl Ui {
     pub fn separator(&mut self) -> GuiResponse {
         self.add(Separator::new())
     }
+
+    /// Modify an angle. The given angle should be in radians, but is shown to the user in degrees.
+    /// The angle is NOT wrapped, so the user may select, for instance 720° = 2𝞃 = 4π
+    pub fn drag_angle(&mut self, radians: &mut f32) -> GuiResponse {
+        #![allow(clippy::float_cmp)]
+
+        let mut degrees = radians.to_degrees();
+        let response = self.add(DragValue::f32(&mut degrees).speed(1.0).suffix("°"));
+
+        // only touch `*radians` if we actually changed the degree value
+        if degrees != radians.to_degrees() {
+            *radians = degrees.to_radians();
+        }
+
+        response
+    }
 }
 
 /// # Adding Containers / Sub-uis:

egui/src/widgets.rs

@@ -552,11 +552,18 @@ impl Widget for Separator {
 pub struct DragValue<'a> {
     value: &'a mut f32,
     speed: f32,
+    prefix: String,
+    suffix: String,
 }
 
 impl<'a> DragValue<'a> {
     pub fn f32(value: &'a mut f32) -> Self {
-        DragValue { value, speed: 1.0 }
+        DragValue {
+            value,
+            speed: 1.0,
+            prefix: Default::default(),
+            suffix: Default::default(),
+        }
     }
 
     /// How much the value changes when dragged one point (logical pixel).
@@ -564,16 +571,30 @@ impl<'a> DragValue<'a> {
         self.speed = speed;
         self
     }
+
+    /// Show a prefix before the number, e.g. "x: "
+    pub fn prefix(mut self, prefix: impl ToString) -> Self {
+        self.prefix = prefix.to_string();
+        self
+    }
+
+    /// Add a suffix to the number, this can be e.g. a unit ("°" or " m")
+    pub fn suffix(mut self, suffix: impl ToString) -> Self {
+        self.suffix = suffix.to_string();
+        self
+    }
 }
 
 impl<'a> Widget for DragValue<'a> {
     fn ui(self, ui: &mut Ui) -> InteractInfo {
-        let Self { value, speed } = self;
+        let Self {
-        let speed_in_physical_pixels = speed / ui.input().pixels_per_point;
+            value,
-        let precision = (1.0 / speed_in_physical_pixels.abs())
+            speed,
-            .log10()
+            prefix,
-            .ceil()
+            suffix,
-            .max(0.0) as usize;
+        } = self;
+        let aim_rad = ui.input().physical_pixel_size(); // ui.input().aim_radius(); // TODO
+        let precision = (aim_rad / speed.abs()).log10().ceil().max(0.0) as usize;
         let value_text = format_with_minimum_precision(*value, precision);
 
         let kb_edit_id = ui.make_position_id().with("edit");
@@ -602,7 +623,7 @@ impl<'a> Widget for DragValue<'a> {
             }
             response.into()
         } else {
-            let button = Button::new(value_text)
+            let button = Button::new(format!("{}{}{}", prefix, value_text, suffix))
                 .sense(Sense::click_and_drag())
                 .text_style(TextStyle::Monospace);
             let response = ui.add(button);