[widgets] new widget: DragValue

egui/src/examples/app.rs

@@ -277,7 +277,7 @@ struct Widgets {
     checked: bool,
     count: usize,
     radio: usize,
-    slider_value: usize,
+    slider_value: f32,
     single_line_text_input: String,
     multiline_text_input: String,
 }
@@ -288,7 +288,7 @@ impl Default for Widgets {
             checked: true,
             radio: 0,
             count: 0,
-            slider_value: 100,
+            slider_value: 3.14,
             single_line_text_input: "Hello World!".to_owned(),
             multiline_text_input: "Text can both be so wide that it needs a linebreak, but you can also add manual linebreak by pressing enter, creating new paragraphs.\nThis is the start of the next paragraph.\n\nClick me to edit me!".to_owned(),
         }
@@ -330,10 +330,18 @@ impl Widgets {
             ui.add(label!("The button has been clicked {} times", self.count));
         });
 
-        ui.add(Slider::usize(&mut self.slider_value, 1..=1000).text("value"));
+        ui.add(
+            Slider::f32(&mut self.slider_value, -10.0..=10.0)
+                .text("value")
+                .precision(2),
+        );
         if ui.add(Button::new("Double it")).clicked {
-            self.slider_value *= 2;
+            self.slider_value *= 2.0;
         }
+        ui.horizontal(|ui| {
+            ui.label("drag this number:");
+            ui.add(DragValue::f32(&mut self.slider_value).speed(0.01));
+        });
 
         ui.horizontal(|ui| {
             ui.add(label!("Single line text input:"));

egui/src/widgets.rs

@@ -231,7 +231,7 @@ impl Button {
     pub fn sense(mut self, sense: Sense) -> Self {
         self.sense = sense;
         self
-}
+    }
 }
 
 impl Widget for Button {
@@ -506,3 +506,45 @@ impl Widget for Separator {
         ui.interact_hover(rect)
     }
 }
+
+// ----------------------------------------------------------------------------
+
+pub struct DragValue<'a> {
+    value: &'a mut f32,
+    speed: f32,
+}
+
+impl<'a> DragValue<'a> {
+    pub fn f32(value: &'a mut f32) -> Self {
+        DragValue { value, speed: 1.0 }
+    }
+
+    /// How much the value changes when dragged one point (logical pixel).
+    pub fn speed(mut self, speed: f32) -> Self {
+        self.speed = speed;
+        self
+    }
+}
+
+impl<'a> Widget for DragValue<'a> {
+    fn ui(self, ui: &mut Ui) -> InteractInfo {
+        let Self { value, speed } = self;
+        let speed_in_physical_pixels = speed / ui.input().pixels_per_point;
+        let precision = (1.0 / speed_in_physical_pixels.abs())
+            .log10()
+            .ceil()
+            .max(0.0) as usize;
+        let button = Button::new(format!("{:.*}", precision, *value)).sense(Sense::drag());
+        let interact = ui.add(button);
+        if interact.active {
+            let mdelta = ui.input().mouse.delta;
+            let delta_points = mdelta.x - mdelta.y; // Increase to the right and up
+            let delta_value = speed * delta_points;
+            if delta_value != 0.0 {
+                *value += delta_value;
+                *value = round_to_precision(*value, precision);
+            }
+        }
+        interact.into()
+    }
+}