Add widget egui::reset_button

egui/src/introspection.rs

@@ -65,8 +65,6 @@ impl paint::FontDefinitions {
                     .text(format!("{:?}", text_style)),
             );
         }
-        if ui.button("Reset fonts").clicked {
+        crate::reset_button(ui, self);
-            *self = Default::default();
-        }
     }
 }

egui/src/style.rs

@@ -345,9 +345,7 @@ use crate::{widgets::*, Ui};
 
 impl Style {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        if ui.button("Reset").clicked {
+        crate::reset_button(ui, self);
-            *self = Default::default();
-        }
 
         let Self {
             body_text_style,
@@ -371,9 +369,7 @@ impl Style {
 
 impl Spacing {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        if ui.button("Reset").clicked {
+        crate::reset_button(ui, self);
-            *self = Default::default();
-        }
 
         let Self {
             item_spacing,
@@ -404,15 +400,12 @@ impl Spacing {
 
 impl Interaction {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        if ui.button("Reset").clicked {
+        crate::reset_button(ui, self);
-            *self = Default::default();
-        }
 
         let Self {
             resize_grab_radius_side,
             resize_grab_radius_corner,
         } = self;
-
         ui.add(Slider::f32(resize_grab_radius_side, 0.0..=20.0).text("resize_grab_radius_side"));
         ui.add(
             Slider::f32(resize_grab_radius_corner, 0.0..=20.0).text("resize_grab_radius_corner"),
@@ -422,9 +415,7 @@ impl Interaction {
 
 impl Widgets {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        if ui.button("Reset").clicked {
+        crate::reset_button(ui, self);
-            *self = Default::default();
-        }
 
         let Self {
             active,
@@ -471,9 +462,7 @@ impl WidgetVisuals {
 
 impl Visuals {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        if ui.button("Reset").clicked {
+        crate::reset_button(ui, self);
-            *self = Default::default();
-        }
 
         let Self {
             override_text_color: _,

egui/src/widgets/mod.rs

@@ -739,3 +739,14 @@ impl Widget for Separator {
         response
     }
 }
+
+// ----------------------------------------------------------------------------
+
+/// Show a button to reset a value to its default.
+/// The button is only enabled if the value does not already have its original value.
+pub fn reset_button<T: Default + PartialEq>(ui: &mut Ui, value: &mut T) {
+    let def = T::default();
+    if ui.add(Button::new("Reset").enabled(*value != def)).clicked {
+        *value = def;
+    }
+}

egui_demo_lib/src/apps/demo/demo_window.rs

@@ -106,7 +106,7 @@ impl DemoWindow {
 
 // ----------------------------------------------------------------------------
 
-#[derive(serde::Deserialize, serde::Serialize)]
+#[derive(PartialEq, serde::Deserialize, serde::Serialize)]
 #[serde(default)]
 struct ColorWidgets {
     srgba_unmul: [u8; 4],
@@ -129,9 +129,7 @@ impl Default for ColorWidgets {
 
 impl ColorWidgets {
     fn ui(&mut self, ui: &mut Ui) {
-        if ui.button("Reset").clicked {
+        egui::reset_button(ui, self);
-            *self = Default::default();
-        }
 
         ui.label("Egui lets you edit colors stored as either sRGBA or linear RGBA and with or without premultiplied alpha");
 

egui_demo_lib/src/apps/demo/sliders.rs

@@ -2,7 +2,7 @@ use egui::*;
 use std::f64::INFINITY;
 
 /// Showcase sliders
-#[derive(serde::Deserialize, serde::Serialize)]
+#[derive(PartialEq, serde::Deserialize, serde::Serialize)]
 #[serde(default)]
 pub struct Sliders {
     pub min: f64,
@@ -108,8 +108,6 @@ impl Sliders {
         ui.checkbox(smart_aim, "Smart Aim");
         ui.label("Smart Aim will guide you towards round values when you drag the slider so you you are more likely to hit 250 than 247.23");
 
-        if ui.button("Reset slider demo").clicked {
+        egui::reset_button(ui, self);
-            *self = Default::default();
-        }
     }
 }

egui_demo_lib/src/apps/fractal_clock.rs

@@ -1,7 +1,7 @@
 use egui::{containers::*, widgets::*, *};
 use std::f32::consts::TAU;
 
-#[derive(serde::Deserialize, serde::Serialize)]
+#[derive(PartialEq, serde::Deserialize, serde::Serialize)]
 #[serde(default)]
 pub struct FractalClock {
     paused: bool,
@@ -87,9 +87,8 @@ impl FractalClock {
         ui.add(Slider::f32(&mut self.length_factor, 0.0..=1.0).text("length factor"));
         ui.add(Slider::f32(&mut self.luminance_factor, 0.0..=1.0).text("luminance factor"));
         ui.add(Slider::f32(&mut self.width_factor, 0.0..=1.0).text("width factor"));
-        if ui.button("Reset").clicked {
+
-            *self = Default::default();
+        egui::reset_button(ui, self);
-        }
 
         ui.add(
             Hyperlink::new("http://www.dqd.com/~mayoff/programs/FractalClock/")