math_app: extract toggle_button helper to reduce UI code duplication

src/widgets.rs

@@ -1,5 +1,6 @@
 use crate::misc::Offset;
-use egui::{Id, InnerResponse};
+use egui::{Button, Id, InnerResponse, Ui};
+use std::ops::BitXorAssign;
 
 /// Creates an area ontop of a widget with an y offset
 pub fn widgets_ontop<R>(
@@ -15,3 +16,13 @@ pub fn widgets_ontop<R>(
 
     area.show(ui.ctx(), |ui| add_contents(ui))
 }
+
+/// A toggle button that XORs its state when clicked.
+/// Shows different hover text based on current state.
+pub fn toggle_button(ui: &mut Ui, state: &mut bool, label: &str, enabled_tip: &str, disabled_tip: &str) {
+    state.bitxor_assign(
+        ui.add(Button::new(label))
+            .on_hover_text(if *state { enabled_tip } else { disabled_tip })
+            .clicked(),
+    );
+}