Fix theme preference not being restored correctly

Using `set_visuals(Visuals::dark())` in `main()` somehow interfered
badly with the theme switching code such that a light theme was not
restored properly.

Instead, the correct function to set the theme on startup is
`set_theme()` and we should pass in the saved perference instead of
hard-coding dark-mode.

With these changes, all of the theme preferences work correctly and are
restored correctly.

Author: Rahix

src/main.rs

@@ -10,7 +10,7 @@ use crate::gui::{load_gui_settings, GuiCommand, MyApp, RIGHT_PANEL_WIDTH};
 use crate::io::{open_from_csv, save_to_csv, FileOptions};
 use crate::serial::{load_serial_settings, serial_devices_thread, serial_thread, Device};
 use crossbeam_channel::{select, Receiver, Sender};
-use eframe::egui::{vec2, ViewportBuilder, Visuals};
+use eframe::egui::{vec2, ViewportBuilder};
 use eframe::{egui, icon_data};
 use egui_plot::PlotPoint;
 use preferences::AppInfo;
@@ -349,7 +349,7 @@ fn main() {
             let mut fonts = egui::FontDefinitions::default();
             egui_phosphor::add_to_fonts(&mut fonts, egui_phosphor::Variant::Regular);
             ctx.egui_ctx.set_fonts(fonts);
-            ctx.egui_ctx.set_visuals(Visuals::dark());
+            ctx.egui_ctx.set_theme(gui_settings.theme_preference);
             egui_extras::install_image_loaders(&ctx.egui_ctx);
 
             let repaint_signal = ctx.egui_ctx.clone();

src/settings_window.rs

@@ -2,7 +2,7 @@ use crate::gui::GuiSettingsContainer;
 #[cfg(feature = "self_update")]
 use crate::update::{check_update, update};
 use eframe::egui;
-use eframe::egui::{Align2, InnerResponse, Vec2, Visuals};
+use eframe::egui::{Align2, InnerResponse, Vec2};
 use egui_theme_switch::ThemeSwitch;
 #[cfg(feature = "self_update")]
 use self_update::restart::restart;
@@ -32,7 +32,7 @@ pub fn settings_window(
                     {
                         ui.ctx().set_theme(gui_conf.theme_preference);
                     };
-                    gui_conf.dark_mode = ui.visuals() == &Visuals::dark();
+                    gui_conf.dark_mode = ui.ctx().theme() == egui::Theme::Dark;
 
                     ui.end_row();
                     ui.end_row();