From 159e057a2881dd27c6a94fe1d1317b98eb4ef895 Mon Sep 17 00:00:00 2001
From: debarghaya <175645893+GhostMitra@users.noreply.github.com>
Date: Mon, 12 Oct 2026 00:51:23 +0530
Subject: [PATCH] Web & UI: resolve system theme preference and default web to
 system theme

---
 apps/gridcraft-web/src/web.rs |  1 +
 contributors/people.toml      |  4 ++++
 crates/ui-egui/src/theme.rs   | 15 +++++++++++++++
 crates/ui-egui/src/widgets.rs | 28 ++++++++++++++++++++++++++++
 4 files changed, 48 insertions(+)

diff --git a/apps/gridcraft-web/src/web.rs b/apps/gridcraft-web/src/web.rs
index 8b1e51d..a8b597d 100644
--- a/apps/gridcraft-web/src/web.rs
+++ b/apps/gridcraft-web/src/web.rs
@@ -38,6 +38,7 @@ pub fn start() {
                         let _ = session.execute("file.new", serde_json::json!({"sample": "sales"}));
                     }
                     let mut app = SheetApp::new(session, services(inbox.clone(), cc.egui_ctx.clone()));
+                    app.ui.system_theme = true;
                     // Follow the browser's language, except a CJK one: the web build has no system
                     // CJK fonts (none are bundled), so that interface would render as tofu.
                     let browser = gridcraft_ui_egui::i18n::Language::system();
diff --git a/contributors/people.toml b/contributors/people.toml
index 7b69da3..681a4dd 100644
--- a/contributors/people.toml
+++ b/contributors/people.toml
@@ -50,3 +50,7 @@ sync_github_name = false
 
 [people.Losminek]
 sync_github_name = true
+
+[people.GhostMitra]
+sync_github_name = true
+
diff --git a/crates/ui-egui/src/theme.rs b/crates/ui-egui/src/theme.rs
index 6774154..e408a29 100644
--- a/crates/ui-egui/src/theme.rs
+++ b/crates/ui-egui/src/theme.rs
@@ -142,6 +142,21 @@ impl Tokens {
     }
 }
 
+/// Resolves an [`egui::ThemePreference`] against the context's system theme.
+pub fn resolve_theme(pref: egui::ThemePreference, ctx: &egui::Context) -> egui::Theme {
+    match pref {
+        egui::ThemePreference::System => {
+            if ctx.input(|i| i.raw.system_theme == Some(egui::Theme::Dark)) {
+                egui::Theme::Dark
+            } else {
+                egui::Theme::Light
+            }
+        }
+        egui::ThemePreference::Light => egui::Theme::Light,
+        egui::ThemePreference::Dark => egui::Theme::Dark,
+    }
+}
+
 pub const UI: &str = "ui";
 pub const UI_BOLD: &str = "ui-bold";
 pub const CELL: &str = "cell";
diff --git a/crates/ui-egui/src/widgets.rs b/crates/ui-egui/src/widgets.rs
index a006c6b..5220f04 100644
--- a/crates/ui-egui/src/widgets.rs
+++ b/crates/ui-egui/src/widgets.rs
@@ -284,3 +284,31 @@ pub fn notice_bar(app: &mut SheetApp, ui: &mut Ui) {
         app.notice = None;
     }
 }
+
+/// Turn a monochrome image (black on white) into an alpha mask tinted with the active text color.
+pub fn raster_to_alpha_mask(pixels: &mut [egui::Color32]) {
+    for p in pixels.iter_mut() {
+        // Darkness of source becomes the opacity
+        let darkness = 255u8.saturating_sub(p.r());
+        // Pure white glyph with variable alpha
+        *p = egui::Color32::from_rgba_unmultiplied(255, 255, 255, darkness);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_raster_to_alpha_mask() {
+        let mut pixels = vec![
+            egui::Color32::WHITE,                   // r=255 -> darkness=0 -> alpha=0
+            egui::Color32::BLACK,                   // r=0 -> darkness=255 -> alpha=255
+            egui::Color32::from_rgb(100, 100, 100), // r=100 -> darkness=155 -> alpha=155
+        ];
+        raster_to_alpha_mask(&mut pixels);
+        assert_eq!(pixels[0], egui::Color32::from_rgba_unmultiplied(255, 255, 255, 0));
+        assert_eq!(pixels[1], egui::Color32::from_rgba_unmultiplied(255, 255, 255, 255));
+        assert_eq!(pixels[2], egui::Color32::from_rgba_unmultiplied(255, 255, 255, 155));
+    }
+}