feat: add kraft paper tiled background texture for comfortable reading

src/reader.rs

@@ -25,6 +25,7 @@ pub struct ReaderAction {
     pub go_back: bool,
     pub toggle_theme: bool,
     pub toggle_bookmark: bool,
+    pub toggle_kraft_bg: bool,
     pub page_next: bool,
     pub page_prev: bool,
 }
@@ -38,11 +39,14 @@ pub fn reading_view(
     font_size: &mut f32,
     theme: &Theme,
     _file_path: &str,
+    kraft_texture: Option<&egui::TextureHandle>,
+    use_kraft_bg: bool,
 ) -> ReaderAction {
     let mut action = ReaderAction {
         go_back: false,
         toggle_theme: false,
         toggle_bookmark: false,
+        toggle_kraft_bg: false,
         page_next: false,
         page_prev: false,
     };
@@ -91,6 +95,10 @@ pub fn reading_view(
                     if ui.button("A⁺").on_hover_text("放大字体").clicked() {
                         *font_size = (*font_size + 2.0).min(48.0);
                     }
+                    let kraft_icon = if use_kraft_bg { "📄" } else { "📋" };
+                    if ui.button(kraft_icon).on_hover_text("牛皮纸背景").clicked() {
+                        action.toggle_kraft_bg = true;
+                    }
                     if ui.button("☰").on_hover_text("打开/关闭目录").clicked() {
                         *sidebar_open = !*sidebar_open;
                     }
@@ -163,6 +171,13 @@ pub fn reading_view(
         let available = ui.available_size();
         let (rect, response) = ui.allocate_at_least(available, egui::Sense::click());
 
+        // Draw kraft paper background if enabled
+        if use_kraft_bg {
+            if let Some(tex) = kraft_texture {
+                crate::texture::draw_tiled_bg(ui.painter(), rect, tex);
+            }
+        }
+
         // Add reading margins (inset)
         let inset = 24.0;
         let text_rect = egui::Rect::from_min_size(