diff --git a/cimery/crates/viewer/src/lib.rs b/cimery/crates/viewer/src/lib.rs
index 117229a..f53df9b 100644
--- a/cimery/crates/viewer/src/lib.rs
+++ b/cimery/crates/viewer/src/lib.rs
@@ -278,6 +278,27 @@ impl RenderState {
 
         // ── egui ──────────────────────────────────────────────────────────────
         let egui_ctx = egui::Context::default();
+
+        // Load Korean system font (Windows Malgun Gothic) for CJK support
+        {
+            let mut fonts = egui::FontDefinitions::default();
+            let font_path = "C:\\Windows\\Fonts\\malgun.ttf";
+            if let Ok(data) = std::fs::read(font_path) {
+                fonts.font_data.insert(
+                    "MalgunGothic".to_owned(),
+                    egui::FontData::from_owned(data),
+                );
+                // Insert as primary font (index 0) so Korean renders by default
+                for family in fonts.families.values_mut() {
+                    family.insert(0, "MalgunGothic".to_owned());
+                }
+                egui_ctx.set_fonts(fonts);
+                log::info!("Korean font loaded: {}", font_path);
+            } else {
+                log::warn!("Korean font not found at {}; UI labels will show boxes", font_path);
+            }
+        }
+
         let egui_state = egui_winit::State::new(
             egui_ctx.clone(),
             egui::ViewportId::ROOT,
@@ -408,35 +429,28 @@ impl RenderState {
                     ui.heading("교량 속성");
                     ui.separator();
 
-                    let prev = p.span_m;
-                    ui.label("경간 (m)");
-                    ui.add(egui::Slider::new(&mut p.span_m, 20.0..=80.0).step_by(1.0));
-                    if (p.span_m - prev).abs() > 0.001 { dirty = true; }
+                    // Helper: slider that auto-applies on drag release
+                    macro_rules! param_slider {
+                        ($label:expr, $val:expr, $range:expr, $step:expr) => {{
+                            ui.label($label);
+                            let r = ui.add(egui::Slider::new($val, $range).step_by($step));
+                            if r.drag_released() || r.lost_focus() { apply = true; dirty = true; }
+                            if r.changed() { dirty = true; }
+                        }};
+                    }
 
-                    let prev = p.girder_count;
-                    ui.label("거더 수");
-                    ui.add(egui::Slider::new(&mut p.girder_count, 3..=7));
-                    if p.girder_count != prev { dirty = true; }
-
-                    let prev = p.girder_spacing;
-                    ui.label("c/c 간격 (mm)");
-                    ui.add(egui::Slider::new(&mut p.girder_spacing, 1_500.0..=4_000.0).step_by(100.0));
-                    if (p.girder_spacing - prev).abs() > 1.0 { dirty = true; }
-
-                    let prev = p.girder_height;
-                    ui.label("거더 높이 (mm)");
-                    ui.add(egui::Slider::new(&mut p.girder_height, 1_000.0..=3_000.0).step_by(100.0));
-                    if (p.girder_height - prev).abs() > 1.0 { dirty = true; }
-
-                    let prev = p.slab_thickness;
-                    ui.label("슬래브 두께 (mm)");
-                    ui.add(egui::Slider::new(&mut p.slab_thickness, 150.0..=400.0).step_by(10.0));
-                    if (p.slab_thickness - prev).abs() > 1.0 { dirty = true; }
+                    param_slider!("경간 (m)",      &mut p.span_m,         20.0..=80.0,      1.0);
+                    param_slider!("거더 수",        &mut p.girder_count,   3..=7,            1.0);
+                    param_slider!("c/c 간격 (mm)", &mut p.girder_spacing, 1_500.0..=4_000.0, 100.0);
+                    param_slider!("거더 높이 (mm)",&mut p.girder_height,  1_000.0..=3_000.0, 100.0);
+                    param_slider!("슬래브 두께(mm)",&mut p.slab_thickness, 150.0..=400.0,    10.0);
 
                     ui.separator();
-                    if dirty {
-                        apply = ui.button("▶ 적용").clicked();
-                    } else {
+                    if dirty && !apply {
+                        // Manual apply button as fallback
+                        if ui.button("▶ 적용 (Apply)").clicked() { apply = true; }
+                        ui.small("* 슬라이더를 놓으면 자동 적용");
+                    } else if !dirty {
                         ui.label("✓ 최신 상태");
                     }