diff --git a/src/ui/mod.rs b/src/ui/mod.rs
index 3cfd6b6..16e6174 100644
--- a/src/ui/mod.rs
+++ b/src/ui/mod.rs
@@ -1,3 +1,4 @@
+mod sections;
 mod style;
 pub mod preset;
 
diff --git a/src/ui/sections.rs b/src/ui/sections.rs
new file mode 100644
index 0000000..3b1f153
--- /dev/null
+++ b/src/ui/sections.rs
@@ -0,0 +1,119 @@
+//! Per-group section render functions. Each takes the `&mut egui::Ui` it
+//! draws into plus the params/camera refs it needs. The `ui_system`
+//! orchestrator (mod.rs) calls them inside `group()` / `collapsing()`.
+
+use bevy_egui::egui;
+
+use crate::camera::OrbitCamera;
+use crate::params::{
+    AaQuality, BlackHoleParams, BloomQuality,
+};
+use crate::ui::style::MUTED_TEXT;
+
+use std::f32::consts::PI;
+
+/// Shared two-column row helper: label + sized widget.
+fn row(
+    ui: &mut egui::Ui,
+    label: &str,
+    add_widget: impl FnOnce(&mut egui::Ui) -> egui::Response,
+) {
+    ui.label(label);
+    add_widget(ui);
+    ui.end_row();
+}
+
+// ============================ Always-open cards ============================
+
+pub fn section_camera(ui: &mut egui::Ui, cam: &mut OrbitCamera) {
+    egui::Grid::new("camera_grid").num_columns(2).spacing([8.0, 4.0])
+        .show(ui, |ui| {
+            row(ui, "Distance", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut cam.distance, 3.0..=200.0)
+                    .suffix(" r_g").fixed_decimals(1)));
+            row(ui, "Yaw", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut cam.yaw, -PI..=PI)
+                    .suffix(" rad").fixed_decimals(2)));
+            row(ui, "Pitch", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut cam.pitch, (-PI + 0.05)..=(PI - 0.05))
+                    .suffix(" rad").fixed_decimals(2)));
+            row(ui, "FOV", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut cam.fov, 0.3..=2.0).fixed_decimals(2)));
+        });
+}
+
+pub fn section_black_hole(ui: &mut egui::Ui, params: &mut BlackHoleParams) {
+    egui::Grid::new("bh_grid").num_columns(2).spacing([8.0, 4.0])
+        .show(ui, |ui| {
+            row(ui, "Spin (χ)", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut params.spin, 0.0..=1.0).fixed_decimals(2)));
+            // Read-only derived values: right column, muted color.
+            ui.label(egui::RichText::new("ISCO (disk inner)").color(MUTED_TEXT));
+            ui.label(egui::RichText::new(format!("{:.3}", crate::physics::kerr_isco(params.spin)))
+                .color(MUTED_TEXT));
+            ui.end_row();
+            ui.label(egui::RichText::new("Horizon r+").color(MUTED_TEXT));
+            ui.label(egui::RichText::new(format!("{:.3}", crate::physics::kerr_horizon(params.spin)))
+                .color(MUTED_TEXT));
+            ui.end_row();
+        });
+}
+
+pub fn section_quality(ui: &mut egui::Ui, params: &mut BlackHoleParams) {
+    // Bloom quality combobox + threshold/strength (hidden when Off — §4.3).
+    {
+        let mut q = params.bloom_quality;
+        egui::Grid::new("bloom_grid").num_columns(2).spacing([8.0, 4.0])
+            .show(ui, |ui| {
+                ui.label("Bloom");
+                egui::ComboBox::from_id_salt("bloom_combo")
+                    .selected_text(format!("{:?}", q))
+                    .show_ui(ui, |ui| {
+                        ui.selectable_value(&mut q, BloomQuality::Off, "Off");
+                        ui.selectable_value(&mut q, BloomQuality::Low, "Low");
+                        ui.selectable_value(&mut q, BloomQuality::Medium, "Medium");
+                        ui.selectable_value(&mut q, BloomQuality::High, "High");
+                    });
+                ui.end_row();
+            });
+        params.bloom_quality = q;
+    }
+    if params.bloom_quality != BloomQuality::Off {
+        egui::Grid::new("bloom_detail_grid").num_columns(2).spacing([8.0, 4.0])
+            .show(ui, |ui| {
+                row(ui, "Threshold", |ui| ui.add_sized([140.0, 16.0],
+                    egui::Slider::new(&mut params.bloom_threshold, 0.0..=3.0).fixed_decimals(2)));
+                row(ui, "Strength", |ui| ui.add_sized([140.0, 16.0],
+                    egui::Slider::new(&mut params.bloom_strength, 0.0..=2.0).fixed_decimals(2)));
+            });
+    }
+    egui::Grid::new("renderer_grid").num_columns(2).spacing([8.0, 4.0])
+        .show(ui, |ui| {
+            // steps + render_scale migrated here from the deleted Renderer section.
+            row(ui, "Steps", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut params.steps, 50..=600)
+                    .logarithmic(true).fixed_decimals(0)));
+            row(ui, "Resolution", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut params.render_scale, 0.25..=1.0)
+                    .logarithmic(true).fixed_decimals(2)));
+            row(ui, "Exposure", |ui| ui.add_sized([140.0, 16.0],
+                egui::Slider::new(&mut params.exposure, 0.5..=3.0).fixed_decimals(2)));
+            row(ui, "Star AA", |ui| ui.checkbox(&mut params.star_aa, ""));
+            // Ring anti-alias (supersampling for lensed-image rings).
+            let mut a = params.aa_quality;
+            ui.label("Ring AA");
+            egui::ComboBox::from_id_salt("aa_combo")
+                .selected_text(format!("{:?} ({}×)", a, a.samples()))
+                .show_ui(ui, |ui| {
+                    ui.selectable_value(&mut a, AaQuality::Off, "Off (1×)");
+                    ui.selectable_value(&mut a, AaQuality::Low, "Low (2×)");
+                    ui.selectable_value(&mut a, AaQuality::High, "High (4×)");
+                });
+            ui.end_row();
+            params.aa_quality = a;
+        });
+    ui.label(
+        egui::RichText::new("MSAA is decorative on a fullscreen shader (no geometry edges).")
+            .small().color(MUTED_TEXT),
+    );
+}