feat(galaxy): multi-disk galaxy generation with tab-based UI

- Add multi-disk support (up to 4 independent disk layers) with per-disk
  arms, twist, tilt, rotation, inner/outer radius
- Add polar beams (top/bottom) with taper, gravity, thickness controls
- Implement tab-based disk selector UI with add/remove disk
- Add Randomize Settings button for full param randomization
- Add Regenerate (reseed) and Center View buttons
- Add per-system contents generation (planets, belts, stations, anomalies,
  gas clouds, stargates) with orbital mechanics
- Refactor control panel into scrollable sections with value display

apps/game/src/gameplay/galaxy/mod.rs

@@ -45,6 +45,7 @@ impl Plugin for GalaxyPlugin {
                 Update,
                 (
                     escape_to_main_menu,
+                    ui::rebuild_scroll_content,
                     ui::param_button_handler,
                     ui::refresh_control_panel_values,
                     ui::scroll_control_panel,
@@ -181,21 +182,22 @@ fn generate_galaxy(
     (systems, contents, connections)
 }
 
-/// Position-only galaxy generation. Composes three structural layers —
-/// a [`CoreParams`] cluster, a [`DiskParams`] of horizontal spiral arms,
-/// and two [`BeamParams`] columns along ±Y — into a single flat list of
-/// systems ready for the connection graph and the spawner.
+/// Position-only galaxy generation. Composes multiple structural layers —
+/// a [`CoreParams`] cluster, up to [`MAX_DISKS`] independent [`DiskParams`]
+/// spiral disks, and two [`BeamParams`] columns along ±Y — into a single
+/// flat list of systems ready for the connection graph and the spawner.
 ///
 /// Each layer owns its own system count; the total galaxy population is
-/// `core.count + disk.count + beam_top.count + beam_bottom.count`. System
-/// indices are global across all layers (used for `g-{n}` IDs and name
-/// suffixes) so the connection graph and POI generator see one consistent
-/// vector.
+/// `core.count + Σ disks[].count + beam_top.count + beam_bottom.count`.
+/// System indices are global across all layers (used for `g-{n}` IDs and
+/// name suffixes) so the connection graph and POI generator see one
+/// consistent vector.
 fn generate_system_positions(params: &GalaxyParams, rng: &mut StdRng) -> Vec<GeneratedSystem> {
     // Total budget — pre-allocation only; each pass appends as many systems
     // as it manages to place.
+    let disk_total: usize = params.disks.iter().map(|d| d.count).sum();
     let total = params.core.count
-        + params.disk.count
+        + disk_total
         + params.beam_top.count
         + params.beam_bottom.count;
     let mut systems: Vec<GeneratedSystem> = Vec::with_capacity(total);
@@ -209,14 +211,19 @@ fn generate_system_positions(params: &GalaxyParams, rng: &mut StdRng) -> Vec<Gen
     let mut next_index = 0usize;
 
     generate_core(&mut systems, rng, &params.core, params.size, base_spacing, &mut next_index);
-    generate_disk(
-        &mut systems,
-        rng,
-        &params.disk,
-        params.size,
-        base_spacing,
-        &mut next_index,
-    );
+
+    for (disk_index, disk) in params.disks.iter().enumerate() {
+        generate_disk(
+            &mut systems,
+            rng,
+            disk,
+            params.size,
+            base_spacing,
+            &mut next_index,
+            disk_index,
+        );
+    }
+
     if params.beam_top.enabled {
         generate_beam(
             &mut systems,
@@ -302,9 +309,10 @@ fn generate_core(
     }
 }
 
-/// Generate the horizontal disk of spiral arms in the XZ plane. Faithful to
-/// the original generator's density bias (`pow(0.62)` → packed near origin)
-/// and arm twist.
+/// Generate one disk layer of spiral arms. Faithful to the original
+/// generator's density bias (`pow(0.62)` → packed near origin) and arm twist.
+/// Supports tilt (rotation around X, capped at 45°), Y-axis rotation offset,
+/// and independent inner/outer radii.
 fn generate_disk(
     systems: &mut Vec<GeneratedSystem>,
     rng: &mut StdRng,
@@ -312,24 +320,53 @@ fn generate_disk(
     galaxy_size: f32,
     base_spacing: f32,
     next_index: &mut usize,
+    disk_index: usize,
 ) {
     let arm_count = disk.arms.max(1);
+    // Effective outer radius: explicit value if set, else galaxy size.
+    let outer = if disk.outer_radius > 0.0 {
+        disk.outer_radius
+    } else {
+        galaxy_size
+    };
+    let inner = disk.inner_radius;
+    let span = (outer - inner).max(1.0);
+
+    // Pre-compute the rotation quaternion for this disk's tilt + Y rotation.
+    // Tilt is applied first (around X), then the Y rotation offset.
+    let disk_rotation = if disk.tilt.abs() > 0.001 || disk.rotation_offset.abs() > 0.001 {
+        let tilt = Quat::from_rotation_x(disk.tilt);
+        let yaw = Quat::from_rotation_y(disk.rotation_offset);
+        Some(yaw * tilt)
+    } else {
+        None
+    };
+
     for i in 0..disk.count {
         let arm = (i as u32) % arm_count;
         // Non-core disk factions cycle through Amarr/Minmatar/Gallente/Caldari.
-        let faction_index = 1 + (arm as usize) % (FACTIONS.len() - 1);
+        // Offset by disk_index so different disks don't all share the same
+        // faction assignment pattern.
+        let faction_index =
+            1 + ((arm as usize + disk_index) % (FACTIONS.len() - 1));
         let (faction, color) = FACTIONS[faction_index];
 
         let mut position = Option::<Vec3>::None;
         let mut final_radius = 0.0f32;
         for attempt in 0..SPACING_ATTEMPTS {
-            let r = rng.gen::<f32>().powf(0.62) * galaxy_size;
+            let r = inner + rng.gen::<f32>().powf(0.62) * span;
             let angle = std::f32::consts::TAU * arm as f32 / arm_count as f32
-                + (r / galaxy_size) * disk.twist
+                + ((r - inner) / span) * disk.twist
                 + (rng.gen::<f32>() - 0.5) * 0.72;
             let y = (rng.gen::<f32>() - 0.5) * 20.0;
-            let candidate = Vec3::new(angle.cos() * r, y, angle.sin() * r);
-            final_radius = r;
+            let mut candidate = Vec3::new(angle.cos() * r, y, angle.sin() * r);
+
+            // Apply tilt + rotation for non-flat disks.
+            if let Some(rot) = disk_rotation {
+                candidate = rot * candidate;
+            }
+
+            final_radius = candidate.length();
             let spacing = relax_spacing(base_spacing, attempt).max(MIN_SYSTEM_SPACING);
             if systems
                 .iter()
@@ -356,7 +393,10 @@ fn generate_disk(
             color,
             security,
             is_core: false,
-            origin: SystemOrigin::Disk { arm },
+            origin: SystemOrigin::Disk {
+                disk: disk_index,
+                arm,
+            },
         });
     }
 }
@@ -478,7 +518,12 @@ fn security_for_radius(radius: f32, galaxy_size: f32) -> f32 {
 #[derive(Debug, Clone, Copy)]
 enum SystemOrigin {
     Core,
-    Disk { arm: u32 },
+    Disk {
+        /// Which disk layer this system belongs to (index into [`GalaxyParams::disks`]).
+        disk: usize,
+        /// Which arm within the disk.
+        arm: u32,
+    },
     Beam { side: BeamTag },
 }
 

apps/game/src/gameplay/galaxy/params.rs

@@ -6,9 +6,10 @@
 //!
 //! ## Structure
 //!
-//! A galaxy is composed of three layers, each owning its own system count:
+//! A galaxy is composed of three structural layer types:
 //! - [`CoreParams`] — Concord systems clustered near the origin.
-//! - [`DiskParams`] — horizontal spiral arms in the XZ plane.
+//! - [`DiskParams`] (up to [`MAX_DISKS`]) — independent spiral disks, each
+//!   with its own arm count, twist, tilt, rotation, and radial extent.
 //! - [`BeamParams`] (×2, top and bottom) — vertical columns of systems along
 //!   ±Y, the "polar beams". Each beam is its own population of selectable
 //!   star systems, fully equal citizens to disk arms.
@@ -57,6 +58,9 @@ pub const CORE_RADIUS_MIN: f32 = 10.0;
 pub const CORE_RADIUS_MAX: f32 = 120.0;
 pub const CORE_RADIUS_STEP: f32 = 5.0;
 
+/// Maximum number of independent disk layers.
+pub const MAX_DISKS: usize = 4;
+
 pub const DISK_COUNT_MIN: usize = 20;
 pub const DISK_COUNT_MAX: usize = 220;
 pub const DISK_COUNT_STEP: usize = 4;
@@ -66,6 +70,24 @@ pub const DISK_TWIST_MIN: f32 = 1.0;
 pub const DISK_TWIST_MAX: f32 = 6.0;
 pub const DISK_TWIST_STEP: f32 = 0.2;
 
+/// Max tilt is 45° — disks should never be parallel to beams.
+pub const DISK_TILT_MIN: f32 = 0.0;
+pub const DISK_TILT_MAX: f32 = std::f32::consts::FRAC_PI_4;
+/// ~5° steps (45° / 9).
+pub const DISK_TILT_STEP: f32 = std::f32::consts::FRAC_PI_4 / 9.0;
+
+pub const DISK_ROTATION_MIN: f32 = 0.0;
+pub const DISK_ROTATION_MAX: f32 = std::f32::consts::TAU;
+/// 30° steps.
+pub const DISK_ROTATION_STEP: f32 = std::f32::consts::TAU / 12.0;
+
+pub const DISK_INNER_RADIUS_MIN: f32 = 0.0;
+pub const DISK_INNER_RADIUS_MAX: f32 = 400.0;
+pub const DISK_INNER_RADIUS_STEP: f32 = 10.0;
+pub const DISK_OUTER_RADIUS_MIN: f32 = 40.0;
+pub const DISK_OUTER_RADIUS_MAX: f32 = 420.0;
+pub const DISK_OUTER_RADIUS_STEP: f32 = 10.0;
+
 pub const BEAM_COUNT_MIN: usize = 0;
 pub const BEAM_COUNT_MAX: usize = 120;
 pub const BEAM_COUNT_STEP: usize = 4;
@@ -115,12 +137,31 @@ impl Default for CoreParams {
     }
 }
 
-/// Horizontal disk of spiral arms in the XZ plane.
+/// One independent disk layer of spiral arms.
+///
+/// Disks are generated in the XZ plane and then tilted by [`Self::tilt`]
+/// (rotation around the X axis) and rotated by [`Self::rotation_offset`]
+/// (around the Y axis). Systems are placed between [`Self::inner_radius`]
+/// and [`Self::outer_radius`]; if `outer_radius` is 0 the galaxy-wide
+/// [`GalaxyParams::size`] is used instead.
 #[derive(Debug, Clone)]
 pub struct DiskParams {
     pub count: usize,
     pub arms: u32,
     pub twist: f32,
+    /// Tilt angle in radians (rotation around X axis).
+    /// Capped at 45° so disks never become parallel to beams.
+    /// 0 = flat in XZ plane, π/4 = maximum tilt.
+    pub tilt: f32,
+    /// Rotation offset around Y axis in radians.
+    /// Rotates the disk in the horizontal plane, determining where the
+    /// tilted disk's "high side" points.
+    pub rotation_offset: f32,
+    /// Minimum distance from the origin for systems in this disk.
+    /// 0 = systems can start at the origin (overlapping the core).
+    pub inner_radius: f32,
+    /// Maximum distance from the origin. 0 = use [`GalaxyParams::size`].
+    pub outer_radius: f32,
 }
 
 impl Default for DiskParams {
@@ -129,6 +170,10 @@ impl Default for DiskParams {
             count: DEFAULT_DISK_COUNT,
             arms: DEFAULT_DISK_ARMS,
             twist: DEFAULT_DISK_TWIST,
+            tilt: 0.0,
+            rotation_offset: 0.0,
+            inner_radius: 0.0,
+            outer_radius: 0.0, // means "use galaxy size"
         }
     }
 }
@@ -189,7 +234,8 @@ pub struct GalaxyParams {
     /// Overall galaxy extent — drives the disk radius.
     pub size: f32,
     pub core: CoreParams,
-    pub disk: DiskParams,
+    /// Independent disk layers. Always contains at least one entry.
+    pub disks: Vec<DiskParams>,
     pub beam_top: BeamParams,
     pub beam_bottom: BeamParams,
     /// Monotonic counter — any mutation must bump this via [`Self::bump_generation`].
@@ -204,7 +250,7 @@ impl Default for GalaxyParams {
             seed: DEFAULT_SEED,
             size: DEFAULT_SIZE,
             core: CoreParams::default(),
-            disk: DiskParams::default(),
+            disks: vec![DiskParams::default()],
             beam_top: BeamParams::default(),
             beam_bottom: BeamParams::default(),
             generation: 0,