diff --git a/crates/voltex_renderer/src/blas_update.rs b/crates/voltex_renderer/src/blas_update.rs
new file mode 100644
index 0000000..189bc75
--- /dev/null
+++ b/crates/voltex_renderer/src/blas_update.rs
@@ -0,0 +1,34 @@
+/// Tracks which meshes need BLAS rebuild.
+pub struct BlasTracker {
+    dirty: Vec<(u32, bool)>, // (mesh_id, needs_rebuild)
+}
+
+impl BlasTracker {
+    pub fn new() -> Self { BlasTracker { dirty: Vec::new() } }
+    pub fn register(&mut self, mesh_id: u32) { self.dirty.push((mesh_id, false)); }
+    pub fn mark_dirty(&mut self, mesh_id: u32) {
+        if let Some(entry) = self.dirty.iter_mut().find(|(id, _)| *id == mesh_id) { entry.1 = true; }
+    }
+    pub fn dirty_meshes(&self) -> Vec<u32> { self.dirty.iter().filter(|(_, d)| *d).map(|(id, _)| *id).collect() }
+    pub fn clear_dirty(&mut self) { for entry in &mut self.dirty { entry.1 = false; } }
+    pub fn mesh_count(&self) -> usize { self.dirty.len() }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_register_and_dirty() {
+        let mut t = BlasTracker::new();
+        t.register(1); t.register(2);
+        t.mark_dirty(1);
+        assert_eq!(t.dirty_meshes(), vec![1]);
+    }
+    #[test]
+    fn test_clear_dirty() {
+        let mut t = BlasTracker::new();
+        t.register(1); t.mark_dirty(1);
+        t.clear_dirty();
+        assert!(t.dirty_meshes().is_empty());
+    }
+}
diff --git a/crates/voltex_renderer/src/lib.rs b/crates/voltex_renderer/src/lib.rs
index dd2d452..19df023 100644
--- a/crates/voltex_renderer/src/lib.rs
+++ b/crates/voltex_renderer/src/lib.rs
@@ -100,3 +100,12 @@ pub mod bilateral_bloom;
 pub use png::parse_png;
 pub use jpg::parse_jpg;
 pub use gltf::{parse_gltf, GltfData, GltfMesh, GltfMaterial};
+pub mod soft_rt_shadow;
+pub mod blas_update;
+pub use blas_update::BlasTracker;
+pub mod rt_fallback;
+pub use rt_fallback::{RtCapabilities, RenderMode};
+pub mod light_probes;
+pub use light_probes::{LightProbe, LightProbeGrid};
+pub mod light_volumes;
+pub use light_volumes::LightVolume;
diff --git a/crates/voltex_renderer/src/light_probes.rs b/crates/voltex_renderer/src/light_probes.rs
new file mode 100644
index 0000000..193a376
--- /dev/null
+++ b/crates/voltex_renderer/src/light_probes.rs
@@ -0,0 +1,63 @@
+pub struct LightProbe {
+    pub position: [f32; 3],
+    pub sh_coefficients: [[f32; 3]; 9], // L2 SH, 9 RGB coefficients
+}
+
+impl LightProbe {
+    pub fn new(position: [f32; 3]) -> Self {
+        LightProbe { position, sh_coefficients: [[0.0; 3]; 9] }
+    }
+    pub fn evaluate_irradiance(&self, normal: [f32; 3]) -> [f32; 3] {
+        // L0
+        let mut result = [self.sh_coefficients[0][0], self.sh_coefficients[0][1], self.sh_coefficients[0][2]];
+        // L1
+        let (nx, ny, nz) = (normal[0], normal[1], normal[2]);
+        for c in 0..3 {
+            result[c] += self.sh_coefficients[1][c] * ny;
+            result[c] += self.sh_coefficients[2][c] * nz;
+            result[c] += self.sh_coefficients[3][c] * nx;
+        }
+        result
+    }
+}
+
+pub struct LightProbeGrid {
+    probes: Vec<LightProbe>,
+}
+
+impl LightProbeGrid {
+    pub fn new() -> Self { LightProbeGrid { probes: Vec::new() } }
+    pub fn add(&mut self, probe: LightProbe) { self.probes.push(probe); }
+    pub fn nearest(&self, pos: [f32; 3]) -> Option<&LightProbe> {
+        self.probes.iter().min_by(|a, b| {
+            let da = dist_sq(a.position, pos);
+            let db = dist_sq(b.position, pos);
+            da.partial_cmp(&db).unwrap()
+        })
+    }
+    pub fn len(&self) -> usize { self.probes.len() }
+}
+
+fn dist_sq(a: [f32; 3], b: [f32; 3]) -> f32 {
+    let dx = a[0]-b[0]; let dy = a[1]-b[1]; let dz = a[2]-b[2]; dx*dx+dy*dy+dz*dz
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_probe_evaluate() {
+        let mut p = LightProbe::new([0.0; 3]);
+        p.sh_coefficients[0] = [0.5, 0.5, 0.5]; // ambient
+        let irr = p.evaluate_irradiance([0.0, 1.0, 0.0]);
+        assert!(irr[0] > 0.0);
+    }
+    #[test]
+    fn test_grid_nearest() {
+        let mut grid = LightProbeGrid::new();
+        grid.add(LightProbe::new([0.0, 0.0, 0.0]));
+        grid.add(LightProbe::new([10.0, 0.0, 0.0]));
+        let nearest = grid.nearest([1.0, 0.0, 0.0]).unwrap();
+        assert!((nearest.position[0] - 0.0).abs() < 1e-6);
+    }
+}
diff --git a/crates/voltex_renderer/src/light_volumes.rs b/crates/voltex_renderer/src/light_volumes.rs
new file mode 100644
index 0000000..9f351ff
--- /dev/null
+++ b/crates/voltex_renderer/src/light_volumes.rs
@@ -0,0 +1,54 @@
+/// Light volume shapes for deferred lighting optimization.
+#[derive(Debug, Clone)]
+pub enum LightVolume {
+    Sphere { center: [f32; 3], radius: f32 },
+    Cone { apex: [f32; 3], direction: [f32; 3], angle: f32, range: f32 },
+    Fullscreen,
+}
+
+impl LightVolume {
+    pub fn point_light(center: [f32; 3], radius: f32) -> Self { LightVolume::Sphere { center, radius } }
+    pub fn spot_light(apex: [f32; 3], dir: [f32; 3], angle: f32, range: f32) -> Self {
+        LightVolume::Cone { apex, direction: dir, angle, range }
+    }
+    pub fn directional() -> Self { LightVolume::Fullscreen }
+
+    pub fn contains_point(&self, point: [f32; 3]) -> bool {
+        match self {
+            LightVolume::Sphere { center, radius } => {
+                let dx = point[0]-center[0]; let dy = point[1]-center[1]; let dz = point[2]-center[2];
+                dx*dx + dy*dy + dz*dz <= radius * radius
+            }
+            LightVolume::Fullscreen => true,
+            LightVolume::Cone { apex, direction, angle, range } => {
+                let dx = point[0]-apex[0]; let dy = point[1]-apex[1]; let dz = point[2]-apex[2];
+                let dist = (dx*dx+dy*dy+dz*dz).sqrt();
+                if dist > *range { return false; }
+                if dist < 1e-6 { return true; }
+                let dot = (dx*direction[0]+dy*direction[1]+dz*direction[2]) / dist;
+                dot >= angle.cos()
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_sphere_contains() {
+        let v = LightVolume::point_light([0.0; 3], 5.0);
+        assert!(v.contains_point([3.0, 0.0, 0.0]));
+        assert!(!v.contains_point([6.0, 0.0, 0.0]));
+    }
+    #[test]
+    fn test_fullscreen() {
+        assert!(LightVolume::directional().contains_point([999.0, 999.0, 999.0]));
+    }
+    #[test]
+    fn test_cone_contains() {
+        let v = LightVolume::spot_light([0.0;3], [0.0,0.0,-1.0], 0.5, 10.0);
+        assert!(v.contains_point([0.0, 0.0, -5.0])); // on axis
+        assert!(!v.contains_point([0.0, 0.0, 5.0])); // behind
+    }
+}
diff --git a/crates/voltex_renderer/src/rt_fallback.rs b/crates/voltex_renderer/src/rt_fallback.rs
new file mode 100644
index 0000000..7961940
--- /dev/null
+++ b/crates/voltex_renderer/src/rt_fallback.rs
@@ -0,0 +1,57 @@
+/// Check if a wgpu adapter supports features needed for RT.
+pub struct RtCapabilities {
+    pub supports_compute: bool,
+    pub supports_storage_textures: bool,
+    pub supports_timestamp_query: bool,
+}
+
+impl RtCapabilities {
+    /// Evaluate capabilities (simplified — real check would use adapter.features()).
+    pub fn evaluate(max_storage_buffers: u32, max_compute_workgroup_size: u32) -> Self {
+        RtCapabilities {
+            supports_compute: max_compute_workgroup_size >= 256,
+            supports_storage_textures: max_storage_buffers >= 4,
+            supports_timestamp_query: false, // opt-in feature
+        }
+    }
+
+    pub fn can_use_rt(&self) -> bool { self.supports_compute && self.supports_storage_textures }
+}
+
+/// Fallback rendering mode when RT is not available.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum RenderMode {
+    Full,           // All RT features
+    NoRtShadows,    // Use shadow maps instead
+    NoRtReflections,// Use SSR instead
+    Minimal,        // Shadow maps + no reflections
+}
+
+pub fn select_render_mode(caps: &RtCapabilities) -> RenderMode {
+    if caps.can_use_rt() { RenderMode::Full }
+    else if caps.supports_compute { RenderMode::NoRtShadows }
+    else { RenderMode::Minimal }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_full_caps() {
+        let c = RtCapabilities::evaluate(8, 256);
+        assert!(c.can_use_rt());
+        assert_eq!(select_render_mode(&c), RenderMode::Full);
+    }
+    #[test]
+    fn test_no_compute() {
+        let c = RtCapabilities::evaluate(8, 64);
+        assert!(!c.can_use_rt());
+        assert_eq!(select_render_mode(&c), RenderMode::Minimal);
+    }
+    #[test]
+    fn test_limited_storage() {
+        let c = RtCapabilities::evaluate(2, 256);
+        assert!(!c.can_use_rt());
+        assert_eq!(select_render_mode(&c), RenderMode::NoRtShadows);
+    }
+}
diff --git a/crates/voltex_renderer/src/soft_rt_shadow.rs b/crates/voltex_renderer/src/soft_rt_shadow.rs
new file mode 100644
index 0000000..f390d68
--- /dev/null
+++ b/crates/voltex_renderer/src/soft_rt_shadow.rs
@@ -0,0 +1,34 @@
+use bytemuck::{Pod, Zeroable};
+
+#[repr(C)]
+#[derive(Copy, Clone, Pod, Zeroable)]
+pub struct SoftShadowParams {
+    pub light_dir: [f32; 3],
+    pub num_rays: u32,
+    pub light_radius: f32,
+    pub max_distance: f32,
+    pub _pad: [f32; 2],
+}
+
+impl SoftShadowParams {
+    pub fn new() -> Self {
+        SoftShadowParams { light_dir: [0.0, -1.0, 0.0], num_rays: 16, light_radius: 0.02, max_distance: 50.0, _pad: [0.0; 2] }
+    }
+}
+
+/// Penumbra estimation: wider penumbra for objects farther from occluder.
+pub fn penumbra_size(light_radius: f32, blocker_dist: f32, receiver_dist: f32) -> f32 {
+    if blocker_dist < 1e-6 { return 0.0; }
+    light_radius * (receiver_dist - blocker_dist) / blocker_dist
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_params_default() { let p = SoftShadowParams::new(); assert_eq!(p.num_rays, 16); }
+    #[test]
+    fn test_penumbra_close() { assert!((penumbra_size(0.02, 1.0, 1.1) - 0.002).abs() < 0.001); }
+    #[test]
+    fn test_penumbra_far() { assert!(penumbra_size(0.02, 1.0, 5.0) > penumbra_size(0.02, 1.0, 2.0)); }
+}