intersection returns distance along ray

src/ds/aabb.rs

@@ -47,7 +47,7 @@ impl Aabb {
 }
 
 impl Renderable for Aabb {
-    fn intersects(&self, ray: &ds::Ray) -> bool {
+    fn intersects(&self, ray: &ds::Ray) -> Option<f64> {
         let axes = [ // each slab we check
             (&self.x, ray.origin.x, ray.direction.x),
             (&self.y, ray.origin.y, ray.direction.y),
@@ -61,7 +61,7 @@ impl Renderable for Aabb {
             if dir.abs() < f64::EPSILON {
                 // Ray is parallel to this slab — check if origin is inside it
                 if origin < interval.min() || origin > interval.max() {
-                    return false;
+                    return None;
                 }
                 continue;
             }
@@ -76,10 +76,10 @@ impl Renderable for Aabb {
             t_exit  = t_exit.min(t_far);
 
             if t_enter > t_exit {
-                return false;
+                return None;
             }
         }
-        return true
+        return Some(t_enter);
     }
 
     fn as_any(&self) -> &dyn std::any::Any {

src/object/quad.rs

@@ -55,16 +55,16 @@ impl Renderable for Quad {
         self.q + self.u/2.0 + self.v/2.0
     }
 
-    fn intersects(&self, ray: &ds::Ray) -> bool {
+    fn intersects(&self, ray: &ds::Ray) -> Option<f64> {
         let denominator = self.normal.dot(&ray.direction);
 
         if denominator.abs() < 0.00000001 {
-            return false;
+            return None;
         }
 
         let t = (self.d - self.normal.dot(&ray.origin)) / denominator;
 
-        if t < 0.0 { return false; }
+        if t < 0.0 { return None; }
 
         let intersection = ray.at(t);
         let planar_hit = intersection - self.q;
@@ -76,10 +76,10 @@ impl Renderable for Quad {
         let beta =  self.v.dot(&planar_hit) / v_len_sq;
 
         if alpha < 0.0 || alpha > 1.0 || beta < 0.0 || beta > 1.0 {
-            return false;
+            return None;
         }
 
-        return true
+        return Some(t)
     }
 }
 

src/object/renderable.rs

@@ -1,7 +1,7 @@
 pub trait Renderable: Send + Sync {
     fn as_any(&self) -> &dyn std::any::Any;
     fn center(&self) -> crate::ds::Vector3;
-    fn intersects(&self, ray: &crate::ds::Ray) -> bool;
+    fn intersects(&self, ray: &crate::ds::Ray) -> Option<f64>;
 }
 
 pub trait ToGpu<T> {

src/object/sphere.rs

@@ -43,21 +43,24 @@ impl Renderable for Sphere {
         self.center
     }
 
-    fn intersects(&self, ray: &ds::Ray) -> bool {
+    fn intersects(&self, ray: &ds::Ray) -> Option<f64> {
         let oc = self.center - ray.origin;
         let a  = ray.direction.dot(&ray.direction);
         let h  = ray.direction.dot(&oc);
         let c  = oc.dot(&oc) - self.radius * self.radius;
         let discriminant = h*h - a*c;
 
         if discriminant < 0.0 {
-            return false;
+            return None;
         }
 
         let t1 = (h - discriminant.sqrt()) / a;
         let t2 = (h + discriminant.sqrt()) / a;
 
-        return t1 > 1e-8 || t2 > 1e-8
+        if t1 > 1e-8 { return Some(t1) }
+        if t2 > 1e-8 { return Some(t2) }
+
+        return None
     }
 }