feat: Implement hybrid rendering with SDF primitives

- Added SDF logic for Sphere, Box, and Torus in WGSL.
- Implemented hybrid normal calculation (analytical for sphere, numerical fallback).
- Updated Renderer3D to dispatch object types to shader.
- Updated test_3d_render to display mixed SDF shapes (Sphere, Torus, Box).
- Added BOX to ObjectType enum.

3 files changed, 150 insertions, 30 deletions

diff --git a/src/3d/object.h b/src/3d/object.h
index f4215aa..ccbb1e1 100644
--- a/src/3d/object.h
+++ b/src/3d/object.h
@@ -10,7 +10,8 @@ enum class ObjectType {
   CUBE,
   SPHERE,
   PLANE,
-  TORUS
+  TORUS,
+  BOX
   // Add more SDF types here
 };
 
diff --git a/src/3d/renderer.cc b/src/3d/renderer.cc
index 1745a97..2e08b4e 100644
--- a/src/3d/renderer.cc
+++ b/src/3d/renderer.cc
@@ -76,19 +76,14 @@ struct VertexOutput {
     @builtin(position) position: vec4<f32>,
     @location(0) local_pos: vec3<f32>,
     @location(1) color: vec4<f32>,
+    @location(2) @interpolate(flat) instance_index: u32,
+    @location(3) world_pos: vec3<f32>,
 };
 
 @vertex
 fn vs_main(@builtin(vertex_index) vertex_index: u32, 
            @builtin(instance_index) instance_index: u32) -> VertexOutput {
     
-    // Hardcoded cube vertices (similar to C++ array but in shader for simplicity if desired, 
-    // but here we might assume a vertex buffer or just generate logic. 
-    // For this demo, let's use the buffer-less approach for vertices if we want to save space, 
-    // but we have a C++ array. Let's just generate a cube on the fly from index?)
-    // Actually, let's map the C++ kCubeVertices to a vertex buffer or use a hardcoded array here.
-    // For 64k size, hardcoded in shader is good.
-    
     var pos = array<vec3<f32>, 36>(
         vec3(-1.0, -1.0,  1.0), vec3( 1.0, -1.0,  1.0), vec3( 1.0,  1.0,  1.0),
         vec3(-1.0, -1.0,  1.0), vec3( 1.0,  1.0,  1.0), vec3(-1.0,  1.0,  1.0),
@@ -113,31 +108,140 @@ fn vs_main(@builtin(vertex_index) vertex_index: u32,
 
     var out: VertexOutput;
     out.position = clip_pos;
-    out.local_pos = p;
+    out.local_pos = p; // Proxy geometry local coords (-1 to 1)
     out.color = obj.color;
+    out.instance_index = instance_index;
+    out.world_pos = world_pos.xyz;
     return out;
 }
 
+// --- SDF Primitives ---
+// All primitives are centered at 0,0,0
+
+fn sdSphere(p: vec3<f32>, r: f32) -> f32 {
+    return length(p) - r;
+}
+
+fn sdBox(p: vec3<f32>, b: vec3<f32>) -> f32 {
+    let q = abs(p) - b;
+    return length(max(q, vec3<f32>(0.0))) + min(max(q.x, max(q.y, q.z)), 0.0);
+}
+
+fn sdTorus(p: vec3<f32>, t: vec2<f32>) -> f32 {
+    let q = vec2<f32>(length(p.xz) - t.x, p.y);
+    return length(q) - t.y;
+}
+
+// --- Dispatchers ---
+
+// Type IDs: 0=Cube(Wireframe proxy), 1=Sphere, 2=Box, 3=Torus
+fn get_dist(p: vec3<f32>, type: f32) -> f32 {
+    if (type == 1.0) { return sdSphere(p, 0.9); }
+    if (type == 2.0) { return sdBox(p, vec3<f32>(0.7)); }
+    if (type == 3.0) { return sdTorus(p, vec2<f32>(0.6, 0.25)); }
+    return 100.0;
+}
+
+// Analytical normals where possible, fallback to Numerical
+fn get_normal(p: vec3<f32>, type: f32) -> vec3<f32> {
+    if (type == 1.0) { // Sphere
+        return normalize(p); // Center is 0,0,0
+    }
+    
+    // Finite Difference for others
+    let e = vec2<f32>(0.001, 0.0);
+    return normalize(vec3<f32>(
+        get_dist(p + e.xyy, type) - get_dist(p - e.xyy, type),
+        get_dist(p + e.yxy, type) - get_dist(p - e.yxy, type),
+        get_dist(p + e.yyx, type) - get_dist(p - e.yyx, type)
+    ));
+}
+
 @fragment
 fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
-    // Simple wireframe-ish effect using barycentric coords logic? 
-    // Or just check proximity to edge of local cube?
-    let d = abs(in.local_pos);
-    let edge_dist = max(max(d.x, d.y), d.z);
+    let obj = object_data.objects[in.instance_index];
+    let type = obj.params.x;
+
+    // Case 0: The central cube (Wireframe/Solid Box logic) - Proxy only
+    if (type == 0.0) {
+        let d = abs(in.local_pos);
+        let edge_dist = max(max(d.x, d.y), d.z);
+        
+        var col = in.color.rgb;
+        if (edge_dist > 0.95) {
+            col = vec3<f32>(1.0, 1.0, 1.0); // White edges
+        } else {
+             // Simple face shading
+            let normal = normalize(cross(dpdx(in.local_pos), dpdy(in.local_pos)));
+            let light = normalize(vec3<f32>(0.5, 1.0, 0.5));
+            let diff = max(dot(normal, light), 0.2);
+            col = col * diff;
+        }
+        return vec4<f32>(col, 1.0);
+    }
+    
+    // Case 1+: Raymarching inside the proxy box
+    let center = vec3<f32>(obj.model[3].x, obj.model[3].y, obj.model[3].z);
+    
+    // Scale: Assume uniform scale from model matrix
+    let scale = length(vec3<f32>(obj.model[0].x, obj.model[0].y, obj.model[0].z));
+    
+    let ro = globals.camera_pos;
+    let rd = normalize(in.world_pos - globals.camera_pos);
     
-    // Mix object color with edge highlight
-    var col = in.color.rgb;
-    if (edge_dist > 0.95) {
-        col = vec3<f32>(1.0, 1.0, 1.0); // White edges
-    } else {
-        // Simple shading
-        let normal = normalize(cross(dpdx(in.local_pos), dpdy(in.local_pos)));
-        let light = normalize(vec3<f32>(0.5, 1.0, 0.5));
-        let diff = max(dot(normal, light), 0.2);
-        col = col * diff;
+    // Start marching at proxy surface
+    var t = length(in.world_pos - ro); 
+    var p = ro + rd * t;
+    
+    // Extract rotation (Normalized columns of model matrix)
+    let mat3 = mat3x3<f32>(
+        obj.model[0].xyz / scale,
+        obj.model[1].xyz / scale,
+        obj.model[2].xyz / scale
+    );
+    
+    var hit = false;
+    // Raymarch Loop
+    for (var i = 0; i < 40; i++) {
+        // Transform p to local unscaled space for SDF eval
+        // q = inv(R) * (p - center) / scale
+        let q = transpose(mat3) * (p - center) / scale;
+        
+        let d_local = get_dist(q, type);
+        let d_world = d_local * scale;
+        
+        if (d_world < 0.001) {
+            hit = true;
+            break;
+        }
+        if (d_world > 3.0 * scale) { 
+            break;
+        }
+        p = p + rd * d_world;
     }
     
-    return vec4<f32>(col, 1.0);
+    if (!hit) {
+        discard;
+    }
+    
+    // Shading
+    // Recompute local pos at hit
+    let q_hit = transpose(mat3) * (p - center) / scale;
+    
+    // Normal calculation:
+    // Calculate normal in local space, then rotate to world.
+    let n_local = get_normal(q_hit, type);
+    let n_world = mat3 * n_local; 
+    
+    let normal = normalize(n_world);
+    let light_dir = normalize(vec3<f32>(1.0, 1.0, 1.0));
+    
+    let diff = max(dot(normal, light_dir), 0.0);
+    let amb = 0.1;
+    
+    let lighting = diff + amb;
+    
+    return vec4<f32>(in.color.rgb * lighting, 1.0);
 }
 )";
 
@@ -328,7 +432,14 @@ void Renderer3D::update_uniforms(const Scene& scene, const Camera& camera, float
     ObjectData data;
     data.model = obj.get_model_matrix();
     data.color = obj.color;
-    // data.params = ...
+    // Map ObjectType enum to float ID
+    float type_id = 0.0f;
+    if (obj.type == ObjectType::SPHERE) type_id = 1.0f;
+    else if (obj.type == ObjectType::CUBE) type_id = 0.0f; 
+    else if (obj.type == ObjectType::TORUS) type_id = 3.0f;
+    else if (obj.type == ObjectType::BOX) type_id = 2.0f;
+    
+    data.params = vec4(type_id, 0, 0, 0);
     obj_data.push_back(data);
     if (obj_data.size() >= kMaxObjects) break;
   }
diff --git a/src/tests/test_3d_render.cc b/src/tests/test_3d_render.cc
index 41bffe6..4be7153 100644
--- a/src/tests/test_3d_render.cc
+++ b/src/tests/test_3d_render.cc
@@ -140,19 +140,27 @@ void init_wgpu() {
 
 void setup_scene() {
   g_scene.clear();
-  // Center Red Cube
-  Object3D center;
+  // Center Red Cube (Wireframe Proxy)
+  Object3D center(ObjectType::CUBE);
   center.position = vec3(0, 0, 0);
   center.color = vec4(1, 0, 0, 1);
   g_scene.add_object(center);
 
-  // Orbiting Green Cubes
+  // Orbiting Objects
   for (int i = 0; i < 8; ++i) {
-    Object3D obj;
+    ObjectType type = ObjectType::SPHERE;
+    if (i % 3 == 1) type = ObjectType::TORUS;
+    if (i % 3 == 2) type = ObjectType::BOX;
+    
+    Object3D obj(type);
     float angle = (i / 8.0f) * 6.28318f;
     obj.position = vec3(std::cos(angle) * 4.0f, 0, std::sin(angle) * 4.0f);
     obj.scale = vec3(0.5f, 0.5f, 0.5f);
-    obj.color = vec4(0, 1, 0, 1);
+    
+    if (type == ObjectType::SPHERE) obj.color = vec4(0, 1, 0, 1);
+    else if (type == ObjectType::TORUS) obj.color = vec4(0, 0.5, 1, 1);
+    else obj.color = vec4(1, 1, 0, 1);
+    
     g_scene.add_object(obj);
   }
 }