refactor(gpu): Implement compile-time BVH toggle via shader composition

Completed Task #18-B optimization and refactoring.
- Replaced runtime branching in shader with compile-time snippet substitution in ShaderComposer.
- Added 'scene_query_bvh.wgsl' and 'scene_query_linear.wgsl' as distinct snippets.
- Refactored Renderer3D to manage two separate pipelines (with and without BVH).
- Updated ShaderComposer to support snippet substitution during composition.
- Verified both paths with test_3d_render (default and --no-bvh).
- Removed temporary shader hacks and cleaned up renderer_3d.wgsl.

1 files changed, 26 insertions, 0 deletions

diff --git a/assets/final/shaders/render/scene_query_linear.wgsl b/assets/final/shaders/render/scene_query_linear.wgsl
new file mode 100644
index 0000000..7bcd96f
--- /dev/null
+++ b/assets/final/shaders/render/scene_query_linear.wgsl
@@ -0,0 +1,26 @@
+#include "math/sdf_shapes"
+
+fn get_dist(p: vec3<f32>, obj_type: f32) -> f32 {
+    if (obj_type == 1.0) { return length(p) - 1.0; } // Unit Sphere
+    if (obj_type == 2.0) { return sdBox(p, vec3<f32>(1.0)); } // Unit Box
+    if (obj_type == 3.0) { return sdTorus(p, vec2<f32>(1.0, 0.4)); } // Unit Torus
+    if (obj_type == 4.0) { return sdPlane(p, vec3<f32>(0.0, 1.0, 0.0), 0.0); }
+    return 100.0;
+}
+
+fn map_scene(p: vec3<f32>, skip_idx: u32) -> f32 {
+    var d = 1000.0;
+    let count = u32(globals.params.x);
+    
+    for (var i = 0u; i < count; i = i + 1u) {
+        if (i == skip_idx) { continue; }
+        let obj = object_data.objects[i];
+        let obj_type = obj.params.x;
+        if (obj_type <= 0.0) { continue; } 
+
+        let q = (obj.inv_model * vec4<f32>(p, 1.0)).xyz;
+        let s = min(length(obj.model[0].xyz), min(length(obj.model[1].xyz), length(obj.model[2].xyz)));
+        d = min(d, get_dist(q, obj_type) * s);
+    }
+    return d;
+}