diff --git a/fps.txt b/fps.txt
deleted file mode 100644
index 8314797..0000000
--- a/fps.txt
+++ /dev/null
@@ -1,2661 +0,0 @@
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-201
-273
-337
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-467
-343
-435
-403
-327
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-299
-377
-293
-280
-339
-471
-402
-434
-450
-234
-512
-414
-451
-275
-384
-299
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-376
-439
-383
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-504
-446
-295
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-390
-306
-315
-469
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-397
-318
-570
-322
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-375
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-435
-389
-363
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-229
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-284
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-324
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-444
-271
-417
-327
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-412
-315
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-325
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-436
-431
-428
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-331
-431
-256
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-358
-469
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-427
-335
-358
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-282
-328
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-247
-606
-258
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-308
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-323
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-310
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-484
-293
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-483
-304
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-326
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-279
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-362
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-367
-263
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-255
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-267
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diff --git a/includes/RT/BVH.hpp b/includes/RT/BVH.hpp
index 1e2f5e0..d7f77f5 100644
--- a/includes/RT/BVH.hpp
+++ b/includes/RT/BVH.hpp
@@ -25,9 +25,18 @@ struct AABB
 	glm::vec3				max;
 
 	AABB(glm::vec3 min, glm::vec3 max) : min(min), max(max) {}
+	
+	void grow( glm::vec3 p ) { min = glm::min( min, p ), max = glm::max( max, p ); }
+
+    float area() 
+    { 
+        glm::vec3 e = max - min;
+        return (e.x * e.y + e.y * e.z + e.z * e.x); 
+    }
 };
 
-struct BVHStats {
+struct BVHStats
+{
     int min_triangles;
     int max_triangles;
     float average_triangles;
@@ -44,6 +53,8 @@ class BVH
 		void	updateBounds(std::vector <GPUTriangle> &primitives);
 		void	subdivide(std::vector<GPUTriangle> &primitives);
 
+		float	evaluateSah(std::vector<GPUTriangle> &primitives, int axis, float pos);
+
 		int							getSize();
 		int							getLeaves();
 		BVHStats					analyzeBVHLeaves(BVH* root);
diff --git a/scenes/dragon.rt b/scenes/dragon.rt
index afda352..0a7b643 100644
--- a/scenes/dragon.rt
+++ b/scenes/dragon.rt
@@ -24,7 +24,7 @@ pl	0 -2 0		0 1 0		2 // floor
 
 qu	-1 1.999 -1	2 0 0		0 0 2		6
 
-OBJ obj/Dragon_80K.obj
+OBJ obj/Dragon_800K.obj
 
 # po  -1.99 -0.5 -0.5           0 1 0   	0 0 1		1	4
 # po  -0.5 -0.5 -1.99            	  0 1 0   	1 0 0		0	4
diff --git a/shaders/compute.glsl b/shaders/compute.glsl
index 983565a..894dbfd 100644
--- a/shaders/compute.glsl
+++ b/shaders/compute.glsl
@@ -85,20 +85,22 @@ layout(std430, binding = 2) buffer TriangleBuffer
 	GPUTriangle triangles[];
 };
 
-layout(std430, binding = 3) buffer MaterialBuffer
+layout(std430, binding = 3) buffer BvhBuffer
+{
+	GPUBvh bvh[];
+};
+
+layout(std430, binding = 4) buffer MaterialBuffer
 {
 	GPUMaterial materials[];
 };
 
-layout(std430, binding = 4) buffer LightsBuffer
+layout(std430, binding = 5) buffer LightsBuffer
 {
     int lightsIndex[];
 };
 
-layout(std430, binding = 5) buffer BvhBuffer
-{
-	GPUBvh bvh[];
-};
+
 
 
 layout(std140, binding = 0) uniform CameraData
diff --git a/srcs/RT.cpp b/srcs/RT.cpp
index 1dfb72b..47301b1 100644
--- a/srcs/RT.cpp
+++ b/srcs/RT.cpp
@@ -20,52 +20,53 @@ int main(int argc, char **argv)
 		return (1);
 
 	Window		window(&scene, WIDTH, HEIGHT, "RT_GPU", 0);
-	// Shader		shader("shaders/vertex.vert", "shaders/frag.frag", "shaders/compute.glsl");
-	Shader		shader("shaders/vertex.vert", "shaders/frag.frag", "shaders/debug.glsl");
+	Shader		shader("shaders/vertex.vert", "shaders/frag.frag", "shaders/compute.glsl");
+	// Shader		shader("shaders/vertex.vert", "shaders/frag.frag", "shaders/debug.glsl");
 
 	GLint max_gpu_size;
 	glGetIntegerv(GL_MAX_SHADER_STORAGE_BLOCK_SIZE, &max_gpu_size);
 
 	const std::vector<GPUObject> &object_data = scene.getObjectData();
 	const std::vector<GPUTriangle> &triangle_data = scene.getTriangleData();
-
+	const std::vector<GPUBvh> &bvh_data = scene.getBVH();
 	const std::vector<GPUMaterial> &material_data = scene.getMaterialData();
 
 	std::cout << "Sending " << object_data.size() << " objects for " << \
 				object_data.size() * sizeof(GPUObject) + \
 				triangle_data.size() * sizeof(GPUTriangle) + \
+				bvh_data.size() * sizeof(GPUBvh) + \
 				material_data.size() * sizeof(GPUMaterial) \
 				<< " / " << max_gpu_size << " bytes" << std::endl;
 
 	GLuint objectSSBO;
     glGenBuffers(1, &objectSSBO);
 	glBindBuffer(GL_SHADER_STORAGE_BUFFER, objectSSBO);
-	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GPUObject) * object_data.size(), nullptr, GL_STATIC_DRAW);
+	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GPUObject) * object_data.size(), object_data.data(), GL_STATIC_DRAW);
 	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, objectSSBO);
 
 	GLuint trianglesSSBO;
     glGenBuffers(1, &trianglesSSBO);
 	glBindBuffer(GL_SHADER_STORAGE_BUFFER, trianglesSSBO);
-	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GPUTriangle) * triangle_data.size(), nullptr, GL_STATIC_DRAW);
+	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GPUTriangle) * triangle_data.size(), triangle_data.data(), GL_STATIC_DRAW);
 	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2, trianglesSSBO);
 
+	GLuint bvhSSBO;
+	glGenBuffers(1, &bvhSSBO);
+	glBindBuffer(GL_SHADER_STORAGE_BUFFER, bvhSSBO);
+	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GPUBvh) * bvh_data.size(), bvh_data.data(), GL_STATIC_DRAW);
+	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 3, bvhSSBO);
+
 	GLuint materialSSBO;
     glGenBuffers(1, &materialSSBO);
 	glBindBuffer(GL_SHADER_STORAGE_BUFFER, materialSSBO);
 	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(GPUMaterial) * material_data.size(), nullptr, GL_STATIC_DRAW);
-	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 3, materialSSBO);
+	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 4, materialSSBO);
 	
 	GLuint lightSSBO;
 	glGenBuffers(1, &lightSSBO);
 	glBindBuffer(GL_SHADER_STORAGE_BUFFER, lightSSBO);
 	glBufferData(GL_SHADER_STORAGE_BUFFER, scene.getGPULights().size() * sizeof(int), nullptr, GL_STATIC_DRAW);
-	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 4, lightSSBO);
-
-	GLuint bvhSSBO;
-	glGenBuffers(1, &bvhSSBO);
-	glBindBuffer(GL_SHADER_STORAGE_BUFFER, bvhSSBO);
-	glBufferData(GL_SHADER_STORAGE_BUFFER, scene.getBVH().size() * sizeof(GPUBvh), nullptr, GL_STATIC_DRAW);
-	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 5, bvhSSBO);
+	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 5, lightSSBO);
 
 
 	GLuint cameraUBO;
@@ -99,13 +100,7 @@ int main(int argc, char **argv)
 	{
 
 		glUseProgram(shader.getProgramCompute());
-
-		glBindBuffer(GL_SHADER_STORAGE_BUFFER, objectSSBO);
-		glBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, object_data.size() * sizeof(GPUObject), object_data.data());
-
-		glBindBuffer(GL_SHADER_STORAGE_BUFFER, trianglesSSBO);
-		glBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, triangle_data.size() * sizeof(GPUTriangle), triangle_data.data());
-
+		
 		glBindBuffer(GL_SHADER_STORAGE_BUFFER, materialSSBO);
 		glBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, material_data.size() * sizeof(GPUMaterial), material_data.data());
 
@@ -113,16 +108,11 @@ int main(int argc, char **argv)
 		std::vector<int> gpu_lights_array(gpu_lights.begin(), gpu_lights.end());
 		glBindBuffer(GL_SHADER_STORAGE_BUFFER, lightSSBO);
 		glBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, gpu_lights_array.size() * sizeof(int), gpu_lights_array.data());
-		
-		std::vector<GPUBvh> gpu_bvh = scene.getBVH();
-		glBindBuffer(GL_SHADER_STORAGE_BUFFER, bvhSSBO);
-		glBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, gpu_bvh.size() * sizeof(GPUBvh), gpu_bvh.data());
-		
 
 		Camera *camera = scene.getCamera();
 
 		// performance profiling
-		if (true)
+		if (false)
 		{
 			float time = (float)(glfwGetTime()) ;
 
@@ -161,7 +151,7 @@ int main(int argc, char **argv)
 
 		shader.set_int("u_frameCount", window.getFrameCount());
 		shader.set_int("u_objectsNum", object_data.size());
-		shader.set_int("u_bvhNum", gpu_bvh.size());
+		shader.set_int("u_bvhNum", scene.getBVH().size());
 		shader.set_int("u_lightsNum", gpu_lights.size());
 		shader.set_int("u_pixelisation", window.getPixelisation());
 		shader.set_float("u_time", (float)(glfwGetTime()));
diff --git a/srcs/class/BVH.cpp b/srcs/class/BVH.cpp
index 4650fe1..c7d0459 100644
--- a/srcs/class/BVH.cpp
+++ b/srcs/class/BVH.cpp
@@ -44,26 +44,85 @@ void	BVH::updateBounds(std::vector<GPUTriangle> &primitives)
 	}
 }
 
+
+float	BVH::evaluateSah(std::vector<GPUTriangle> &primitives, int axis, float pos)
+{
+    AABB left_box(glm::vec3(1e30f), glm::vec3(-1e30f));
+	AABB right_box(glm::vec3(1e30f), glm::vec3(-1e30f));
+
+    int left_count = 0;
+	int right_count = 0;
+
+    for (unsigned int i = 0; i < _primitive_count; i++)
+    {
+        GPUTriangle triangle = primitives[_first_primitive + i];
+		glm::vec3 centroid = (triangle.position + triangle.vertex1 + triangle.vertex2) / 3.0f;
+
+        if (centroid[axis] < pos)
+        {
+            left_count++;
+            left_box.grow( triangle.position );
+            left_box.grow( triangle.vertex1 );
+            left_box.grow( triangle.vertex2 );
+        }
+        else
+        {
+            right_count++;
+            right_box.grow( triangle.position );
+            right_box.grow( triangle.vertex1 );
+            right_box.grow( triangle.vertex2 );
+        }
+    }
+    float cost = left_count * left_box.area() + right_count * right_box.area();
+    return (cost > 0 ? cost : 1e30f);
+}
+
+
+
 void	BVH::subdivide(std::vector<GPUTriangle> &primitives)
 {
-	if (_primitive_count <= 100)
+	if (_primitive_count <= 4)
 		return ;
 
 	glm::vec3 extent = _aabb.max - _aabb.min;
 	
-	int axis = 0; 
-	if (extent.y > extent.x) axis = 1;
-	if (extent.z > extent[axis]) axis = 2;
+	const int num_test_per_axis = 5;
 
-	float split_pos = _aabb.min[axis] + extent[axis] * 0.5f;
+	int best_axis = 0;
+	float best_pos = 0;
+	float best_cost = 1e30f;
+
+	for (int axis = 0; axis < 3; axis++)
+	{
+		float start_pos = _aabb.min[axis];
+		float end_pos = _aabb.max[axis];
+
+		for (int i = 0; i < num_test_per_axis; i++)
+		{
+			float split_t = (i + 1) / (num_test_per_axis + 1.0f);
+			float candidate_pos = start_pos + (end_pos - start_pos) * split_t;
+
+			float cost = evaluateSah(primitives, axis, candidate_pos);
+
+			if (cost < best_cost)
+			{
+				best_pos = candidate_pos;
+				best_axis = axis;
+				best_cost = cost;
+			}
+		}
+	}
+
+	int axis = best_axis;
+	float split_pos = best_pos;
 
 	int i = _first_primitive;
 	int j = _first_primitive + _primitive_count - 1;
 
 	while (i <= j)
 	{
-		glm::vec3 centroid = primitives[i].position + primitives[i].vertex1 + primitives[i].vertex2;
-		centroid /= 3.0f;
+		GPUTriangle triangle = primitives[i];
+		glm::vec3 centroid = (triangle.position + triangle.vertex1 + triangle.vertex2) / 3.0f;
 
 		if (centroid[axis] < split_pos)
 			i++;