Refactor UpdateFaceNormalsModifier for improved performance and

robustness

- Added validation to ensure the mesh is not null, improving error
handling.
- Introduced a `setMesh` method to cleanly manage the current mesh
instance.
- Replaced sequential processing with parallelStream for better
performance on large meshes.
- Optimized normal updates by directly modifying existing vectors to
reduce object creation and memory overhead.
- Enhanced code readability and maintainability with a structured
approach.

This update ensures the modifier is faster and more robust, making it
suitable for large-scale mesh operations.

Author: ArtifactForms

src/main/java/mesh/modifier/UpdateFaceNormalsModifier.java

@@ -1,18 +1,77 @@
 package mesh.modifier;
 
+import math.Vector3f;
 import mesh.Face3D;
 import mesh.Mesh3D;
 
+/**
+ * The `UpdateFaceNormalsModifier` recalculates and updates the normals of all
+ * faces in a 3D mesh. This ensures that face normals are consistent with the
+ * current vertex positions and geometry.
+ * 
+ * <p>
+ * This modifier is useful when the geometry of the mesh has been modified, and
+ * accurate face normals are needed for rendering, physics calculations, or
+ * other operations.
+ * </p>
+ */
 public class UpdateFaceNormalsModifier implements IMeshModifier {
 
-    @Override
-    public Mesh3D modify(Mesh3D mesh) {
+	/** The mesh being modified. */
+	private Mesh3D mesh;
 
-        for (Face3D face : mesh.faces) {
-            face.normal = mesh.calculateFaceNormal(face);
-        }
+	/**
+	 * Recalculates and updates the normals of all faces in the given 3D mesh.
+	 * 
+	 * @param mesh The 3D mesh to be modified.
+	 * @return The modified 3D mesh with updated face normals.
+	 * @throws IllegalArgumentException If the provided mesh is null.
+	 */
+	@Override
+	public Mesh3D modify(Mesh3D mesh) {
+		validateMesh(mesh);
+		setMesh(mesh);
+		updateFaceNormals();
+		return mesh;
+	}
 
-        return mesh;
-    }
+	/**
+	 * Iterates over all faces in the mesh and updates their normals in parallel.
+	 * Parallel processing is used to enhance performance for large meshes.
+	 */
+	private void updateFaceNormals() {
+		mesh.faces.parallelStream().forEach(this::updateFaceNormal);
+	}
+
+	/**
+	 * Calculates and updates the normal for a single face.
+	 * 
+	 * @param face The face whose normal is to be updated.
+	 */
+	private void updateFaceNormal(Face3D face) {
+		Vector3f normal = mesh.calculateFaceNormal(face);
+		face.normal.set(normal);
+	}
+
+	/**
+	 * Validates that the provided mesh is not null.
+	 * 
+	 * @param mesh The mesh to validate.
+	 * @throws IllegalArgumentException If the mesh is null.
+	 */
+	private void validateMesh(Mesh3D mesh) {
+		if (mesh == null) {
+			throw new IllegalArgumentException("Mesh cannot be null.");
+		}
+	}
+
+	/**
+	 * Sets the current mesh for processing.
+	 * 
+	 * @param mesh The 3D mesh to set.
+	 */
+	private void setMesh(Mesh3D mesh) {
+		this.mesh = mesh;
+	}
 
 }